Displays

In order to assess the global evolution of aerosol parameters affecting climate change, a long-term trend analyses of aerosol optical properties were performed on time series from 52 stations situated across five continents. The time series of measured scattering, backscattering and absorption coefficients as well as the derived single scattering albedo, backscattering fraction, scattering and absorption Ångström exponents covered at least 10 years and up to 40 years for some stations. The non-parametric seasonal Mann-Kendall (MK) statistical test associated with several prewhitening methods and with the Sen’s slope were used as main trend analysis methods. Comparisons with General Least Mean Square associated with Autoregressive Bootstrap (GLS/ARB) and with standard Least Mean Square analysis (LMS) enabled confirmation of the detected MK statistically significant trends and the assessment of advantages and limitations of each method. Currently, scattering and backscattering coefficients trends are mostly decreasing in Europe and North America and are not statistically significant in Asia, while polar stations exhibit a mix of increasing and decreasing trends. A few increasing trends are also found at some stations in North America and Australia. Absorption coefficients time series also exhibit primarily decreasing trends. For single scattering albedo, 52% of the sites exhibit statistically significant positive trends, mostly in Asia, Eastern/Northern Europe and Arctic, 18% of sites exhibit statistically significant negative trends, mostly in central Europe and central North America, while the remaining 30% of sites have trends, which are not statistically significant. In addition to evaluating trends for the overall time series, the evolution of the trends in sequential 10 year segments was also analyzed. For scattering and backscattering, statistically significant increasing 10 year trends are primarily found for earlier periods (10 year trends ending in 2010-2015) for polar stations and Mauna Loa. For most of the stations, the present-day statistically significant decreasing 10 year trends of the single scattering albedo were preceded by not statistically significant and statistically significant increasing 10 year trends. The effect of air pollution abatement policies in continental North America is very obvious in the 10 year trends of the scattering coefficient – there is a shift to statistically significant negative trends in 2010-2011 for all stations in the eastern and central US. This long-term trend analysis of aerosol radiative properties with a broad spatial coverage enables a better global view of potential aerosol effects on climate changes.

How to cite: Collaud Coen, M., Andrews, E., Lund Myhre, C., Hand, J., Pandolfi, M., and Laj, P. and the SARGAN: trend analysis of aerosol radiative properties: Multidecadal trend analysis of aerosol radiative properties at a global scale , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3115, https://doi.org/10.5194/egusphere-egu2020-3115, 2020.

Atmospheric aerosols are known to play a key role in Earth’s radiative budget, although the quantification of their climate forcing is still highly uncertain. In order to improve the scientific understanding of their climatic effect, in-situ ground-based aerosol properties observations are needed by the research community. Such data would also allow the global assessment of the effect of environmental policies over both the short and the long term.

To develop a robust and consistent view over time of the worldwide variability of aerosol properties, data resulting from a fully-characterized value chain, including uncertainty estimation, is needed.

The present work is part of a wider project, having among its goals the investigation of the variability of climate-relevant aerosol properties observed at all sites connected to the Global Atmospheric Watch network, whose data are publicly available from the World Data Centre for Aerosols and follow the aforementioned specifications.

This work focuses on aerosol optical proprieties, i.e. the aerosol light scattering coefficient (σ_sp), the aerosol light absorption coefficient (σ_ap), single scattering albedo (ω_o) and both scattering and absorption Ångström exponents (å_sp and å_ap).

The analysis includes 108 yearly datasets collected either during 2016 or 2017 at different sites: 53 for absorption and 55 for scattering coefficient datasets, respectively. For 29 of these sites it was also possible to compute single scattering albedo.

The spatial variability in extensive and intensive optical properties was analysed in terms of each site’s geographical location (either polar, continental, coastal or mountain) and its footprint (from pristine to urban, representing increasing levels of anthropogenic influence).

The results highlight the impact of anthropogenic emissions and biomass burning on absolute levels and annual variability. The effect of sea spray or long range transport of dust is also evident for several sites, along with the influence of regional emissions. The largest seasonality in aerosol loading was observed at mountain sites under mixed footprint conditions, while the lowest seasonality occurred at urban sites. Urban sites also exhibited the highest σsp and σap values. The lowest levels in σ_sp and σ_ap were observed at some polar sites, along with few coastal and mountain sites, despite their typically mixed footprint.

Acknowledgements

The authors acknowledge WMO-GAW World Data Centre on Aerosol for providing data available at http://ebas.nilu.no

How to cite: Bigi, A., Collaud Coen, M., Andrews, E. J., Rose, C., Lund Myhre, C., Fiebig, M., Schulz, M., Ogren, J. A., Gliss, J., Mortier, A., Wiedensohler, A., Pandolfi, M., Petäja, T., Kim, S.-W., Aas, W., Putaud, J.-P., Mayol-Bracero, O., Keywood, M., Labrador, L., and Laj, P.: Global variability of aerosol optical properties retrieved from the network of GAW near-surface observatories, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3568, https://doi.org/10.5194/egusphere-egu2020-3568, 2020.

Multiwavelength aerosol optical depth (AOD) has been defined as an essential climate variable for the Global Climate Observing System (GCOS) and the Global Atmosphere Watch (GAW) Program of the World Meteorological Organization. It is the most important parameter related to aerosol radiative forcing studies. PMOD/WRC have developed the Precision Filter Radiometer (PFR) that has been used for long term AOD measurements under a GAW-PFR Network of sun-photometers started in 1995 at Davos Switzerland and from 1999 at other locations, worldwide.

Here we present:

An overview of the results of the long term GAW-PFR AOD series for four high altitude stations (Izana/Spain, Mauna Loa/USA, Mt. Walliguan/China and Jungfraujoch/Switzerland). Mean AODs at 500nm were from 0.015 up to 0.096 with small negative changes per year for all stations.

An overview of the results for polar stations (Ny Ålesund/Norway, Summit/Denmark, Marambio/Finland). Ny Ålesund mean AODs at 500nm were almost double compared with the other stations.

How to cite: Kazadzis, S., Kouremeti, N., and Groebner, J.: Aerosol Optical Depth Measurements at high altitude and polar WMO Global Atmospheric Watch - PFR Network Stations , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6161, https://doi.org/10.5194/egusphere-egu2020-6161, 2020.

Aerosol particles are essential constituents of the Earth’s atmosphere, impacting the earth radiation balance directly by scattering and absorbing solar radiation, and indirectly by acting as cloud condensation nuclei. In contrast to most greenhouse gases, aerosol particles have short atmospheric residence time resulting in a highly heterogeneous distribution in space and time. There is a clear need to document this variability at regional scale through observations involving, in particular, the in-situ near-surface segment of the atmospheric observations system. This paper will provide the widest effort so far to document variability of climate-relevant in-situ aerosol properties (namely wavelength dependent particle light scattering and absorption coefficients, particle number concentration and particle number size distribution) from all sites connected to the Global Atmosphere Watch network. High quality data from more than 90 stations worldwide have been collected and controlled for quality and are reported for a reference year in 2017, providing a very extended and robust view of the variability of these variables worldwide. The range of variability observed worldwide for light scattering and absorption coefficients, single scattering albedo and particle number concentration are presented together with preliminary information on their long-term trends and comparison with model simulation for the different stations. The scope of the present paper is also to provide the necessary suite of information including data provision procedures, quality control and analysis, data policy and usage of the ground-based aerosol measurements network. It delivers to users of the World Data Centre on Aerosol, the required confidence in data products in the form of a fully-characterized value chain, including uncertainty estimation and requirements for contributing to the global climate monitoring system.

How to cite: Laj, P., Rose, C., Bigi, A., Collaud Coen, M., Andrews, E., Lund Myhre, C., Fiebig, M., Aas, W., Wiedensohler, A., Schulz, M., Mortier, A., Gliss, J., Putaud, J.-P., Kim, S.-W., Mayol, O., Keywood, M., Petäjä, T., Pandolfi, M., Labrador, L., and Ogren, J. and the SARGAN team: A global analysis of climate-relevant aerosol properties retrieved from the network of GAW near-surface observatories, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2147, https://doi.org/10.5194/egusphere-egu2020-2147, 2020.

This study presents a multi-parameter analysis of aerosol trends over the last two decades at regional and global scales. Regional time series have been computed for a set of nine optical, chemical composition and mass aerosol properties by using the observations of several ground-based networks. From these regional time series the aerosol trends have been derived for different regions of the world. Most of the properties related to aerosol loading exhibit negative trends, both at the surface and in the total atmospheric column. Significant decreases of aerosol optical depth (AOD) are found in Europe, North America, South America and North Africa, ranging from −1.3 %/yr to −3.1 %/yr. An error and representativity analysis of the incomplete observational data has been performed using model data subsets in order to investigate how likely the observed trends represent the actual trends happening in the regions over the full study period from 2000 to 2014. This analysis reveals that significant uncertainty is associated with some of the regional trends due to time and space sampling deficiencies. The set of observed regional trends has then been used for the evaluation of the climate models and their skills in reproducing the aerosol trends. Model performance is found to vary depending on the parameters and the regions of the world. The models tend to capture trends in AOD, column Angstrom exponent, sulfate and particulate matter well (except in North Africa), but show larger discrepancies for coarse mode AOD. The rather good agreement of the trends, across different aerosol parameters between models and observations, when co-locating them in time and space, implies that global model trends, including those in poorly monitored regions, are likely correct. The models can help to provide a global picture of the aerosol trends by filling the gaps in regions not covered by observations. The calculation of aerosol trends at a global scale reveals a different picture from the one depicted by solely relying on ground based observations. Using a model with complete diagnostics (NorESM2) we find a global increase of AOD of about 0.2 %/yr between 2000 and 2014, primarily caused by an increase of the loads of organic aerosol, sulfate and black carbon.

How to cite: Mortier, A., Gliss, J., and Schulz, M. and the climate models and aerosol measurements group: Evaluation of climate model aerosol trends with ground-based observations over the last two decades – an AeroCom and CMIP6 analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17221, https://doi.org/10.5194/egusphere-egu2020-17221, 2020.

Within the framework of the AeroCom (Aerosol Comparisons between Observations and Models) initiative, the present day modelling of aerosol optical properties has been assessed using simulated data representative for the year 2010, from 14 global aerosol models participating in the Phase III Control experiment. The model versions are close or equal to those used for CMIP6 and AerChemMIP and inform also on bias in state of the art Earth-System-Models (ESMs).
Modelled column optical depths (total, fine and coarse mode AOD) and Angstrom Exponents (AE) were compared both with ground based observations from the Aerosol Robotic Network (AERONET, version 3) and space based observations from the AATSR instrument. In addition, the modelled AODs were compared with MODIS (Aqua and Terra) data and a satellite AOD data-set (MERGED-FMI) merged from 12 different individual AOD products. Furthermore, for the first time, the modelled near surface scattering (under dry conditions) and absorption coefficients were evaluated against measurements made at low relative humidity at surface in-situ GAW sites. 
The AeroCom MEDIAN and most of the participating models underestimate the optical properties investigated, relative to remote sensing observations. AERONET AOD is underestimated by 21%+/-17%. Against satellite data, the model AOD biases range from -38% (MODIS-terra) to -17% (MERGED-FMI). Correlation coefficients of model AODs with AERONET, MERGED-FMI and AATSR-SU are high (0.8-0.9) and slightly lower against the two MODIS data-sets (0.6-0.8). Investigation of fine and coarse AODs from the MEDIAN model reveals biases of -10%+/-20% and -41%+/-29% against AERONET and -13% and -24% against AATSR-SU, respectively. The differences in model bias against AERONET and AATSR-SU are in agreement with the established bias of AATSR against AERONET. These results indicate that most of the AOD bias is due to missing coarse AOD in the regions covered by these observations. Underestimates are also found when comparing the models against the surface GAW observations, showing AeroCom MEDIAN mean bias and inter-model variation of -44%+/-22% and -32%+/-34% for scattering and absorption coefficients, respectively. Dry scattering shows higher underestimation than AOD at ambient relative humidity and is in agreement with recent findings that suggest that models tend to overestimate scattering enhancement due to hygroscopic growth. 
Considerable diversity is found among the models in the simulated near surface absorption coefficients, particularly in regions associated with dust (e.g. Sahara, Tibet), biomass burning (e.g. Amazonia, Central Australia) and biogenic emissions (e.g. Amazonia). Regions associated with high anthropogenic BC emissions such as China and India exhibit comparatively good agreement for all models. Evaluation of modelled column AEs shows an underestimation of 9%+/-24% against AERONET and -21% against AATSR-SU. This suggests that models tend to overestimate particle size, with implications for lifetime and radiative transfer calculations. An investigation of modelled emissions, burdens and lifetimes, mass-specific-extinction coefficients (MECs) and optical depths (ODs) for each species and model reveals considerable diversity in most of these parameters. Inter-model spread of aerosol species lifetime appears to be similar to that of mass extinction coefficients, suggesting that AOD uncertainties are still associated to a broad spectrum of parameterised aerosol processes.

How to cite: Gliß, J., Mortier, A., and Schulz, M. and the AeroCom modellers and aerosol measurements team: Multi-model evaluation of aerosol optical properties in the AeroCom phase III Control experiment, using ground and space based observations from AERONET, MODIS, AATSR and a merged satellite product as well as surface in-situ observations from GAW sites, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18390, https://doi.org/10.5194/egusphere-egu2020-18390, 2020.

Based on the importance of the effects of aerosols on climate pattern change, our study contributes towards a better understanding of the Aerosol Optical Depth (AOD) trends from different datasets and the contribution of each dominant aerosol over Iran. A long-term AOD dataset (1980–2018) from the reanalysis-based Modern Era Retrospective Analysis for Research and Applications (MERRA-2) and the satellite-based Moderate Resolution Imaging Spectroradiometer (MODIS) /Terra Collection 6.1(C6.1) and Level 2 (L2) in the years 2001-2018. The result of AOD trend showed some differences between MERRA-2 and MODIS in autumn and winter.  But, generally, the increasing and slightly decreasing trends appeared over the southwest and north of the country, respectively. The upward trend was mainly observed in the southwest of Iran because of the proximity to the major source areas of natural mineral dust in spring and summer of both AOD datasets which was also obtained in the regional trend analysis and the city of Ahvaz experienced a strong positive trend compared with other selected cities. Also, an unforeseen downward trend was observed in the last decade. Finally, the classification of major aerosol types during 1980-2018 indicated that the mixed aerosols (43.28%) and clean marine (37.38%) were the dominate aerosols followed by the clean continental (9.78%) and desert dust (5.56%) with minor contributions of biomass burning/urban industrial (3.98%) aerosols. Later, the increase of desert dust around 2010 was another obvious result in spring and summer. Our study results indicate that the variation in dust aerosols has a key role in determining the AOD changes in Iran which are contributed in regional climate change and environmental evolutions.

How to cite: Yousefi, R., Wang, F., Ge, Q., Shaheen, A., and Luterbacher, J.: Long-term AOD trend analysis and Classification of major aerosol types over Iran from 1980 to 2018, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1831, https://doi.org/10.5194/egusphere-egu2020-1831, 2020.

Abstract: Ecological region in southern China has been perennially affected by monsoon climate and anthropogenic emissions, resulting in complex aerosol components and frequent long-range transport. In this study, a Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model is applied to estimate aerosol radiative forcing (ARF) and multiple aerosol observation datasets is used to estimate the aerosol chemical components and optical properties. The aerosol loading and the radiative effects in the ecological region exhibited strong seasonal changes. The average major components (NH₄⁺, NO₃⁻, SO₄²⁻) in Total water soluble ionic (TWSI) ,organic carbon (OC) concentration, the ratio of organic carbon to element carbon (OC/EC) and biogenic secondary organic aerosol (BSOA) tracers were 3.20±1.22 μg·m^-3, 2.19±1.39 μg·m^-3, 3.17 and 74.00±35.23 ng·m^-3 in the dry season and 2.22±0.91 μg·m^-3, 3.14±1.62 μg·m^-3, 7.13 and 186.34±113.82 ng·m^-3 in the wet season, respectively. The average radiative forcing at the top of atmosphere (TOA) is -11.73±11.36 W/m² and -0.41±10.08 W/m² in dry and wet season. When the aerosol single scattering albedo (SSA) less than 0.9, the retrieve frequency in wet season reached account for 75%. The increase of OC and BSOA transformed by forests in the wet season weaken the cooling effects. However, the dry season is mainly composed of anthropogenic inorganic aerosols, which enhances the scattering effect. The aerosol observation baseline also verified the seasonal variation of ARF in the ecological region. Driven by multiple factors such as meteorological conditions, emission sources, and the mixed state of particulate matter, the transport patterns of air masses in ecological area exhibits completely opposite affects to ARF.

How to cite: Yining, M. and Jinyuan, X.: Spatial and temporal heterogeneity in aerosol radiative effects over ecological area in south China: Composition and transmission implications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4351, https://doi.org/10.5194/egusphere-egu2020-4351, 2020.

Due to their multiple effects on climate and human health, aerosol particles are a key component of the Earth’s atmosphere. The understanding of these effects however remains incomplete, which in turn affects their quantification at the present time as well as future predictions. These limitations highlight the need for continuing the efforts to organize long term monitoring of the climate-relevant aerosol properties in as broad a network as possible.

The value of such measurements, which are performed in compliance with homogenous protocols and meet high quality standards, is clearly demonstrated in the present analysis. This work, which is focused on the particle number concentration and particle number size distribution (PNSD), is part of a wider project, one of the objectives of which is to document the variability of climate-relevant aerosol properties based on available in-situ near-surface measurements. To investigate the spatial variability of the abovementioned aerosol physical properties, observations collected at 57 sites connected to the Global Atmosphere Watch (GAW) network were analysed for a reference year (2017). Measurements performed with condensation particle counters (CPC, 21 sites) and mobility particle size spectrometers (MPSS, 36 sites) were both included in the analysis; in the latter case, the total particle number concentration, N_tot, was calculated over the diameter range 10 – 500 nm.

As a result of enhanced sources, N_tot is generally higher during warmer seasons at all sites (in connection with atmospheric boundary layer dynamics for mountain sites). In addition, based on available MPSS data, the major contribution of Aitken mode particles (30-100 nm) to the total particle number concentration also appears as a common feature of all environments. In contrast, the observed levels of N_tot, between 10¹ and 10⁴ cm^-3, and the magnitude of its seasonal cycle, exhibit, together with the variations of the PNSD, some distinctive behaviour for the different geographical categories and environmental footprint classes, with additional site-dependent characteristics. Among other factors (including the nature and proximity of the particles sources), the level of anthropogenic influence appears to strongly affect the observations.

This work will be completed in the near future with a trend analysis to document the temporal variability of the particle number concentration and PNSD.

How to cite: Rose, C. and the co-workers: Global variability of aerosol physical properties retrieved from the network of GAW near-surface observatories, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9653, https://doi.org/10.5194/egusphere-egu2020-9653, 2020.

Air pollution problem in megacities in China has been significantly improved as annual average PM_2.5 in 2019 in Beijing was 42 µg/m³. But is still a serious problem in many smaller cities. Sanmenxia is located in the Fen-Wei Plain, close to China's largest coal base. The annual average PM_2.5 of Sanmenxia decreased from 72 µg/m³ in 2015 to 59 µg/m³ in 2019. The highly concentrated industries, especially coal industries, heavy traffic, and the typical terrain that it locates nearby the gorge of the Yellow river, make Sanmenxia a highly polluted city. The highest average PM_2.5 was ~100 µg/m³ in winter. Non-refractory PM₁ (NR-PM₁) species including organic aerosol (Org), sulfate (SO₄), nitrate (NO₃), ammonium (NH₄) and chloride (Chl) were measured at Sanmenxia Environmental Protection Bureau (34.794°N,111.171°E) by the ACSM at a time resolution of ~5 min from December 21, 2018 to January 21, 2019. High time resolution of online meteorological variables, as well as precursor gases, OC/EC, and trace elements were also collected at the site, aiming to characterize the pollution sources and evolution mechanisms of aerosol chemical composition. A long haze episode lasted for 16 days was observed with NR-PM₁ = 76±33 µg/m³, PM_2.5 = 180±89 µg/m³. During this episode, the primary species, nitrate accounted for 32% of NR-PM₁ due to high emission of NOx. Positive matrix factorization (PMF) analysis indicates that industrial emission, coal combustion, traffic emission, and secondary species (sulfate + nitrate + ammonium + secondary organic aerosol) were the major sources of pollution. The diurnal variations of pollutants in Sanmenxia were affected significantly by the vertical movement of air flows, but were not sensitive to the regional transport.

How to cite: Wang, Q., Sun, Y., Li, J., Chen, Y., and Li, Y.: Characterization of aerosol composition and sources in a polluted city in Central China , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3248, https://doi.org/10.5194/egusphere-egu2020-3248, 2020.

Light-absorbing carbonaceous aerosols such as black and brown carbon (BC and BrC) and humic-like substances (HULIS) have pronounced effects on the earth’s radiative balance and tropospheric photochemistry. In India, large heterogeneities exist for BC and organic carbon (OC) emission inventories, which necessitates regionally-representative ground-based measurements. Such measurements are spatially scattered for BC, rare for BrC and non-existent for HULIS. This severely limits a robust understanding of the optical and chemical properties of these aerosols, and consequently, their climate effects. To address this issue, the present study reports optical and chemical properties of wintertime (December 2018-February 2019) BC, BrC and HULIS at a rural receptor site in the highly polluted eastern Indo-Gangetic Plain (IGP), India. A 7 wavelength aethalometer was deployed to measure time-resolved BC mass concentration, and absorption coefficients (b_abs) and Angstrom exponent (AE) of BrC. Separation of aqueous and organic BrC (BrC_aq and BrC_org) and HULIS fractions via a multi-step chemical extraction procedure followed by optical measurements (UV-Vis, fluorescence and FT-IR), and supplementary measurements of OC, water-soluble organic carbon (WSOC) and ionic species led to better insights into the potential chromophore composition and their relative importance in constraining aerosol optical properties.

The daily averaged BC mass concentration was 15.4±9.5 μg m^-3 during winter, where the biomass burning (BB) contribution was 25±5%. The diurnal profile of BC_BB and BrC light absorption coefficient (b_{abs_BrC}) showed a prominent morning peak (0700-0800 H) characterized by mixed fossil fuel and biofuel emission and a gradual increase towards night due to enhanced primary BB emission from cooking activities and lowering of the mixing depth. The regionally transported BB plume from northwestern IGP contributed substantial BC and BrC to this receptor location in the eastern end of the corridor, which was supported by concentration-weighted air mass trajectories (CWTs).

The BrC_org light absorption at 365 nm (b_{abs_BrC_org}) was almost 2 times compared to that of BrC_aq (b_{abs_BrC_aq}) (36±7.1 vs 18.3±4.3 Mm^-1), which suggested a dominance of non-polar polyconjugated BrC chromophores. This was also supported by the increasing trend of water-insoluble BrC from 49±10% at 365 nm to 64±21% at 550 nm, with averaged contributions of 49±8% at 300-400 nm and 67±9% at 400-550 nm, respectively. A strong correlation between WSOC and NO₃^- (r=0.78, p<0.01) and WSOC and NH₄⁺ (r=0.63, p<0.01) indicated the possibility of nighttime secondary organic aerosol formation. A prominent fluorescence peak at ~409 nm for BrC_aq confirmed the presence of HULIS, and b_{abs_BrC_aq} was dominated by the low-polarity HULIS-n fraction. AE of individual HULIS fractions increased by 7-36% towards the more polar HULIS-a and highly-polar water-soluble organic matter (HPWSOM) compared to the less polar HULIS-n for the 300-700 nm range. Distinct FTIR peaks at 3400 cm^-1, 1710 cm^-1 and 1643 cm^-1 suggested abundance of C-H, C=O and C=C functional groups, respectively, in the BrC chromophores. Overall, it appeared that the regionally transported BB plume significantly enriches BrC and HULIS in the eastern part of the IGP corridor.   

How to cite: Dey, S., Rana, A., Rawat, P., and Sarkar, S.: Optical and chemical properties of wintertime light-absorbing aerosols in the eastern Indo-Gangetic Plain, India, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-655, https://doi.org/10.5194/egusphere-egu2020-655, 2020.

To better understand the abundance and sources of water-soluble inorganic ions (WSIIs), semi-continuous measurements of WSIIs were performed during autumn 2015 and spring 2016 at a high-altitude background station (2,862 m above sea level) on the summit of Mt. Lulin in central Taiwan. During autumn, the mass concentration of PM_2.5, major WSIIs, and CO increased significantly from 12:00 to 18:00 hrs local standard time (LST), whereas the visibility and concentration of O₃ decreased at the same time. The backward trajectories analyses showed that the sampling site was under the influence of lifted air masses by the upslope wind from 12:00 to 18:00 hrs. Thus the mountain-valley (M-V) circulation could be the major driving force for the observed aerosol diurnal patterns over the study region during autumn. In sharp contrast to autumn, five high aerosol loading events were observed during spring with each event lasting for a few days. These events were synchronized with the long-range transport of biomass burning (BB) smoke emissions from the Indochina region, as revealed from the fire count map and backward trajectories. The plumes appear to mask their characteristic diurnal features that are driven by the local M-V circulation. These plumes also affected the acidity of ambient aerosol. During BB events, aerosol was found to be relatively more alkaline in nature as revealed by higher molar ratio of [NH₄⁺]_calc/[NH₄⁺]_meas during BB events (0.88 ± 0.25) than that of the whole spring season (0.81 ± 0.33). The third BB event (BB3), March 29 to April 04, 2016, was the most prominent one among all BB events. During BB3, the mass concentration of PM_2.5, NH₄⁺, K⁺, NO₃^- and SO₄^2- increased from 8.3 to 29, 0.01 to 2.0, 0.02 to 0.4, 0.01 to 1.6, and 0.4 to 4.1 μg m^-3, respectively as compared to before the event. A fog event (March 31; 0:00 to 10:00 LST) was also observed during the BB3 event that decreased the mass concentration of all the species significantly. It suggested that aerosol scavenging and cloud-active processing may occur in this fog event.

How to cite: Singh, A., Chen, W.-R., and Lee, C.-T.: Semi-continuous measurements of water-soluble inorganic ions over a high-altitude background site in central Taiwan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12251, https://doi.org/10.5194/egusphere-egu2020-12251, 2020.

Atmospheric traffic-related elements (TRE) generated from traffic-related emissions have been linked to a wide range of human diseases and also affect the ecosystem. This study focuses on data from the Nigerian air quality network along the segment of the National Highway Roads (NHR), inner-city Major Roads (MR) and Rural Roads (RR) in Ibadan. The aim of this near-road monitoring was to assess the levels of TRE, determine the particulate matter (PM₁₀) concentrations and mineralogical composition of the PM₁₀ particles.

Sixty particulate matter (PM₁₀) samples were collected from 5 traffic-related stations (2-NHR; 2-MR; 1-RR) (six samples from each station) in the study area using traffic-related high-volume air sampler with PM₁₀ cut-off on cellulose filter. PM₁₀ concentration was calculated from the difference in weight of the filter and flow rate of the sampler while the mineralogical composition of the PM₁₀ was determined by single-particle analysis using scanning electron microscopy and energy-dispersive x-ray spectroscopy (SEM/EDXS) techniques, and the TRE were determined by inductively coupled plasma-optical emission spectrometry (ICP-OES).

The results of the PM₁₀ concentration showed that NHR had the highest concentration of 1194.30 µg/m³, while the lowest concentration was observed in RR (36.33 µg/m³), these correspond to the level of traffic density in both stations, the former having 60,000 vehicle/day while the later had <2000 vehicle/day. More than 80% of the PM₁₀ concentrations in the NHR and the MR were classified as being unhealthy-hazardous to humans living very close to this environment on the basis of the air quality index (AQI). The most abundant mineral particles were clay (53%), quartz (9%) and rock-forming minerals (<3%) sourced from roadside soil and fly ash from construction rock dust. Other particles such as clay+sulphate (17%), sulphur-rich particle (8%), soot (7%) and tarballs (8%) were generated from anthropogenic input from traffic-related activities. The highest average concentration of TRE such as Ba, Cd, La, Pb, V and Zn (2.81, 1.61, 1.21, 6.92, 8.92 and 10.73 respectively all in µg/m³) was observed in NHR, while those of Cu, Mo and Mn (5.45 µg/m³, 6.67 µg/m³ and 11.78 µg/m³ respectively) was observed in MR. Principal component analysis (PCA) revealed four factors (PC1 to PC4). In PC1 26.57% of the variability was observed and loaded with Ba (0.76), Pb (0.82), V (0.85) while PC 2 could explain 17.94% variability and had La (0.67), Mn (0.83) and Mo (0.68), PC 3 explained 15.91% variance loaded with Cd (0.84) and Zn (0.77), and PC 4 gave account of 13.83% of the variance and was loaded with Cu (0.86). PC1 and PC2 were products of both gasoline and diesel engine while PC3 and PC4 were generated from engine oil, brake and tyre wares. The calculated enrichment factor classified the TRE as being moderate to highly contaminated in both NHR and MR while RR was considered relatively uncontaminated.

Keywords: Traffic-related elements; Air quality index; National highway roads; Major roads; Rural roads

How to cite: Kolawole, O. T., Olatunji, A. S., and Fomba, K. W.: Particulate matter (PM10) concentration, mineralogical characteristics and traffic-related element (TRE) composition of urban traffic particles in Ibadan, Nigeria, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15274, https://doi.org/10.5194/egusphere-egu2020-15274, 2020.

Air pollution is a serious environmental issue and leading contributor to the disease burden in China. Following severe air pollution episodes during the 2012-2013 winter, the Chinese government has prioritised efforts to reduce PM_2.5 emissions, and established a national monitoring network to record air quality trends. Rapid reductions in fine particulate matter (PM_2.5) concentrations and increased ozone concentrations have occurred across China, during 2015 to 2017. We used measurements of particulate matter with a diameter < 2.5 µm (PM_2.5) and Ozone (O₃) from >1000 stations across China combined with similar datasets from Hong Kong and Taiwan to calculate trends in PM_2.5, Nitrogen Dioxide, Sulphur Dioxide and O₃ across the greater China region during 2015-2019. We then use the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) regional air quality simulations, to explore the drivers and impacts of observed trends. Using annually varying emissions from the Multi-resolution Emission Inventory for China, we simulate air quality across China during 2015-2017, and calculate a median PM_2.5 trends of -3.9 µg m^-3 year^-1. The measured nationwide median PM_2.5 trend of -3.4 µg m^-3 year^-. With anthropogenic emissions fixed at 2015-levels, the simulated trend was much weaker (-0.6 µg m^-3 year^-1), demonstrating interannual variability in meteorology played a minor role in the observed PM_2.5 trend. The model simulated increased ozone concentrations in line with the measurements, but underestimated the magnitude of the observed absolute trend by a factor of 2. We combined simulated trends in PM_2.5 concentrations with an exposure-response function to estimate that reductions in PM_2.5 concentrations over this period have reduced PM_2.5-attribrutable premature morality across China by 150 000 deaths year^-1.

How to cite: Silver, B., Conibear, L., Reddington, C., Knote, C., Arnold, S., and Spracklen, D.: Chinese emissions reductions deliver reduced PM2.5-caused mortality across China during 2015-2017, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19729, https://doi.org/10.5194/egusphere-egu2020-19729, 2020.

To meet public concerns of health caused by the high concentration of PM highly raised, this research has been done to find out unique physical, chemical, and optical characteristics of aerosols in the case of recent four years high PM concentration events over the East Asian region, especially in Korea and China. Severe air pollution over the East Asian region has occurred by the rapid development of urban areas and industrialization. Also, the meteorological conditions in East Asia are strongly correlated with a high concentration of air pollution and seasonal variation of aerosols. There are three types of aerosol properties (physical, chemical, and optical property), and each property is essential to understand the characteristics of regional and seasonal high PM concentrations. This research has been done to find out unique physical, chemical, and optical characteristics of aerosols in the case of high PM concentration events, especially in two super-mega cities (Seoul and Beijing) of Korea and China, by using various observations measured during recent four years. To analyze those characteristics of aerosols at high concentration events occur, various measurement data are used, like ambient surface air monitoring data (for physical properties) from national network in both Korea and China, Intensive Monitoring Data (for chemical properties), AERONET, GOCI satellite (for optical properties), and meteorological data during recent years (2015 – 2018). This study can provide observational evidence to confirm that each different region has different physical, chemical and optical characteristics of aerosol with the different time periods. The comprehensive results analyzed from this study and integrated methodologies suggested in this study might be useful to make a better in-depth understanding of the relations between various aerosol properties in certain regions and periods.

Key words : Aerosol, High concentration events, Physical/Chemical/Optical Properties of aerosols

How to cite: Cha, Y. and Song, C.-K.: Analysis of aerosol properties at recent (2015-2018) high PM concentration events in two super-mega cities, Seoul and Beijing, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20979, https://doi.org/10.5194/egusphere-egu2020-20979, 2020.

Delhi National Capital Region (NCR) is a well-known aerosol hotspot in the world, located in the western Indo-Gangetic Plain (IGP). Understanding the size and evolution of organic aerosol (OA) sources at NCR in winter period is very important due to their complexity in origin and processing.  High-Resolution Particle Time of Flight (HR-PToF) size distribution analysis is performed on the HR-ToF aerosol mass spectrometer (AMS) derived data at two sites, i.e., Indian Institute of Technology, Delhi (IITD) and Manav Rachna University, Faridabad (MRU) in NCR region to understand the size distribution and evolution of OA. Proxies of UMR sources of Hydrocarbon OA (m/z 57), Biomass burning OA (m/z 60), Semi volatile OA (m/z 43) and Low-volatile oxygenated OA (m/z 44) are selected to understand the size distribution of the isobaric high-resolution fragments at these proxies. The HR size distribution of primary and secondary fragments at these organic proxies shows relatively distinct mass distributions at lower and higher size bins. The diurnal variation of the mean modal diameters (MMD) of the HR fragments indicates that the C₄H₉⁺ (Hydrocarbon OA proxy) shows much diurnal variation in both the sites than the other proxies, where CO₂⁺ shows the least variation.

How to cite: M. Thamban, N., Lalchandani, V., Kumar, V., Mishra, S., Bhattu, D., Gates, J. S., Prevot, A., and Tripathi, S. N.: High-resolution size distributions of organic aerosol sources at two sites in Delhi National capital region (NCR) in Indo-Gangetic Plain, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21639, https://doi.org/10.5194/egusphere-egu2020-21639, 2020.

Despite ambitious efforts to abate surface air pollution, the air quality thresholds for PM10 and PM2.5 are regularly exceeded in the state of Styria. PM target levels are most frequently exceeded in industrial regions and urban cores of the forelands preceeding the alps. Besides local emissions, ambient meteorology and particularly stagnation are of special importance for PM pollution. Here we assess local and regional changes in PM pollution following emission reduction measures, while simultaneously considering effects of meteorological variability. We further supplement our observational study with a set of high-resolution chemistry-transport-model (CTM) simulations to assess future changes in the PM burden in Styria.

How to cite: Schmidt, C. A., Huszár, P., Mayer, M., Fritzer, J., and Rieder, H. E.: Variability of PM pollution in the light of emission changes and meteorological variability: a case study for Styria, Austria, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12358, https://doi.org/10.5194/egusphere-egu2020-12358, 2020.

Recently, the climatological and environmental communities have paid significant attention to the long-term trends and variations in haze-related weather conditions in North China (NC). This study investigates the issue based on a quantified air stagnation index (ASI_E) that combines the stagnation intensity with the background emissions, considering that haze occurrence strongly depends on the rate of emission. ASI_E shows a close spatial and temporal relationship with the observed PM_2.5 concentrations, and a strong sensitivity to haze occurrence in NC. The change in ASI_E revealed an approximate 19% increase in the annual stagnation intensity over the period of 1980-2018, due to significant decreases in PBLH and ventilation potency. The interannual variations in stagnation intensity were very significant. The percentage change of ASI_E was as high as 50-70% in some years. However, there was an apparent drop in stagnation intensity during 2013-2018, which possibly contributed to the recently reported improvement in aerosol concentration in NC. It also shows that such low-frequency oscillation occurred twice during 1980-2018. Hence, once the current trend of decreasing stagnation intensity changes, haze events may become more common in the future. Finally, we present a quick estimate for the emission reduction ratio that can balance the variations and trend of stagnation intensity using a simple linear model, which can be used to evaluate the difficulty of the “clean air challenge” in NC. The results suggest that the enforcement of the emission reduction plan should be tailored according to the stagnation conditions in the case study year and region.

How to cite: Feng, J.: Long-term trends and variations in haze-related stagnation intensity in North China during 1980-2018, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3780, https://doi.org/10.5194/egusphere-egu2020-3780, 2020.

We have investigated the impact of the polar jet on the winter PM₁₀ (particulate matter with aerodynamic diameter ≤ 10 μm) concentrations in Europe during a 10-year period. For this purpose, we have computed the daily latitude and strength of the jet by using reanalysis wind fields in the lower troposphere over the eastern North Atlantic (0°–15° W). Then we have extracted daily average surface PM₁₀ observations at ~440 sites from the European air quality database (AirBase).

Four preferred jet positions have been identified over the 0°–15° W sector in winter: southern (south of 41° N), central-southern (between 41° N and 51° N), central-northern (between 51° N and 63° N) and northern (north of 63° N). They exert a stronger influence than the jet strength on the mean PM₁₀ levels. Consequently, we have examined whether the full distribution of PM₁₀ and the occurrence of PM₁₀ extremes (exceedances of the local winter 95th percentiles) are also linked to the jet position.

The northern position is associated with enhanced PM₁₀ concentrations (on average ~9 μg m⁻³ above the mean values) and threefold increases in the odds of PM₁₀ extremes over northwestern / central Europe. Comparable increases have been found in southern Europe when the jet is in its central-northern position. In both cases, the rise in the PM₁₀ concentrations is associated with blocking of the zonal flow over those regions and the impact on PM₁₀ extremes is maximised for time lags of around 1–2 days. On the other hand, the mean sea level pressure (SLP) patterns of the central-southern jet position resemble a positive phase of the winter North Atlantic Oscillation (NAO), yielding large PM₁₀ decreases (on average around −9 μg m⁻³) in northwestern / central Europe. Similarly, the southern jet position results in low PM₁₀ concentrations in southern Europe.

These results demonstrate that winter near-surface PM₁₀ concentrations in Europe are strongly sensitive to the jet latitude, with implications for future projections of air pollution. As there is no consensus on the future evolution of the North Atlantic jet in a warming climate, different responses among model simulations could be relevant to understand discrepancies in their climate change projections of PM₁₀ and other pollutants.

How to cite: Ordóñez, C., Garrido-Perez, J. M., García-Herrera, R., and Barriopedro, D.: Linking the variability of PM10 in Europe to the position of the extratropical jet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3129, https://doi.org/10.5194/egusphere-egu2020-3129, 2020.

The change in PM level is the combined result of meteorological change and emission control. Meteorological change can strengthen or weaken the effectiveness of emission control. We applied an empirical and a statistical method to understand the effect of the meteorological variables on high PM2.5 event. A major meteorological mode associated with synoptic weather pattern that governs the high PM2.5 concentration in Seoul was identified through the empirical synoptic weather pattern classification and principal component analysis and regression. We used 2016-2018 PM2.5 observations from ~110 sites and 1 surface meteorological observation and 1 radiosonde observation within Seoul Metropolitan Area (SMA). Fifty cases with high PM2.5 concentration in SMA were selected in 2016 for the empirical weather pattern classification, and observed PM2.5 and meteorological data during 2017 ~ 2018 for the principal component analysis and regression.

As a result, a total of six synoptic weather patterns were derived, which was in agreement with the dominant meteorological mode of principal component analysis and regression. The dominant meteorological consists of high temperature at 850hPa, high geopotential height at 500hPa, high surface temperature, low wind speed at both surface and 850 hPa. The meteorological modes associated with the six patterns account for more than 90% of all high PM2.5 pollution days. Our results suggest that major synoptic weather modes can be used to easily predict high dust concentration potentials compared to WRF-SMOKE-CMAQ based air quality forecasting models.

How to cite: chang, L., hong, H., and kim, C.: To what extent can the synoptic weather explain high PM2.5 pollution in Seoul?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13585, https://doi.org/10.5194/egusphere-egu2020-13585, 2020.

Despite frequent haze pollution in China in recent years, our knowledge of regional pollution episodes associated with air transport and synoptic weather systems is limited. In this study, we conducted two intensive campaigns simultaneously to measure the highly time-resolved chemical composition of fine particles (PM_2.5) in suburban Shanghai and Nanjing during the winter of 2017 and the summer of 2018. The average PM_2.5 mass concentrations were 53.9 (65.7) µg m^-3 and 32.8 (37.3) µg m^-3 in Shanghai (Nanjing) in winter and summer, respectively. In winter, extreme haze episodes were observed synchronously with enhanced contributions of nitrate at both sites and of low-volatile oxidized organic aerosol (LV-OOA) in Shanghai. Long-range transport from Northern China was demonstrated to play an important role in the episodes, which occurred simultaneously at both sites. Influenced by the cold fronts, Nanjing had a relatively longer pollution duration, whereas Shanghai exhibited faster PM increases. In summer, air masses passing though the city-clusters of the YRD were responsible for the pollution episodes. Low wind speeds, which favored the accumulation of primary aerosols, and strong photochemical activity indicated by high ozone level, which promoted the formation of secondary aerosols, resulted in elevated contributions of nitrate, Hydrocarbon-like organic aerosol (HOA) and semi-volatile oxidized organic aerosol (SV-OOA) to PM in Shanghai. In addition, a pollution episode dominated by increases of nitrate and organic aerosols was observed in Nanjing two days later despite the clean situation in Shanghai. Our results highlight the importance of regional or sub-regional emission control to mitigate haze pollution in city clusters, such as the YRD in Eastern China.

How to cite: Sun, P.: Impact of air transport and secondary formation on haze pollution in the Yangtze River Delta: In situ online observations in Shanghai and Nanjing, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1971, https://doi.org/10.5194/egusphere-egu2020-1971, 2020.

Key Words:
Air Quality; Air Pollution Monitoring; Low-Cost Sensors; Reference Methods, Microsensors, Experimental Campaign
 
Abstract:

Air quality in the Middle East (ME) is strongly affected by desert dust besides anthropogenic pollutants. The health hazards associated with particulate matter (PM) are the most severe in this desert region. The enhancement of Air quality monitoring is needed to implement abatement strategies and stimulate environmental awareness among citizens. Several techniques are used to monitor PM concentration. The air quality monitoring stations (AQMS) equipped with certified instrumentation is the most reliable option. However, AQMSs are quite expensive and require regular maintenance. Another option is low-cost sensors (LCS) that seen as innovative tools for future smart cities. They are cost-effective and allow to increase the spatial coverage of air-quality measurements as the number of conventional AQMS is generally quite small, so the current density of the monitoring stations in the Middle East is low.

In this work, we evaluated the PM air-quality climatology in the major cities in Saudi Arabia (Jeddah, Riyadh, and Dammam) for four years between 2016 and continued until 2020. We used the measurement data that were conducted by the Saudi Authority for Industrial Cities and Technology Zones (MODON) using certified reference AQMS installed inside the suburban areas of the three major cities in Saudi Arabia. Also, we tested the performance of the five LCS systems for eight months, starting in May 2019 and continued until January 2020. For this purpose, we set AQMS with the PM reference instrumentation (based on beta-ray absorption) side-by-side with five different LCS systems (based on light scattering) in the industrial part of Jeddah city. We collected, filtered, validated PM data, and applied standard measurement and calibration procedures.

The AQMS measurements show that in Summer, the daily mean PM concentrations exceed the World Health Organization (WHO) limits for PM2.5 and PM10 almost every day in Jeddah, Riyadh, and Dammam. The WHO limits are also frequently violated in the winter months. The AQMS measurements reliably show dust storm spikes when PM pollution is extremely high while all the LCSs fail to capture these severe events. We found that LCS and AQMS PM measurements are poorly correlated in Summer, but show slightly better results in fair-weather Winter days when humidity and temperature are low. But they still cannot capture severe dust events.

How to cite: Alshehri, Y., Alghamdi, M., Khoder, M., Almehmadi, F., Bamuneef, A., Moathen, R., and Stenchikov, G.: Particulate Monitoring and Evaluation of the Low-cost Sensors Performance at the Middle East, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2972, https://doi.org/10.5194/egusphere-egu2020-2972, 2020.

Air pollution and climate change represent today key environmental issues. They are highly linked each other through various ways. Pollutant emission reductions can improve both air quality and mitigate the climate changes. On the other hand, heavy precipitations and/or an increased frequency of their occurrence (climate change) might help to clean the air from pollutants. Despite of the scientific progress, the understanding of atmospheric pollutant wet removal in urban and peri-urban areas is still subject to a large uncertainty. Among factors of uncertainties are aerosol large variability, different sources, aerosol-cloud processing.

This study examines how the concentrations of particulate matter with an aerodynamic diameter below 10 μm (PM₁₀) and below 2.5 μm (PM_2.5) might be linked with precipitation characteristics using an observational data set for three years (2015-2017) in Bucharest metropolitan area. Particulate matter data and meteorological parameters at each site (atmospheric pressure, relative humidity, temperature, global solar radiation, wind speed and direction) were extracted from the public available Romanian National Air Quality Database. Meteorology was complemented with radar products (images, reflectivity, echotops) from the C-band meteorological radar from National Meteorological Administration in Bucharest. Change of aerosol mass concentration during the evolution of the precipitation events was investigated. The aerosol scavenging coefficients were estimated and compared with those in scientific literature. Correlations between meteorological parameters and ambient PM₁₀ and PM_2.5 levels were analyzed. Connection of meteorological phenomena occurrence and air mass origin was investigated by computing air mass backward trajectories using the HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory) model for 72 hours back.

It was found that heavy precipitations have a strong influence on the atmospheric aerosol concentrations, determining an increased value of scavenging coefficient with up to one order of magnitude higher than in case of a moderate precipitation. Higher values of scavenging coefficient than in literature reveals a good capability of the convective precipitating systems to clear the atmosphere from aerosol and pollutant species.

The obtained results are important for modeling of air quality and for investigations of aerosol wet deposition processes.

Acknowledgement:

The authors thank the financial support from UB198/Int project and to National Meteorological Administration for access to the RADAR database. The data regarding ground-based air pollution and meteorology by site was extracted from the public available Romanian National Air Quality Database, www.calitateaer.ro, last accessed in December 2019.

How to cite: Hriscan, T., Burcea, S., and Iorga, G.: Link between precipitations and air quality in Bucharest Greater Area, Romania, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2722, https://doi.org/10.5194/egusphere-egu2020-2722, 2020.

In the review compiled by Monks et al. (2015), it is noted that the main variations in the tropospheric ozone are determined by the exchange between the troposphere and the stratosphere, in-situ photochemical production from gaseous precursors depending on their composition and concentration, solar radiation income, and meteorological conditions. The impact of precipitation on the surface ozone concentration is a less well-studied factor.

The process of ozone interaction with precipitation was studied theoretically (Heicklen, 1982). Two ways of the above process were analyzed: adsorption of gas molecules on the surface of a particle and a chemical reaction with its surface. There are no direct data on the verification of these findings in the literature. At the same time, there is some evidence of a possible link between precipitation and ozone.

This study is aimed to analyze the presence or absence of changes in the ozone concentration during precipitation. Variations of the surface ozone concentration (SOC) in the presence of precipitation were analyzed using the long-term data obtained at the TOR-station established in 1992 for ozone monitoring in Tomsk. It was revealed that these changes can be both positive (increase in concentration) and negative. The sharp changes in the SOC are observed when frontal precipitation takes place. In the presence of air-mass precipitation, the sign and magnitude of the change is determined by the diurnal variation of ozone concentration.

The analysis showed a coincidence of the SOC growth during precipitation with its increase in diurnal variation in 59% of cases. The coincidence in the wave of the concentration decline in the diurnal variation with decreasing precipitation rate is even higher and amounts to 85%.

Airborne sounding carried out in the vicinity of the TOR-station shown that in a number of cases the ozone deposition from the boundary layer is observed upon the transition of thermal stratification during the precipitation to neutral.

Monks P. S, Archibald A. T., Colette A., Cooper O., Coyle M., Derwent R., Fowler D., Granier C., Law K. S., Mills G. E., Stevenson D. S., Tarasova O., Thouret V., von Schneidemesser E., Sommariva R., Wild O., Williams M. L. Tropospheric ozone and its precursors from the urban to the global scale from air quality to short-lived climate forcer. Atmos. Chem. Phys., 2015, v.15, N15, p.8889–8973.

Heicklen J. The Removal of Atmospheric Gases by Particulate Matter. In Heterogeneous Atmospheric Chemistry, ed. D. R. Schryer, Geophysical Monograph 26. American Geophysical Union, Washington, DC, USA, 1982, p. 93-98.

How to cite: Ptashnik, I. V., Belan, B. D., Savkin, D. E., Tolmachev, G. N., Sklyadneva, T. K., Rasskazchikova, T. M., Arshinova, V., and Fofonov, A. V.: Variation of the surface ozone concentration during precipitation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6862, https://doi.org/10.5194/egusphere-egu2020-6862, 2020.

As the production of ozone in surface air is determined by ambient temperature and by the prevalent chemical regime, a very different temperature dependence of ozone production emerges for NO_x and VOC limited regions. In this study we evaluated the temperature sensitivity of ozone production for rural, suburban as well as urban sites in Austria on seasonal basis. The analysis is based on observational data from Austrian monitoring networks for the time period spanning 1990 – 2018. Surface ozone, nitrogen oxides (NO_x), daily sums of global radiation and minimum daily temperature are used as covariates in our study. The observed NO_x to VOC ratio at individual sites is variable over time due to changes in precursor emissions and/or the variability of meteorological parameters such as mixing layer height. At the site level we relate the temperature sensitivity of ozone production to the daily mean NO_x mixing ratio and the daily minimum temperature. This information allows us to determine the impact of past/future temperature changes on surface ozone  abundance in the context of reductions of NO_x emissions and changing methane backgrounds.

How to cite: Mayer, M., Staehle, C., Schmidt, C., and Rieder, H. E.: Changes in the temperature sensitivity of surface ozone production: a case-study based on long-term observations in Austria, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10337, https://doi.org/10.5194/egusphere-egu2020-10337, 2020.

Daily maximum temperature is known to be the meteorological variable that mostly controls the afternoon near-surface ozone concentrations during summer. Air stagnation situations, characterised by stable weather conditions and poor ventilation, also lead to the accumulation of pollutants and regional ozone production close to the surface. This work evaluates the joint effect of daily maximum temperature and a simplified air stagnation index on surface ozone observations in eight regions of Europe during summer 1998-2015.

As expected, the correlations of MDA8 O₃ (maximum daily 8-h running average ozone) with temperature are higher than with stagnation for most regions. Nevertheless, stagnation can also be considered as a good predictor of ozone, especially in the regions of central/southern Europe, where the correlation coefficients between MDA8 O₃ and the percentage of stagnant area are within the range 0.50–0.70. MDA8 O₃ consistently increases over central/southern Europe under stagnant conditions, but this is not always the case in the north. Under non-stagnant conditions and daily maximum temperatures within 20-25 ºC (typical temperatures of fair weather conditions that allow photochemical production), northern Europe is affected by southerly advection that often brings aged air masses from more polluted areas, increasing the MDA8 O₃ mixing ratios.

We have also found that the ozone diurnal cycles in the central/southern regions exhibit large amplitudes, with above-average daytime and below-average night-time concentrations, when stagnation occurs. Stagnant nights are often associated with stable shallow planetary boundary layer and, presumably, enhanced dry deposition and chemical destruction of ozone. After sunrise, mixing with air from air from the residual layer, accumulation of ozone and precursors, and photochemical production seem to be the main mechanisms involved in the build-up of daytime ozone.

According to previous studies, some of the central/southern European regions where stagnation has a clear impact on ozone have undergone significant upward trends in air stagnation in the past and are also likely to experience increases in the future. However, our study has identified other regions with unclear responses of summer ozone to the occurrence of stagnation. This indicates that climate model projections of increases in stagnation should not directly be translated into enhanced summer ozone pollution if the sensitivity of this pollutant to stagnation has not been proved for a particular region.

How to cite: Garrido-Pérez, J. M., Ordóñez, C., García-Herrera, R., and Schnell, J. L.: The differing impact of air stagnation on near-surface ozone across Europe, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9213, https://doi.org/10.5194/egusphere-egu2020-9213, 2020.

Ambient ozone (O₃) remains a serious air pollution problem (O₃) of Northern Hemisphere, and still represents a considerable threat both for human health and ecosystems. In Europe, the critical levels of O₃ are permanently exceeded over vast areas (EEA, 2019). In the Czech Republic (CR), monitoring of O₃ has been operated since 1993, currently at 50 sites, including both rural and urban stations covering the country (CHMU, 2019). O₃ exposures in the CR are relatively high (Hůnová, Schreiberová, 2012; Hůnová et al., 2016), and may result in negative endpoints, both regarding human health (Hůnová et al. 2013) and vegetation (Hůnová et al., 2011). O₃ is highly meteorology dependent and shows considerable year-to-year variations (Hůnová et al., 2019 a, b). Two to three-decade time series allows for a sound trend analysis, hence O₃ concentrations for trends at Czech long-term monitoring sites were already analysed using Mann-Kendall non-parametric test (Hůnová, Bäumelt, 2018).

This time, however, our approach for time analysis was different. We applied a generalized additive model, GAM (Wood, 2017; Hastie & Tibshirani, 1990) framework as a flexible, semiparametric regression approach to address nonlinear trend shapes in a formalized and unified way. In particular, we employed penalized spline approach with cross-validated penalty coefficient estimation.  We have examined daily mean O₃ concentrations measured at twelve Czech sites representing different environments, geographical areas, and altitudes across the country; four urban, for rural and four mountain sites. We used long-term data series from the time period of 1994–2018.

Our results show inconsistent behaviour of sites before 1998 when the strict emission limits were introduced with an immediate consequence of substantial decrease in O₃ precursor emissions. The highest concentrations and the most dynamic O₃ decrease in this time period was recorded at the Praha 4-Libus urban background site, the lowest concentrations and the steepest increase in O₃ were recorded at the Rudolice mountain site in the former Black Triangle Area. Two local maxima – around 2003 for some sites and 2006 for other sites – and a local minimum around 2013 are indicated. Steady increase in O₃ concentrations for all sites is evident after 2014 up to now, most likely due to recent five hot and dry summer seasons. Seasonal O₃ course averaged for the entire measuring period is similar for all sites, with clear maximum in May-June. The highest O₃ in summer and lowest in winter were observed at the Usti nad Labem-Kockov site, relatively most flat curve, with the least differences between summer and winter was recorded at the Churanov site, in the Sumava Mts. More interesting is to compare the seasonal O₃ curves for individual years.

In contrast with Mann-Kendall test standardly used for this kind of analysis, the GAM approach offers a detailed view on both time trend and seasonality curve and facilitates the analysis and interpretation of the results.

How to cite: Hunova, I., Brabec, M., and Malý, M.: Trends in ambient ozone concentrations at twelve sites of the Czech Republic over the past three decades, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6973, https://doi.org/10.5194/egusphere-egu2020-6973, 2020.

Tropospheric ozone is a major pollutant and a short-lived greenhouse gas and has therefore attracted much concern in recent years. The ozone concentration in the troposphere and lower stratosphere over Beijing has been observed since 2002 by ozonesondes developed by the Institute of Atmospheric Physics. We used these balloon-based observations to analyze the long-term variability of ozone over Beijing during the whole period from 2002 to 2018. The ozonesondes measured increasing concentrations of ozone from 2002 to 2012 in both the troposphere and lower stratosphere. There was a sudden decrease in observed ozone between 2011 and 2012. After this decrease, the increasing trend in ozone concentrations slowed down, especially in the mid-troposphere, where the positive trend became neutral. We used the Chemical Lagrangian Model of the Stratosphere (CLaMS) to determine the influence of the transport of ozone from the stratosphere to the troposphere on the observed ozone profiles. Because there is no tropospheric chemistry in CLaMS, the sudden decrease simulated by CLaMS indicates that a smaller downward transport of ozone from the stratosphere after 2012 may explain a significant part of the observed decrease in ozone in the mid-troposphere and lower stratosphere. However, the influence of stratospheric ozone in the lower troposphere is negligible in CLaMS and the hiatus in the positive trend after 2012 can be attributed to a reduction in ozone precursors as a result of stronger pollution control measures in Beijing.

How to cite: Zhang, Y., Tao, M., Zhang, J., Liu, Y., Chen, H., Cai, Z., and Konopka, P.: Long-term Variations in Ozone Levels over Beijing: Observations and Model Simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3839, https://doi.org/10.5194/egusphere-egu2020-3839, 2020.

This study highlights a previously under-appreciated “climate penalty” feedback mechanism - namely, substantial reductions of ozone uptake by water stressed vegetation – as a missing piece to the puzzle of why European ozone pollution episodes have not decreased as expected in recent decades, despite marked reductions in regional emissions of ozone precursors due to regulatory changes. The most extreme ozone pollution episodes are linked to heatwaves and droughts, which are increasing in frequency and intensity over Europe, with severe impacts on natural and human systems. Under drought stress, plants close their stomata to reduce water loss, consequently limiting the ozone uptake by vegetation (a component of dry deposition), leading to increased surface ozone concentrations. Such land-biosphere feedbacks are often overlooked in prior air quality projections, owing to a lack of process-based model formulations. Here, we use six decades of observations and Earth system model simulations (1960-2018) with an interactive dry deposition scheme to show that declining ozone removal by water-stressed vegetation in the warming climate exacerbate ozone air pollution over Europe. Incorporated into a dynamic vegetation land – atmospheric chemistry – climate model, the dry deposition scheme mechanistically describes the response of ozone deposition to atmospheric CO₂ concentration, canopy air vapor pressure deficit, and soil water availability. Our observational and modeling analyses reveal drought stress causing as much as 70% reductions in ozone removal by forests. Reduced ozone removal by water-stressed vegetation worsens peak ozone episodes during European mega-droughts, such as the 2003 event, offsetting much of the air quality improvements gained from regional emission controls. Accounting for vegetation feedbacks leads to a three-fold increase in high surface ozone events above 80 ppbv (8-hour average) and a 20% increase in the sensitivity of ozone pollution extremes (95^th percentile) to increasing temperature. As the frequency of hot and dry summers is expected to increase in the coming decades, this ozone climate penalty could be severe and therefore needs to be considered when designing clean air policy in the European Union. 

Notes: This study is currently under review for possible publication in Nature Climate Change. 

How to cite: Lin, M., Horowitz, L., Xie, Y., Paulot, F., Malyshev, S., Shevliakova, E., Finco, A., Gerosa, G., Kubistin, D., and Pilegaard, K.: Vegetation feedbacks during drought exacerbate ozone air pollution extremes in Europe, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12605, https://doi.org/10.5194/egusphere-egu2020-12605, 2020.

The Tropospheric Ozone Assessment Report, phase 2, (TOAR-II) database is a collection of global ground-level ozone in-situ measurements from various locations. It also holds data of selected ozone precursors and meteorological variables. TOAR-II assembles air quality data from many different sources and thus requires a common data quality assessment (QA) to ensure the data meet the quality required for globally consistent analyses. The large volume of this database (more than 100,000 data series) enforces the use of automated, data-driven QA procedures.

Accordingly, we have developed a statistical model for automated QA. This model consists of several statistical tests that are classified into several sub-groups. In this model, a QA-score (an indicator ranging from 0 to 1) was assigned to each individual data point to estimates the value‘s plausibility. The foundation of this concept is statistical hypothesis testing and the probability theory. This model was implemented in a Python package and is called AutoQA4Env.

One application of AutoQA4Env is the data ingestion workflow of TOAR-II. The tool generates a data quality report which is then sent back to the data provider for inspection. Since AutoQA4Env is easily configurable, it allows the users to set quality thresholds and thus filter data according to their use case. While we primarily develop AutoQA4Env for air quality data, the same concept and model might be applicable to other databases and the software framework is flexible enough to allow for other use cases.

How to cite: Kaffashzadeh, N., Chang, K.-L., Schröder, S., and Schultz, M. G.: A Statistical Model for Automated Quality Assessment of the TOAR-II, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13357, https://doi.org/10.5194/egusphere-egu2020-13357, 2020.

Effect of photochemically active species emissions on near-surface air composition in industrial regions is non-local and in many cases can be traced in transcontinental scale. Largescaled plumes of polluted air defined by observations of tracer species on background stations and calculations with chemical-transport models are examples of this effect. In this work we use GEOS-Chem chemical transport model to make an assessment of influence have anthropogenic and biogenic emissions in Europe, European territory of Russia (ETR) and Siberia on total ozone generation taking into account common non-linear properties of O₃–NO_x–СО–VOC system. It is shown that increasing of ozone production rate due to regional anthropogenic emissions of NO_x leads to substantial (up to 20 ppbv) increase of near-surface ozone concentrations in mid-latitudes traced up to 120E. The predominant role of long-range air transport against regional sources of photochemical ozone production was determined for the most part of European Russia and Siberia.
We also make a numerical assessment of ozone balance in Europe, ETR and Siberia. Annual ozone total mass in lower troposphere (from surface to 800 hPa) for Europe, ETR and Siberia depending on region is 1.5–2.4 Tg in warm period (1 April – 30 September) and 1.3–2.2 Tg in cold period (1 October - 31 March). Ozone production in chemical processes with a high degree of accuracy (about 99%) is balanced by total atmospheric transport, while absolute variations in O₃ total mass do not exceed 0.5 Tg/year in Europe and 0.4 Tg/year in Siberia.
This work was supported by the Russian Foundation for Basic Research under grant 18-35-20031.

How to cite: Shtabkin, Y., Moiseenko, K., Skorokhod, A., and Berezina, E.: Long-range air transport in Northern Eurasia: Seasonal ozone variations and implications for regional ozone budget, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14701, https://doi.org/10.5194/egusphere-egu2020-14701, 2020.

The puy de Dôme (pdD) altitude research station is located in the centre of France (45° 46' N, 2° 57' E, 1465 m altitude a.s.l), 16 km from the town of Clermont-Ferrand. This station is a global GAW station (PUY), and is part of the ACTRIS-2 integrating activities (H2020). Long series of meteorological parameters such as wind speed and direction, temperature, pressure, relative humidity and radiation, atmospheric trace gases (O₃, NO_x, SO₂, CO₂, CO), and physical, optical and chemical properties of aerosols (particle size, black carbon, mass,..) are available.

Cartridge sampling measurements are performed to link the observations of volatile organic compounds (VOCs) within ACTRIS and GAW. A selection of VOCs, including a large set of non-methane hydrocarbons and some terpenes (isoprene, α-pinene), was measured during summer 2010, spring and summer 2011, winter 2012, summer and winter 2013, summer 2015, and twice a week in 2017, 2018 and 2019. The analysis of VOCs collected off-line on Tenax/Carbosieve III or Tenax TA cartridges was carried out using gas chromatography coupled with thermo-desorption with mass spectrometry (GC-MS).

In August 2018, a new gas chromatography (GC-FID) system was installed at the station. It allows the acquisition of non-methane hydrocarbons (C₅-C₁₀) with a temporal resolution of two hours.

The reactive gas measurement series are analysed in terms of observed levels (i), diurnal and seasonal variability (ii), air mass origins (iii) and sources of these gaseous pollutants (iv).

(i) The level observed at the PUY station is discussed and compared with two other stations: Monte Cimone (mainly in the free troposphere) and Hohenpeissenberg (mainly in the planetary boundary layer PBL).

(ii) As the height of the PBL changes with a diurnal cycle and with the seasons, the PUY station is in the different layers of the troposphere during the year impacting the measured concentrations.

(iii) In order to determine the transport pathways of the air masses before their arrival at the pdD site, the HYSPLIT (Hybrid Single Particle Lagrangian Trajectory) model was used. Trajectories were classified according to their predominant transport direction prior to measurement, either continental (C), marine (M), modified marine (Mod), Mediterranean (Med), or mixed according to their trajectories. In order to determine the influence of wind direction, the pollution wind rose was determined for the main pollutants.

(iv) Comparison with temperature, air mass origins, boundary layer height are used to identify the main parameters influencing the variability of VOCs. The Principal Component Analysis (PCA) has been performed to deduce correlations between the main atmospheric species and their main determinants.

How to cite: Colomb, A., Rocco, M., Borbon, A., Yu, Y., Wang, M., Bouvier, L., Pichon, J.-M., Ribeiro, M., Deguillaume, L., and Baray, J.-L.: Long-term observations of reactive gases at the puy de Dôme (PUY Global GAW) station (France, 1465 m a.s.l.), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20033, https://doi.org/10.5194/egusphere-egu2020-20033, 2020.

Given the importance of tropospheric ozone as a greenhouse gas and a hazardous pollutant that impacts human health and ecosystems, it is critical to quantify and understand long-term changes in its abundance.  Satellite records are beginning to approach the length needed to assess variability and trends in tropospheric ozone, yet an intercomparison of time series from different instruments shows substantial differences in the net change in ozone over the past decade.  We discuss our efforts to produce Earth Science Data Records of tropospheric ozone and quantify uncertainties and biases in these records.  We also discuss the role of changes in the magnitude and distribution of precursor emissions and in downward transport of ozone from the stratosphere in determining tropospheric ozone abundances over the past 15 years.

How to cite: Neu, J., Miyazaki, K., Bowman, K., and Osterman, G.: Quantifying and attributing changes in tropospheric ozone from a combination of satellite measurements and models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21123, https://doi.org/10.5194/egusphere-egu2020-21123, 2020.

Trace gases and aerosols in the troposphere exhibit significant variability, particularly so over regions where biomass burning occurs, and downwind of both biomass burning and large urban areas. Knowledge and quantification of the mean, trends, and most importantly variance over these source regions and their downwind plumes over climatological scales can therefore be used to retrieve information about both the source amounts as well as the amounts transported.

In this work, we pinpoint a way to separate these regions from one another by simultaneously employing a variance maximization approach to global weekly column measurements of OMI NO₂ (which has a very short atmospheric lifetime) and MOPITT CO (which has a relatively long atmospheric lifetime) from the past decade and a half. The variance maximization is done using the EOF/PCA approach, and yields important results in northern Australia, Indonesia, northern Southeast Asia, Siberia, central and southern Africa, Amazonia and California. We then compare and contrast the spatial and temporal results in terms of the difference in the atmospheric lifetime of the co-emitted species. We specifically look for an overlap between the two over the source regions, and a strong signal in CO exclusively over both the source and downwind transport regions.

This technique improves upon the current generation of bottom-up techniques detecting land-use change and hotspots, in terms of offering higher temporal resolution and better representations under cloud cover. However, to further improve the work, we hope to employ AOD measurements to refine our results, as co-emitted aerosols like BC are sensitive to precipitation, and thus able to pick up the source and transport under different precipitation conditions.

How to cite: Deng, W. and Cohen, J.: Using Variance Maximization with Multi-species Measurements to Pinpoint the Sources and Long Range Transport of Biomass Burning over the Past 15 Years, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13533, https://doi.org/10.5194/egusphere-egu2020-13533, 2020.

Aromatic compounds in the troposphere are reactive towards ozone
(O₃), hydroxyl (OH) and other radicals. Here we present an
assessment of their impacts on the gas-phase chemistry, using the
general circulation model EMAC (ECHAM5/MESSy Atmospheric Chemistry). The
monocyclic aromatics considered in this study comprise benzene, toluene,
xylenes, phenol, styrene, ethylbenzene, trimethylbenzenes, benzaldehyde
and lumped higher aromatics bearing more than 9 C atoms. On a global
scale, the estimated net changes are minor when aromatic compounds are
included in the chemical mechanism of our model. For instance, the
tropospheric burden of CO increases by about 6 %, and those of OH,
O₃, and NO_x (NO + NO₂) decrease between
2 % and 14 %. The global mean changes are small partially because of
compensating effects between high- and low-NO_x regions. The
largest change is predicted for glyoxal, which increases globally by 36
%. Significant regional changes are identified for several species. For
instance, glyoxal increases by 130 % in Europe and 260 % in East Asia,
respectively. Large increases in HCHO are also predicted in these
regions. In general, the influence of aromatics is particularly evident
in areas with high concentrations of NO_x, with increases up
to 12 % in O₃ and 17 % in OH. Although the global impact of
aromatics is limited, our results indicate that aromatics can strongly
influence tropospheric chemistry on a regional scale, most significantly
in East Asia.

How to cite: Sander, R., Cabrera-Perez, D., Bacer, S., Gromov, S., Lelieveld, J., Taraborrelli, D., and Pozzer, A.: Impacts of monocyclic aromatics on regional and global tropospheric gas-phase chemistry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5114, https://doi.org/10.5194/egusphere-egu2020-5114, 2020.

Ecosystems and human health are directly affected by atmospheric ammonia, by unbalancing the vegetation nutrient cycle and causing respiratory troubles both directly and through the formation of fine particles. In Europe, agricultural practices are the dominant source of atmospheric ammonia. It is released to the atmosphere by volatilization of fertilizer applied to soils and decay of organic matter. Then, it reacts with acids (such as sulphuric, nitric and chlorine acids) or nitrogen oxides (all produced in high concentrations from anthropogenic activities) to produce ammonium aerosols, whose concentrations over Europe and Paris megacity are particularly high during springtime pollution events, as occurred in 2014 and 2015.

Difficulties for measuring ammonia by in situ techniques are induced by its polarity, which causes accumulation in inlets and sampling tubes. Remote sensing is therefore a valuable alternative method to measure ammonia, without direct interaction with the sample. Measurements of ammonia total atmospheric columns using the OASIS observatory are routinely made in the Paris suburbs since 2009 using a medium spectral resolution BRUKER Fourier transform infrared spectrometer. Spectra of radiation emitted by the sun and absorbed by the atmosphere were recorded every 10 minutes, under clear sky conditions, enabling the observation of the diurnal evolution of ammonia concentrations.

Our work provides a new analyse of the diurnal evolution of ammonia over the Paris megacity during springtime pollution events. For this, we use measurements of total atmospheric columns of ammonia derived from the ground-based OASIS observatory for the first time and from satellite approaches, such as that from IASI and other available satellites. Furthermore, this study takes into account the influence of meteorological conditions and atmospheric chemical composition, of gaseous and particulate phases, from surface measurements simultaneously performed at Palaiseau, in the Paris region.

How to cite: Kutzner, R. D., Cuesta, J., Chelin, P., Petit, J.-E., Hase, F., Orphal, J., Blumenstock, T., Schneider, M., Viatte, C., and Clerbaux, C.: Analysis of the diurnal evolution of atmospheric ammonia over the Paris megacity from ground-based and satellite remote sensing , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9238, https://doi.org/10.5194/egusphere-egu2020-9238, 2020.

Nitrous acid (HONO), an important precursor of the hydroxyl radical (OH), has long been recognized as of significance to atmospheric chemistry, but its sources are still debated. In this study, we conducted continuous measurement of HONO from November 2017 to November 2018 at the SORPES station in Nanjing of eastern China. The yearly average mixing ratio of observed HONO was 0.69±0.58 ppb, showing a larger contribution to OH relative to ozone with a mean OH production rate of 1.16 ppb h⁻¹. To estimate the effect of combustion emissions of HONO, the emitted ratios of HONO to NO_x were derived from 55 fresh plumes (NO∕NO_x > 0.85), with a mean value of 0.79 %. During the nighttime, the chemistry of HONO was found to depend on RH, and the heterogeneous reaction of NO₂ on an aerosol surface was presumably responsible for HONO production. The average nighttime NO₂-to-HONO conversion frequency (C_HONO) was determined to be 0.0055±0.0032 h⁻¹ from 137 HONO formation cases. The missing source of HONO around noontime seemed to be photo-induced, with an average P_unknown of 1.04 ppb h⁻¹, based on a semi-quantitative HONO budget analysis. An over-determined system of equations was applied to obtain the monthly variations in nocturnal HONO sources. Besides the burning-emitted HONO (accounting for about 23 % of the total concentration), the contribution of HONO formed heterogeneously on ground surfaces to measured HONO was an approximately constant proportion of 36 % throughout the year. The soil emission revealed clear seasonal variation and contributed up to 40 % of observed HONO in July and August. A higher propensity for generating HONO on aerosol surfaces occurred in severe hazes (accounting for 40 % of the total concentration in January). Our results highlight ever-changing contributions of HONO sources and encourage more long-term observations to evaluate the contributions from varied sources.

How to cite: Liu, Y.: Semi-quantitative understanding of source contribution to nitrous acid (HONO) based on 1 year of continuous observation at the SORPES station in eastern China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8791, https://doi.org/10.5194/egusphere-egu2020-8791, 2020.

Air pollution has become one of the major environmental problems around the world. It is particularly serious in China due to the rapid development of the economy and industrialization. Four ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) were performed in four metropolises of China during 2019. Beijing, Nanjing, Guangzhou and Chongqing are central cities of Beijing-Tianjin-Hebei region, Yangtze River Delta, Pearl River Delta and Sichuan basin, four major polluted areas of China, respectively. In this study, vertical profiles of aerosol extinction coefficient, nitrogen dioxide (NO₂) in these four cities were retrieved from MAX-DOAS. In order to understand the pollution characteristics in four major polluted areas during 2019, the averaged diurnal variation and seasonal variation of aerosol and NO₂ in above four cities were performed. On the other hand, the differences of vertical structure of aerosol and NO₂ in four cities were analyzed. In addition, the variation of PM_2.5, PM₁₀ and PM_2.5/PM₁₀ in above four cities during 2019 were analyzed, and it is helpful to understand the formation and source of haze occurred in the four major polluted areas. PM_2.5/PM₁₀ increasing when PM_2.5 pollution became worse indicates that regional transport is the major pathway for haze. PM_2.5/PM₁₀ decreasing when PM_2.5 pollution became worse indicates that primary emission and secondary chemistry are the major pathways for haze.

How to cite: Xing, C., Liu, C., Liu, H., Li, Q., Tan, W., Lin, H., Ji, X., Zhu, P., Xu, H., and Liu, J.: Observations of aerosol and NO2 vertical profiles derived from MAX-DOAS in four metropolises of China during 2019, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1822, https://doi.org/10.5194/egusphere-egu2020-1822, 2020.

In this study, the spatial-temporal distribution of the NO₂ and SO₂ Vertical Columns Densities (VCDs) in the North China Plain (NCP) region was achieved by the long-distance mobile measurements using the mobile Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) instrument. The mobile observations were taken in both summer (July 2017) and winter (January and February 2018) and the total driving mileage exceeded 3000 km. The concentrations of NO₂ and SO₂ pollution in different seasons and places were significantly different. During winter observations, the serious NO₂ and SO₂ pollution were both observed in northern Anhui province, central Shandong province, and the Beijing-Tianjin-Hebei Region. The evolution and transportation process of the three typical heavy pollution cases were discussed in detail. Combined with the WRF-chem simulated wind field information, the NO₂ transportation flux from the northern Jiangsu province to the northern Anhui province was quantified to be 7.12 kg s^-1. Finally, we estimated the NO₂ and SO₂ emissions from the Dezhou and Hengshui power plants by the plume cross section scanning observation and encircled observation methods, respectively. The NO₂ and SO₂ emission fluxes of the Dezhou power plant are 0.79 and 1.11 kg s^-1, while the NO₂ and SO₂ emission fluxes of the Hengshui power plant are 0.12 and 0.36 kg s^-1. This study has quantitatively analyzed the transportations of atmospheric pollutants and emissions of power plants, which is helpful to understand the occurrence and evolution of pollution and also useful for the government to put forward some policies to protect and control the atmospheric environment.

How to cite: Tan, W., Liu, C., Wang, S., Liu, H., Zhu, Y., Su, W., Hu, Q., and Liu, J.: Long distance mobile MAX-DOAS observation of NO2 and SO2 over the North China Plain, and identification of regional transport and emission of power plant, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1823, https://doi.org/10.5194/egusphere-egu2020-1823, 2020.

Tropopause folds can change the composition of the Upper Troposphere (UT) by bringing down stratospheric parcels with different gas abundances. In this work, partial columns of gases with strong vertical gradients near the tropopause are studied during such events. Partial columns were retrieved from high-resolution infrared spectra measured at subtropical and mid-latitude locations. These stations, contributing to the Network for the Detection of Atmospheric Composition Change (NDACC), are the Altzomoni High-altitude Observatory (19.11°N, 98.66°W) in central Mexico, and the University of Toronto Atmospheric Observatory (43.66°N, 79.40°W) in southern Canada. These datasets constitute a valuable tool for studying the effects of folding on UT composition because of their time resolution (~ 1-hourly, during daylight) and the time periods they span (2012–2019 and 2002–2019, respectively). Our study shows that when tropopause folds occur, partial columns below the tropopause are correlated (anti-correlated) for species whose vertical gradients have the same (different) signs. It is also shown that tropospheric carbon monoxide (CO) in layers closest to the tropopause contributes less to the CO tropospheric partial column during folds because the UT receives low-CO air from the stratosphere.

How to cite: Pavia-Hernandez, R., Grutter, M., Stremme, W., Strong, K., and Yamanouchi, S.: Tropopause folds in North America studied from partial columns of trace gases measured at two ground-based sites, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10924, https://doi.org/10.5194/egusphere-egu2020-10924, 2020.

Abundances of a range of air pollutants can be inferred from satellite UV-Vis spectroscopy measurements by using the unique absorption signatures of gas species. Here, we implemented several spectral fitting methods to retrieve tropospheric NO₂, SO₂, and HCHO from the ozone monitoring instrument (OMI), with radiative simulations providing necessary information on the interactions of scattered solar light within the atmosphere. We analyzed the spatial distribution and temporal trends of satellite-observed air pollutants over eastern China during 2005–2017, especially in heavily polluted regions. We found significant decreasing trends in NO₂ and SO₂ since 2011 over most regions, despite varying temporal features and turning points. In contrast, an overall increasing trend was identified for tropospheric HCHO over these regions in recent years. Furthermore, generalized additive models were implemented to understand the driving forces of air quality trends in China and assess the effectiveness of emission controls. Our results indicated that although meteorological parameters, such as wind, water vapor, solar radiation and temperature, mainly dominated the day-to-day and seasonal fluctuations in air pollutants, anthropogenic emissions played a unique role in the long-term variation in the ambient concentrations of NO₂, SO₂, and HCHO in the past 13 years. Generally, recent declines in NO₂ and SO₂ could be attributed to emission reductions due to effective air quality policies, and the opposite trends in HCHO may urge the need to control anthropogenic volatile organic compound (VOC) emissions.

How to cite: Zhang, C., Liu, C., Hu, Q., Cai, Z., Su, W., Xia, C., Zhu, Y., Wang, S., and Liu, J.: Satellite UV-Vis spectroscopy: implications for air quality trends and their driving forces in China during 2005–2017, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1774, https://doi.org/10.5194/egusphere-egu2020-1774, 2020.

Measurements of the atmospheric total columns (TCs) of trichlorofluoromethane CCl₃F (CFC-11), dichlorodifluoromethane CCl₂F₂ (CFC-12), and chlorodifluoromethane CHClF₂ (HCFC-22)  at the NDACC station St. Petersburg are considered. These gases are the most common representatives of a group of aliphatic organic compounds often called by the DuPont brandname "Freons". Since the 30-ies of the last century, they have been used in industrial applications as refrigerants and propellants. Due to their destructive effect on the ozone layer the production of CFC-11 and CFC-12 has been phased out under the Montreal Protocol entered into force in 1989, which led to the beginning of a decrease in their content. Nevertheless, they are still one of the major anthropogenic sources of active chlorine that destroys ozone in the stratosphere. HCFC-22 became a replacement for the most dangerous for ozone layer freons, but later it was also recognized as a dangerous compound for stratospheric ozone. Nowadays, the production and consumption of HCFC-22 are reduced and it is planned to be completely phased out. Therefore, the monitoring the content of freons in the atmosphere is very important.

Although the content of freons is measured by satellite methods and the sampling method, only the ground-based IR method based on the measurement of IR solar radiation allows obtaining TCs of freons.

A technique for ground-based measurements of the TCs of CFC-11, CFC-12, and HCFH-22 has been developed. The technique is based on the ground-based measurements of solar IR spectra by IFS125HR instrument. For the processing of spectra, the SFIT4 software is used. The analyzed spectral windows are: 1160 – 1162 cm^-1 for CFC-12, 828.75 – 829.4cm^-1 for HCFC-22, and  830 – 860 cm^-1 for CFC-11. Due to the wide spectral interval for CFC-11 retrieval, the preliminary measured spectral transmission function of the instrument filter, the water vapor continuum, and the absorption of radiation by an ice on the MCT detector are taken into account as well. Systematic and random errors of TCs retrieval are estimated as 7.4% and 2.9% for the CFC-11 TCs, 5.0% and 3.7% for the CFC-12 TCs, and 2.0% and 2.7% for the HCFH -22 TCs.

Estimates of TCs above Saint Petersburg have been obtained using the developed technique for the period of 2009 – 2019. The variability during  a day is of 0.8, 0.9, and 3.7 %, the total variabilitiey for 2009 – 2019 is of 3.7, 2.4 and 5.6%, for CFC-11, CFC-12 and HCFC-22, respectively. Trend estimates of CFC-11, CFC-12 and HCFC-22 for 2009 –2019 are –0.31±0.07%, –0.45 ± 0.06% and +2.2 ± 0.14%, respectively, which  are consistent with data from other authors.

In recent years, a tendency toward a decrease of HCFC-22 TCs in the atmosphere above St. Petersburg has been observed, that can be associated with the restriction of HCFC-22 production and use.

Acknowledgements

Measurements of solar radiation were performed with the equipment of the resource center "Geomodel". The investigation was supported by grant 18-05-00426 of the Russian Foundation for Basic Research.

How to cite: Polyakov, A., Makarova, M., Virolainen, Y., Poberovsky, A., and Timofeyev, Y.: Total columns of freons retrieved from ground-based IR solar spectra measurements near Saint Petersburg, Russia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5186, https://doi.org/10.5194/egusphere-egu2020-5186, 2020.

Reactions with hydroxyl radicals and photolysis are the main processes dictating a compound’s residence time in the atmosphere for a majority of trace gases.  In case of very short-lived halocarbons their reaction with OH dictates both the atmospheric lifetime and active halogen release.  Therefore, the accuracy of OH kinetic data is of primary importance for the comprehensive modeling of a compound’s impact on the atmosphere, such as in ozone depletion (i.e., the Ozone Depletion Potential, ODP) and climate change (i.e., the Global Warming Potential, GWP), each of which are dependent on the atmospheric lifetime of the compound.

Atmospheric modeling provides total lifetimes for a number of compounds as well as their partial lifetimes due to specific photochemical removal process (reactions with OH in the troposphere, reactions with OH in the stratosphere, reactions with O(¹D), and UV photolysis), and partial lifetimes associated with the atmospheric removal regions (troposphere and stratosphere).  We have analyzed these results in an effort to find a correlation useful for estimating the lifetimes of other atmospheric trace gases based only on laboratory data of their photochemical properties.  Based on this analysis, we suggest an improved semi-empirical approach for deriving a “best” value of the total atmospheric lifetime due to photochemical removal processes based on laboratory derived photochemical properties of a compound, which is consistent with both empirically derived tropospheric lifetime of Methyl Chloroform and results of rigorous atmospheric modeling.  These aspects will be illustrated in this presentation for a variety of atmospheric trace gases.

The ability to conduct high accuracy laboratory determinations of OH reaction rate constants over the temperature range of atmospheric interest, thereby decreasing the uncertainty of input kinetic data to 2-3% will be demonstrated as well.

How to cite: Orkin, V., Kurylo, M., and Fleming, E.: Atmospheric Lifetimes of Halogenated Hydrocarbons: Laboratory Measurements and Improved Estimations from an Analysis of Modeling Results., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12842, https://doi.org/10.5194/egusphere-egu2020-12842, 2020.

Depletion of the stratospheric ozone layer by chlorine and bromine species has been a major environmental issue since the early 1970s. Following controls on the production of the long-lived halocarbons which transport chlorine and bromine to the stratosphere, the ozone layer is expected to recover over the course of this century. Decreases in the stratospheric loading of chlorine and bromine have been observed and there are signs of this resulting in an increase in ozone in the upper stratosphere and the Antarctic lower stratosphere. However, in contrast to this expectation of increasing stratospheric ozone, Ball et al. (ACP doi:10.5194/acp-18-1379-2018, 2018, ACP doi:10.5194/acp-19-12731-2019, 2019) have reported evidence for an ongoing decline in lower stratospheric ozone at extrapolar latitudes between 60°S and 60°N. Chipperfield et al. (GRL, doi:10.1029/2018GL078071, 2018) analysed these results using the TOMCAT 3-D chemical transport model (CTM). They reported that much of the observed ozone decrease could be explained by dynamical variability. Furthermore, they investigated the potential role for bromine and chlorine from very short-lived species (VSLS) but found only a small contribution.

Very recently, Koenig et al. (PNAS, doi:10.1073/pnas.1916828117, 2020) have reported quantitative observations of almost 1 pptv iodine in the lower stratosphere. They show that this iodine is an important contribution to the local iodine loss budget and speculate that a trend in iodine could therefore explain the observed downward trend in ozone.

Here we use an updated version of the TOMCAT CTM to investigate the impact of iodine on lower stratospheric ozone trends. We repeat the simulations of Chipperfield et al. (2018), using both ERA-Interim and ERA5 reanalyses (to compare the quantification of the dynamical contribution). We use assume trends in the stratospheric injection of iodine to quantify the possible impact of this on global ozone trends through both gas-phase chemistry and novel heterogeneous processes.

How to cite: Chipperfield, M., Feng, W., Dhomse, S., Li, Y., Hossaini, R., and Pfeilsticker, K.: The impact of iodine on ozone trends in the lower stratosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12955, https://doi.org/10.5194/egusphere-egu2020-12955, 2020.

Polychlorinated biphenyls (PCBs) are persistent and hazardous chemicals that are still detected in the atmosphere and other environmental compartments although their production was banned several decades ago. At the Great Lakes region PCBs have been monitored via the IADN network since 1993. In this study, we report results from seven different PCB congeners measured at six different sites around the Great Lakes. The PCBs exhibit a strong seasonal cycle with highest concentrations in summer and lowest concentrations in winter. The concentrations measured in Chicago and Cleveland are higher compared to the concentrations reported from more remote stations. We evaluated the correlations for the seven PCB congeners at each station. PCB-53,-101,-118 and -138 are highly correlated at each of the six stations. PCB-180 is the least correlated with all the other PCBs. This is explicitly true for Eagle Harbor, where PCB-180 and -153 are not correlated with the other 6 PCBs. This may be explained by the less pronounced seasonal cycle of these heavier PCBs at Eagle Harbor. We observed significant correlations between PCB-28 concentrations at the remote stations, but PCB concentrations at the stations of Chicago and Cleveland are only poorly correlated with PCB concentrations at the other stations. The weak correlation of the PCB concentrations measured at the different stations and the relatively high concentrations of the PCB congeners at each station indicate that local conditions and small scale processes (sources, temperature, wind direction, wind speed) dictate the spatial distribution of the  PCBs. We will feed available data on temperature, wind speed, wind direction, emissions, precipitation, ice cover of the Great Lakes and large scale atmospheric teleconnection patterns into a General Additive Model (GAM) to further investigate the relationships between the measured PCB concentrations and selected environmental conditions and atmospheric parameters. 

How to cite: Ubl, S. and Scheringer, M.: Dependencies of Polychlorinated Biphenyl Concentrations Measured at the Great Lakes on Climate Variables, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16640, https://doi.org/10.5194/egusphere-egu2020-16640, 2020.

The Fundamental Data Record for ATMOSpheric Composition (FDR4ATMOS) project is part of the ESA Long Term Data Preservation (LTDP) programme aimed at the preservation and valorization of data assets from ESA’s Earth Observation (EO) Heritage Missions. It has two objectives. The first one is to update the SCIAMACHY processing chain for better Ozone total column data. After the full re-processing of the SCIAMACHY mission with the updated processor versions 9 (Level 1) and version 7 (Level 2), ground-based validation showed that the total Ozone column drifted downward by nearly 2% over the mission lifetime. This drift is likely caused by changes in the degradation correction in the Level 1 processor, that led to subtle changes in the spectral structures. These are misinterpreted as an atmospheric signature. FDR4ATMOS will update the Level 0-1 processor accordingly with the final aim of a mission re-processing.

The main objective of the FDR4ATMOS project is to develop a cross-instrument Level 1 product for GOME-1 and SCIAMACHY for the UV, VIS and NIR spectral range, with focus on the spectral windows used for O3, SO2, NO2 total column retrieval and the determination of cloud properties. Contrary to other projects, FDR4ATMOS does not aim to build harmonised time series based on Level 2 products (geophysical parameters) but to build a Fundamental Data Record (FDR) of Level 1 products, i.e. radiances and reflectances. The GOME-1 and SCIAMACHY instruments together span 17 years of spectrally highly resolved data essential for air quality, climate, ozone trend and UV radiation applications. The goal of the FDR4ATMOS project is to generate harmonised data sets that allow the user to use it directly in long-term trend analysis, independently of the instrument. Since this was never done for highly resolved spectrometers, new methods have to be developed that e.g. take into account the different observation geometries and observation times of the instrument without impacting the spectral structures that are used for the retrieval of the atmospheric species. The resulting algorithms and the processor should also be as generic as possible to be able to easily transfer the methodology to other instruments (e.g. GOME-2 and Sentinel-5p) for a future extension of the time series. The project will support new applications and services and will enhance traceability of satellite-derived data with improved uncertainty estimates based on rigorous metrological principles.

FDR4ATMOS started in October 2019 and is currently in phase 1. We will present the motivation, goals and first results of the project.

How to cite: Lichtenberg, G., Slijkhuis, S., Hamidouche, M., Coldewey-Egbers, M., Aberle, B., Noël, S., Bramstedt, K., Hilbig, T., Bösch, T., Lambert, J.-C., van Gent, J., Hubert, D., Green, P., Hunt, S., Krijger, M., Dehn, A., and Brizzi, G.: The FDR4ATMOS Project, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15059, https://doi.org/10.5194/egusphere-egu2020-15059, 2020.

How to cite: Griffiths, P., Keeble, J., O'Connor, F., Archibald, A., and Pyle, J. and the UKESM1 AerChemMIP team: Atmospheric composition changes in CMIP6 experiments over the North Atlantic region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12154, https://doi.org/10.5194/egusphere-egu2020-12154, 2020.

The hydroxyl radical (OH) is the primary atmospheric oxidant. In this role, OH is involved in the removal of a wide variety of atmospheric pollutants and greenhouse gases. Despite the central role of OH in atmospheric chemistry, important metrics such as interannual variability and trends in OH on large spatial scales remain poorly constrained. This is mainly due to its low abundance and short lifetime of seconds.

Over the past decades, the anthropogenically emitted methyl chloroform (MCF) has been uniquely qualified as a tracer to indirectly constrain OH on large spatio-temporal scales. However, recent box model studies have shown that OH, as estimated from MCF observations, is still very uncertain ^1,2,3. This translates for example to large uncertainties in global methane (CH₄) emissions, even if changes in the global CH₄ burden are well-defined. Box model studies however, do not fully capitalize on the MCF measurement network and the gradients therein. Moreover, they may introduce biases due to incorrect or incomplete representation of atmospheric transport.

Here, we present results from a 4DVAR inversion of MCF over the 1998-2018 period, performed in the 3D chemistry-transport model TM5. Starting from typical OH priors, we find adjustments in the OH spatio-temporal distribution that bring the simulated MCF mole fractions closer to observations. Large uncertainties in this improved estimate remain, but we find that no large interannual variability (>2%) and no significant trend in global mean OH are needed to match MCF observations. We do find significant adjustments in the latitudinal gradients of OH (e.g. an increase in tropical OH).

¹ Rigby, M., et al. PNAS (2017), 114.21: 5373-5377

² Turner, A.J., et al. PNAS (2017), 114.21: 5367-5372

3 Naus, S et al. ACP (2019), 19.1: 407-424

How to cite: Naus, S., Montzka, S., Patra, P., and Krol, M.: Constraints on OH in a global 3D inversion of methyl chloroform, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18458, https://doi.org/10.5194/egusphere-egu2020-18458, 2020.

We present results from the fifteenth annual Greenhouse Gas Bulletin (https://library.wmo.int/doc_num.php?explnum_id=10100) of the World Meteorological Organization (WMO). The results are based on research and observations performed by laboratories contributing to the WMO Global Atmosphere Watch (GAW) Programme (https://community.wmo.int/activity-areas/gaw).

The Bulletin presents results of global analyses of observational data collected according to GAW recommended practices and submitted to the World Data Center for Greenhouse Gases (WDCGG). Bulletins are prepared by the WMO/GAW Scientific Advisory Group for Greenhouse Gases in collaboration with WDCGG.

Observations used for the global analysis are collected at more than 100 marine and terrestrial sites worldwide for CO₂ and CH₄ and at a smaller number of sites for other greenhouse gases. The globally averaged surface mole fractions calculated from this in situ network reached new highs in 2018, with CO₂ at 407.8 ± 0.1 ppm, CH₄ at 1869 ± 2 ppb and N₂O at 331.1 ± 0.1 ppb. These values constitute, respectively, 147%, 259% and 123% of pre-industrial (before 1750) levels. The increase in CO₂ from 2017 to 2018 is very close to that observed from 2016 to 2017 and practically equal to the average growth rate over the last decade. The increase of CH₄ from 2017 to 2018 was higher than both that observed from 2016 to 2017 and the average growth rate over the last decade. The increase of N₂O from 2017 to 2018 was also higher than that observed from 2016 to 2017 and the average growth rate over the past 10 years. The National Oceanic and Atmospheric Administration (NOAA) Annual Greenhouse Gas Index (AGGI) shows that from 1990 to 2018, radiative forcing by long-lived greenhouse gases (GHGs) increased by 43%, with CO₂ accounting for about 81% of this increase.

The Bulletin highlights the value of the long-term measurement of the GHGs isotopic composition. In particular, it presents the use of the radiocarbon and ¹³C measurements in atmospheric CO₂ in discriminating between fossil fuel combustion and natural sources of CO₂. The simultaneous decline in both ¹³C and ¹⁴C content alongside CO₂ increases can only be explained by the ongoing release of CO₂ from fossil fuel burning. The Bulletin also articulates how the measurements of the stable isotopes can be used to provide the insights into the renewed growth of methane that started in 2007. Though there are several hypotheses articulated in the peer-reviewed literature, the most plausible is that an increase has occurred in some or all sources of biogenic (wetlands, ruminants or waste) emissions, which contain relatively little ¹³C. An increase in the proportion of global emissions from microbial sources may have driven both the increase in the methane burden and the shift in δ¹³C-CH₄.

How to cite: Tarasova, O., Vermeulen, A., Turnbull, J., Sawa, Y., and Dlugokencky, E.: The state of greenhouse gases in the atmosphere using global observations through 2018, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7651, https://doi.org/10.5194/egusphere-egu2020-7651, 2020.

The Arctic region is one of the main areas of greenhouse gases sources due to large amount of biomass, carbon stocks in the soil and extensive wetlands. Large resources of previously inactive organic carbon may take part in atmospheric chemical reactions under melting permafrost conditions. In this case, carbon dioxide concentrations will increase in the atmosphere. Since 2015 Arctic and Antarctic Research Institute in cooperation with Finnish Meteorological Institute have been measuring the continuous concentrations of water vapor, methane, carbon dioxide and carbon monoxide at Research Station "Ice Base Cape Baranova" (79° 18´ N, 101° 48´ E, 30 m asl.) using cavity ringdown spectroscopy (CRDS) analyzer Picarro G2401. The sampling inlet is located at 10 m height.

Data preprocessing consists of deleting values obtained during power failures and 2 minutes after calibration. The values for wind directions corresponding to the transfer from diesel power station (90 - 145 °) and for wind speeds less than 3 m/s were also discarded because in this case polluted air may be distributed over the station homogeneously. After that data were adjusted taking into account the nearest calibration values by linear interpolation. The archive of carbon dioxide concentrations data averaged over each hour from October 2015 to December 2019 was used for further analysis.

CO₂ time series are characterized by a pronounced annual variation with concentration decreasing in summer months. The absorption by sea phytoplankton in the absence of sea ice cover causes the annual variability of carbon dioxide. Besides, the predominant presence of stable stratification of the atmospheric surface layer throughout the polar night contributes to accumulation of the gas in the surface layer in winter. The annual amplitude is 18–20 ppm approximately, which is consistent with the data of Alert and Barrow polar stations.

The analysis of the dependence of registered concentration distribution on the wind direction shows that the highest values are observed during the air-mass transfer from the south-western and northern directions. If the first case can be explained by the anthropogenic impact and presence of extensive wetlands in the summer, the reason for the second one requires a more detailed analysis. Applying the HYSPLIT trajectory model for cases of elevated values of greenhouse gas concentrations did not allow us to obtain an unambiguous answer. Although elevated values were observed, as a rule, when air masses transferred from the regions of Norilsk, Yamal, the Kola Peninsula, and Lena estuary, however, there were cases of elevated concentrations during the transfer of air masses from the Arctic Ocean. This may be due to the action of any local sources, but their detection requires additional data analysis. The work had been executed in frame of CNTP Roshydromet 1.5.3.3.

How to cite: Loskutova, M., Makshtas, A., Laurila, T., and Asmi, E.: Carbon dioxide variability at Research Station "Ice Base Cape Baranova" during 2015 - 2019, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20807, https://doi.org/10.5194/egusphere-egu2020-20807, 2020.

The Mediterranean basin is considered a global hot-spot region for climate change and air-quality. CO₂ is the single most-important anthropogenic greenhouse gas (GHG) in the atmosphere, accounting approximatively for ∼63% of the anthropogenic radiative forcing by long-lived GHG. According to Le Quérée et al. (2018), the increasing of the atmospheric CO₂ mixing ratios in the global atmosphere is driven by fossil fuel and cement production.
In order to reduce GHG emissions and taking into account the needs for economy and society development, schemes of regulation and emission trading have been adopted at international, national, and city levels. The implementation of these regulation, to achieve the goal successfully, needs scientific evidence and information provided on consistent datasets. In the last year, efforts are dedicated to set up harmonized reference networks at difference scales (WMO/GAW, AGAGE, ICOS).
In this work, we analysed a set of continuous long-term measurements of CO₂ carried out at 4 atmospheric observatories in Italy belonging to the WMO/GAW network and spanning from the Alpine region to central Mediterranean Sea: Plateau Rosa (western Italian Alps, 3480 m a.s.l.), Mt. Cimone (northern Apennines, 2165 m a.s.l.), Capo Granitola (southern Sicily coastline) and Lampedusa Island. Mt. Cimone is also a “class-2” ICOS station, while Plateau Rosa and Lampedusa are in the labelling process. Starting time of GHG observations range from 1979 for Mt. Cimone to 2015 for Capo Granitola. Due to their different locations and ecosystems, they provide useful hints to investigate CO₂ variability on different latitudinal and altitudinal ranges in the Mediterranean basin and to study of natural and anthropogenic-related processes able to affect the observed variability.
The study addresses primarily differences in daily and seasonal cycles at the different sites, and implemented a procedure to identify background conditions called BaDSfit (Background Data Selection for Italian stations; Trisolino et al., submitted). This methodology was originally used at Plateau Rosa station (Apadula, 2019) and it is based on the Mauna Loa data selection method (Tans and Thoning, 2008). BaDSfit consist of three steps and an optimization of the procedure was carried out with a sensitivity study.  Marked differences among the daily cycles at the various sites exist. The effect of the data selection on the seasonal and diurnal cycle and long-term evolution is investigated. The BaDSfit lead to a more coherent diurnal and seasonal evolution of the different datasets, is able to identify background condition and allows the separation of local/regional scale from large scale phenomena in the CO₂ time series.

How to cite: Trisolino, P., di Sarra, A., Sferlazzo, D., Piacentino, S., Monteleone, F., Di Iorio, T., Apadula, F., Heltai, D., Lanza, A., Vocino, A., Caracciolo di Torchiarolo, L., Bonasoni, P., Calzolari, F., Busetto, M., and Cristofanelli, P.: Italian network of four permanent observatories: implementation of background data selection (BaDSfit) and 5-year analysis of the atmospheric CO2 mixing ratio., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9432, https://doi.org/10.5194/egusphere-egu2020-9432, 2020.

Within the framework of the research infrastructure IAGOS (In-service Aircraft for a Global Observing System), a cavity ring-down spectroscopy (CRDS)-based measurement system for the autonomous measurement of the greenhouse gases (GHGs) CO₂ and CH₂, as well as CO and water vapour is deployed on a Lufthansa Airbus A330 since September 2018. This IAGOS-CORE system is equipped with a two-standard in-flight calibration system, allowing for trace gas measurements to be fully traceable to WMO calibration scales. Various lessons have been learned during the first deployment periods related to the autonomous operation of the system over periods of several months, enabling the future extension of the GHG measurements to aircraft from further airlines. Apart from the presentation of the observations, the presentation will discuss the data quality and uncertainty estimation.

A further CRDS system for autonomous measurement CO₂ and CH₄ is integrated within the instrumented IAGOS-CARIBIC container deployed on board an Airbus A340 on a bi-monthly schedule since July 2018. By now this system has provided data from more than 30 flights. Data will be presented, and the potential of the observations for research applications will be introduced. Also the availability of IAGOS GHG data to the research community will be discussed.

How to cite: Gerbig, C., Franke, H., Stosius, R., Obersteiner, F., Gehrlein, T., and Zahn, A.: Update on IAGOS greenhouse gas observations from commercial airliners, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16371, https://doi.org/10.5194/egusphere-egu2020-16371, 2020.

Continuous measurements of long-lived greenhouse gases at ground-based monitoring stations are frequently influenced by regional surface fluxes and atmospheric transport processes, which induce variability at a range of timescales.  Dissecting this variability is critical to identifying long-term trends and understanding regional source-sink patterns, but it requires a robust characterization of the underlying signal comprising the background air composition at a given site.  Methods of background signal extraction that make use of chemical markers or meteorological filters yield reliable estimates, but often must be adapted for site-specific measurement conditions and data availability.  Statistical baseline extraction tools provide a more generally transferable alternative to such methods.  Here, we apply one such technique (REBS) to a continuous time series of atmospheric CO₂ readings at Mace Head, Ireland and compare the results to a modeled baseline signal obtained from local wind observations. We then assess REBS’ performance at two continental sites within the Integrated Carbon Observation System (ICOS) network at which baseline signals are derived using back-trajectory analyses.  Overall, we find that REBS effectively reduces the bias in wintertime baseline estimation relative to other statistical techniques, and thus represents a computationally inexpensive and transferable approach to baseline extraction in atmospheric time series. To investigate one potential application of such an approach, we examine wintertime synoptic-scale CO₂ excursions from the REBS baseline during the period 2015-2019.  Our goal is to identify relationships between the timing and strength of such events and to better understand sub-seasonal variability in CO₂ transport over Europe.

How to cite: Resovsky, A., Ramonet, M., Rivier, L., Conil, S., and Spain, G.: Using robust baseline extraction to examine synoptic-scale variability in European CO2, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18864, https://doi.org/10.5194/egusphere-egu2020-18864, 2020.

The challenge in quantifying the sources and sinks of atmospheric carbon dioxide (CO₂) is that the CO₂ taken up by plants during photosynthesis cannot be distinguished from the CO₂ released by plants and micro-organisms during respiration. It has been shown that carbonyl sulfide (OCS), the sulphur-containing analogue of CO₂, can be used as a proxy for photosynthesis. The relationship between the vegetative flux of OCS and CO₂ has been quantified for various species of plants and ecosystems, the results of which have been used in observing the relationship on a continental scale. The aim of this project is to both quantify the location and magnitude of the sources and sinks of atmospheric OCS, and to use these data to infer photosynthetic uptake of CO₂ by vegetation on a global scale.

A tracer version of the 3-dimensional chemical transport model TOMCAT has been adapted to include eleven different sources and sinks of OCS, including direct and indirect oceanic emissions, vegetative uptake and stratospheric photolysis. The modelled OCS (TOMCAT-OCS) distribution between 2004 and 2018 has been co-located spatially and temporally to OCS profiles measured by the Atmospheric Chemistry Experiment (ACE-FTS) over the 5 – 30 km altitude, showing generally good agreement. Furthermore, surface TOMCAT-OCS has been compared to OCS measurements made at twelve NOAA-ESRL sites, across both hemispheres, showing that the model captures the seasonal cycle at the surface.

There have been several calls in recent years for a new satellite product of atmospheric OCS, which this project aims to satisfy. Work is ongoing to retrieve OCS total columns from measurements taken by the Infrared Atmospheric Sounding Interferometer (IASI) instruments on-board the MetOp satellites. The University of Leicester IASI Retrieval Scheme (ULIRS) has been adapted to retrieve OCS columns globally. Various case studies for different geographic regions and time periods will be presented and compared to other satellite observations.

How to cite: Cartwright, M. P., Harrison, J. J., Moore, D. P., Remedios, J. J., Chipperfield, M. P., and Pope, R. J.: Investigation of global atmospheric carbonyl sulphide between 2004 and 2018: an observational and modelling study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18289, https://doi.org/10.5194/egusphere-egu2020-18289, 2020.

Methane (CH₄) is the second most important anthropogenic greenhouse gas. Its Global Warming Potential over 100 years (GWP₁₀₀) exceeds 28 times that of CO₂. Methane surface concentrations have steadily increased since the pre-industrial due to industrialisation combined with fossil fuel use. In 1850, around the onset of heavy industrialisation in Europe and North America, the CH₄ mole fraction was approximately 700 ppbv, and since then it has increased 2.5-fold to slightly more than 1830 ppbv in 2015. Fossil fuel use, raising of livestock, and cultivation of rice are the dominant contributions to the atmospheric methane burden at present with significant emissions from natural wetlands also playing a central role.

Here we present first results from the UK Earth System Model (UKESM1.0). The default release version of UKESM1.0 has been extended to represent the methane cycle fully interactively, including dynamic wetlands with global CH₄, full stratospheric-tropospheric CH₄ chemistry, and CH₄ surface deposition. The extended configuration is capable of simulating the climate feedbacks on methane wetland emissions which are typically neglected in current Earth system models. Our simulation is driven with anthropogenic CH₄ emissions from CMIP6. We conducted fully-coupled transient simulations of the atmospheric CH₄ burden from 1850 to 2100 based on the historic and two future scenarios (SSP3-7.0 and SSP1-2.6) scenarios.

We compare the time series of global CH₄ surface concentrations between the default CH₄ concentration-driven configuration of UKESM1.0 with the fully-interactive emissions-driven configuration. Surface concentrations for the emissions-driven simulation show reasonable agreement with the concentration-driven simulation, but a low bias in the fully interactive simulation gradually emerges after about 1920 which reaches approximately -250 ppbv in the 2000s. We then present a full-cycle CH₄ budget analysis based on decadal means for every 50 years between 1850 and 2100. We demonstrate that methane burden and surface mole fractions are expected to return to their 1930s values under SSP1-2.6, albeit with the natural methane sources still heavily disturbed from their original state. We also produce a detailed analysis of the contribution of wetland CH₄ emissions for the 250 years of simulation.

How to cite: Folberth, G. A., Gedney, N., Jones, C. D., O'Connor, F. M., Sellar, A. A., and Wiltshire, A.: Methane Past, Present and Future -- 250-year Methane Trend from a Fully Interactive Earth System Model Simulation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12808, https://doi.org/10.5194/egusphere-egu2020-12808, 2020.

Measurements of stable isotope ratios of atmospheric CH₄ (δ¹³C-CH₄, δD-CH₄) have been utilized to evaluate contributions of individual CH₄ sources and sinks to global atmospheric CH₄ budget. However, given the uncertainty of both the source isotope signatures and kinetic isotope effects, recent estimates of the global atmospheric CH₄ budget using stable isotope observations are still inconclusive. Radiocarbon measurements (Δ¹⁴C-CH₄) could provide stronger additional constraint on the fossil-fuel CH₄ sources (i.e.,¹⁴C-free), but the uncertainty of ¹⁴CH₄ emissions from nuclear power facilities and a lack of data have limited such utilization. Here we describe a new approach to estimate plausible global CH₄ emissions and sinks scenarios over 1850–2015 using observations and one-box model simulations of atmospheric CH₄, δ¹³C-CH₄, δD-CH₄, and Δ¹⁴C-CH₄. As inputs to the model, we prepare a priori bottom-up CH₄ emission inventories, total atmospheric CH₄ lifetime, source and sink isotope signatures, nuclear power facility database, and atmospheric δ¹³C-CO₂ and Δ¹⁴C-CO₂ observations and their uncertainties. We then run a Monte Carlo simulation of atmospheric CH₄, δ¹³C-CH₄, δD-CH₄, and Δ¹⁴C-CH₄ over the period using the inputs with the uncertainties. By using the observational CH₄ and three isotope constraints, we derive the best combinations of biogenic, anthropogenic fossil-fuel, natural geologic, biomass-burning, and nuclear power facility emissions and total CH₄ lifetime. We find that reconciling CH₄, δ¹³C-CH₄, δD-CH₄, and Δ¹⁴C-CH₄ observations indicates that (1) natural geologic emissions are likely smaller than the recent bottom-up estimate 43–50 Tg CH₄ yr^-1 reported by Etiope et al. (2019), (2) biomass burning and anthropogenic fossil emissions are larger than current bottom-up estimates, and (3) biogenic emissions are somewhat smaller than current bottom-up estimates. Our finding suggests multiple isotope measurements, including Δ¹⁴C-CH₄, have a strong potential to evaluate the current and future bottom-up global CH₄ emission inventories.

How to cite: Fujita, R. and Graven, H.: Impact of atmospheric radiocarbon and stable isotope measurements on understanding the global CH4 budget over 1850–2015, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9635, https://doi.org/10.5194/egusphere-egu2020-9635, 2020.

CFC-11 is a potent ozone depleting gas and is regulated under the Montreal Protocol. The rate of decline in global CFC-11 concentrations has slowed since 2013 largely due to the renewed, increasing emissions from eastern China (Montzka et al, Nature, 2018; Rigby et al, Nature, 2019). However, regional inversions suggest that this increase only accounts for 40-60% of the global rise. Therefore, there is an urgent need for emission estimates in other regions or countries. A global 3D inversion of atmospheric measurements is essential to improve our understanding of CFC-11 emission trends and sources, but it requires a reliable emission inventory as a prior estimate. In this study, we develop a gridded bottom-up inventory of global CFC-11 emissions from 2008 to 2019. Our inventory is driven by various, gridded proxy datasets including population, energy consumption, GDP per capita, and industrial clusters. A machine learning model is built between the proxy data and the previous emission estimates for eastern China, Korea, and Japan derived from inversions of AGAGE and NOAA surface measurements (Rigby et al, Nature, 2019). Our model is cross-validated in the East Asia and then applied to the other regions and countries to construct the gridded inventory with error characterization. Use of our inventory as prior information in future inverse analyses can help better quantify spatial distributions and sources of CFC-11 emissions as well as better guide the regulation of CFC-11.

How to cite: Sheng, J. and Prinn, R.: A gridded inventory for global CFC-11 emissions from 2008 to 2019, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3139, https://doi.org/10.5194/egusphere-egu2020-3139, 2020.

Since 2004, the Atmospheric Chemistry Experiment – Fourier Transform Spectrometer (ACE-FTS) instrument has been measuring concentrations of chlorofluorocarbons (CFCs) in the stratosphere and upper troposphere and is currently the only satellite instrument that measures vertically resolved profiles of CFC‑11. Since CFCs are major ozone depleting substances, monitoring their atmospheric abundances is critical for understanding ozone layer recovery. Recent studies based solely on surface-level measurements have shown strong evidence for new CFC‑11 production, leading to an increase in CFC‑11 emissions over the past decade. In this study, the TOMCAT/SLIMCAT 3-D chemical transport model is used in order to bridge the altitude/geolocation gap between ACE-FTS measurements in the UTLS and surface level measurements. Trends in two different time periods over the ACE-FTS mission, 2004-2012 and 2013-2018, are examined to determine if the recent change in surface level CFC-11 trends is influencing UTLS concentrations. The ACE-FTS measurements show that, below ~10 km, the rate of decrease of global CFC-11 concentrations was slower during 2013-2018 (-1.2 pptv/year) than during 2004-2012 (‑2.0 pptv/year). Similar trends are observed in the model data for the same spatial/temporal regions.

How to cite: Sheese, P., Walker, K., Boone, C., Saunders, L., Dhomse, S., Feng, W., and Chipperfield, M.: A recent slowdown in the decline of CFC-11 concentrations in the upper troposphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11308, https://doi.org/10.5194/egusphere-egu2020-11308, 2020.

Water vapour in the upper troposphere and lower stratosphere (UTLS) has a significant impact both on the radiative and chemical properties of the atmosphere. Reliable water vapour observations are essential for the evaluation of the accuracy of UTLS water vapour from model simulations, and thereafter of the contribution to the global radiative forcing and climate change. Limb-viewing and nadir satellites provide high quality water vapour observations above the lower stratosphere and below the upper troposphere, respectively, but show large uncertainties in the tropopause region.  Within the ESA Water Vapour Climate Change Initiative, we have developed a new scheme to optimally estimate water vapour profiles in the UTLS and in particular across the tropopause, by merging observations from a set of limb and nadir satellites from 2010 to 2014. The new data record of vertically resolved water vapour is validated against the aircraft in-situ water vapour observations from the JULIA database and frostpoint hydrometer records from WAVAS. Furthermore, the new data record is used to evaluate the UTLS water vapour distribution and interannual variations from chemistry-climate model (CCM) simulations and the ERA-5 reanalysis.

How to cite: Ye, H., Hegglin, M., Krämer, M., Rolf, C., Laeng, A., Hurst, D., and Vömel, H.: Water vapour in the Upper Troposphere and Lower Stratosphere (UTLS): A new vertically resolved dataset from limb and nadir satellite observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18925, https://doi.org/10.5194/egusphere-egu2020-18925, 2020.