AS3.9

Introduction

The Arctic region is particularly sensitive to global climate change, experiencing warming at twice the rate of the global average. Changes within and outside of the Arctic (e.g., meteorology, atmospheric transport, and precipitation patterns) can have consequences for the sources and sinks of aerosols. Atmospheric aerosols can alter the planetary radiation balance directly through scattering and absorption and indirectly through modification of cloud properties. Understanding the direction and magnitude of recent changes in the Arctic aerosol population is key to elucidating the implications for the changing Arctic, although this remains a scientific challenge. Here we report a Pan-Arctic view of recent trends for aerosol particle number concentrations in different size fractions.

Measurement Site & Methods

Measurements were obtained from different stations around the Arctic including Villum Research Station (Villum, 81^°36’ N, 16^°39’ W, 24 m a.s.l) in northeastern Greenland, Alert (81°28’ N, 62°30’ W, 210 m a.s.l.) in the Canadian Archipelago, Zeppelin Observatory (78°56’ N, 11°53’ E, 474 m a.s.l.) on Svalbard, Pallas (67°58’N, 24°07’ E, 560 m a.s.l.) in northern Finland, and Tiksi (71°36’ N, 128°53’E, 1 m a.s.l.) in the Siberian Arctic.

Particle number size distributions (PNSD) were measured using a Scanning Mobility Particle Sizer (SMPS) at Villum and Alert, and a Differential Mobility Particle Sizer (DMPS) at Zeppelin, Pallas, and Tiksi. Measurements were collected from 2010 to 2018 at all sites except for Zeppelin (2011 to 2019). Number concentrations were calculated by integrating the PNSD for three size fractions: Nucleation (10-35 nm), Aitken (35-80 nm), and Accumulation (80-300 nm). Nucleation number concentrations were unavailable for Zeppelin.

The trends in the number concentration for these size fractions were identified and quantified using the Mann-Kendal test and Theil Sen slope on the 90^th % confidence interval via the 3PW algorithm, using the daily median as temporal aggregation and meteorological seasons as temporal segmentation. Only statistically significant trends are discussed.

Results

Although the sites Villum, Alert, and Zeppelin are all located in the High Arctic (> 75° N) and relatively close to one another, there are differences between the direction and magnitude of trends for the size fractions. For example, at Villum, increasing trends are observed for the Nucleation fraction during spring and summer. Interestingly, at Alert, decreasing trends are observed for the Accumulation fraction during spring and autumn. At Zeppelin, no significant trends were observed for any fraction during any season.

           Similar to the High Arctic sites, for the continental sites, Tiksi and Pallas, no uniform picture for the direction and magnitude of trends in the size fractions is observed. At Tiksi, decreasing trends for both the Aitken and Accumulation fractions are detected during summer and autumn. While at Pallas, no significant trends were observed during any season.

           This work offers insight into the climatic implications (i.e., radiative balance and cloud properties) for a future Arctic climate by monitoring changes of aerosol concentrations in optically and cloud-relevant sizes. Future work will investigate the causes of these trends.

How to cite: Pernov, J. B., Tunved, P., Sharma, S., Asmi, E., Kivekäs, N., Schmale, J., Ström, J., Hansson, H.-C., Skov, H., and Massling, A.: Pan-Arctic trends of aerosol particle number concentrations in different size fractions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6026, https://doi.org/10.5194/egusphere-egu22-6026, 2022.

Modern-Era Retrospective analysis for Research and Applications (MERRA-2) generated  PM_2.5  concentrations are widely used to understand the spatio-temporal variability of PM_2.5 across the globe. Only PM_2.5 data from black carbon, organic carbon, sulphate, sea-salt, and dust are provided by MERRA-2. However, previous studies validated MERRA-2 PM_2.5 concentrations obtained by combining all five species data against in-situ ​total PM_2.5 concentrations. To the best of our knowledge, this is the first study over India to validate MERRA-2 species wise PM2.5 concentrations utilizing in-situ surface measurements made over a site at Bhopal (23.285° N, 22.277° E). Bhopal is one of the eleven COALESCE (Carbonaceous Aerosol Emissions, Source Apportionment and Climate Impacts) network regionally representative sites in India. 24 hour integrated filter-based samples (N = 165) collected during 2019, using the MetOne SASS® speciation sampler were used to measure mass and aerosol species concentrations by a variety of analyses. Our results show that the MERRA-2 well captures the aerosol species data at Bhopal. However, MERRA-2 underestimated the annual mean in-situ concentration of organic carbon, black carbon, and sulphate by 1.9 µg m ^-3 (~22 %), 1.3 µg m ^-3 (~47 %) and 0.9 µg m ^-3 (~11 %), respectively and overestimated the sea salt and dust components by 0.75 µg m ^-3 (~95 %) and 8.5 µg m ^-3 (~153 %), respectively.  It is pertinent to note that dust from surface aerosol chemical species measurements was re-constructed using elemental aluminium, silicon, potassium, calcium, titanium, manganese concentrations. Further, the annual mean MERRA-2 PM_2.5 mass (reconstructed from its constituent species) underestimated the average in-situ PM_2.5 mass by 13.55 µg m ^-3 (~26.16 %). This underestimation is likely due to aerosol nitrate not being included in the MERRA2 PM_2.5 mass and uncertainties in aerosol species concentrations resulting from limitations in the chemical transport model set-up and emissions inventories. This study discusses the possible causes of disagreements between in-situ measurements and MERRA2 products, in addition to estimating the effect of including nitrate in the MERRA2 PM_2.5 mass reconstruction.

How to cite: Devaliya, S., Maheshwarkar, P., Bhardwaj, A., Haswani, D., Shukla, D., and Sunder Raman, R.: Evaluation of the MERRA-2 PM2.5 mass and its constituent chemical species concentrations over a COALESCE network site in Bhopal, India, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-537, https://doi.org/10.5194/egusphere-egu22-537, 2022.

Studying the changes of PM_2.5 and PM₁₀ in the Yangtze River Economic Belt will help promote the comprehensive management of regional air pollution and promote the ecological environment protection and high-quality economic development of the Yangtze River Economic Belt. This paper selects monthly observation data of six pollutants from 126 cities in the Yangtze River Economic Belt from 2015 to 2020, and applies Mann-Kendall mutation test, Pearson correlation coefficient analysis, spatial autocorrelation analysis and spatial regression analysis to study PM_2.5 and PM₁₀ temporal and spatial distribution, evolution characteristic and driving factors, and applies the HYSPLIT backward trajectory analysis model to study the potential impact of long-distance air transport and atmospheric boundary layer conditions on the diffusion and transmission of PM_2.5 and PM₁₀ pollution sources in the Yangtze River Economic Belt. The annual average concentrations of PM_2.5 and PM₁₀ in the Yangtze River Economic Belt significantly decreased year by year, with obvious seasonal trend of high concentration in winter and low concentration in summer. There is a significant positive spatial correlation relationship, and the spatial accumulation is obvious. In addition, there is a significant positive correlation and homology with other gaseous pollutants. The air mass retrospective direction and atmospheric boundary layer conditions of the upper, middle and lower Yangtze River urban agglomerations have different effects on PM_2.5 and PM₁₀. The regional GDP, the proportion of the secondary industry, the population density and the green coverage rate in the built-up areas all affected positively the local PM_2.5 and PM₁₀ concentrations. Overall, regional cooperating depollution, synergetic reduction of various air pollutants and transformation of economic development patterns can fundamentally solve the problems of PM_2.5 and PM₁₀ pollution in the Yangtze River Economic Belt.

How to cite: Yao, Y. and He, Z. Q.: Variation Characteristics of PM2.5 and PM10 Concentration and its Driving Factors in the Yangtze River Economic Belt, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6890, https://doi.org/10.5194/egusphere-egu22-6890, 2022.

The Stratospheric Aerosol and Gas Experiment III (SAGE III) instrument installed on the International Space Station (ISS) has completed almost half of a decade of data collection and production of science data products. The SAGE III/ISS is a solar and lunar occultation instrument that scans the light from the Sun and Moon through the limb of the Earth’s atmosphere to produce vertical profiles of aerosol, ozone, water vapor, and other trace gases. It continues the legacy of previous SAGE instruments dating back to the 1970s to provide data continuity of stratospheric constituents critical for assessing trends in the ozone layer. This presentation shows how SAGE III/ISS aerosol and gas vertical profiles continue to benefit a worldwide database of in situ and satellite data for climate observation.

How to cite: Kizer, S., Roell, M., Flittner, D., Damadeo, R., Leavor, K., Roller, C., Hurst, D., Hall, E., Jordan, A., Cullis, P., Johnson, B., and Querel, R.: Stratospheric Aerosol and Gas Experiment III on the International Space Station(SAGE III/ISS): Continuing the Legacy of SAGE Data Products, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13523, https://doi.org/10.5194/egusphere-egu22-13523, 2022.

COVID-19 required governments across the globe put into place a range of measures which resulted in many industries suspending operations and most citizens (i.e., non ‘key-workers’) staying in their homes. As such, anthropogenic activity around the globe decreased rapidly, to such an extent that emissions of air pollutants began to decline dramatically, with this period now being referred to as an ‘anthropause’. In the early stages of the pandemic, remote sensing data from satellites indicated that nitrogen dioxide (NO₂) concentrations had fallen by as much as 30% across China and by as much as 50% across areas of central Europe. Early work using in-situ measurements confirmed these findings, with studies from China, Korea, India, the USA and Europe all reporting decreases in ambient NOx concentrations. The UK government advised that the general population should avoid ‘non-essential’ travel and social contact, on 16th March 2020.  Subsequently, on 23rd March 2020, the government announced a UK-wide partial ‘lockdown’, to contain the spread of the virus. 

In this work, we combine findings from the University of Brighton’s Brighton Atmospheric Observatory and the ESA's Sentinel-5P satellite, to investigate changes in tropospheric Nitrogen Dioxide concentrations in the South East of the UK during the COVID-19 pandemic. BAO comprises a climate controlled, clean laboratory and analytical instruments for making detailed, real-time measurements of tropospheric composition, and is situated in a suburban background environment, roughly 5 km from Brighton city centre. 

Maps showing regional daily average NO₂ concentrations as recorded by TROPOMI were created over (a) the period 25/03/2019–22/04/2019 (i.e. the pre-pandemic baseline) and (b) 23/03/2020–20/04/2020 (i.e. post-implementation of lockdown restrictions). TROPOMI measurements were compared to measurements made on the ground using a long-path DOAS (total path length 300m) for the same time periods. The data confirms findings from analysis of in-situ monitor observations made by the Sussex-Air Network and DEFRA Automatic Urban and Rural Network (AURN), extending the reach of the data capture to the entire South East of the UK on a 7 × 7 km resolution scale. In-line with the in-situ monitors, TROPOMI measured a decrease in the concentrations of NO2 across the entire region during the lockdown, with the regional average value falling by 33%, from 4.9 × 10^16 to 3.3 × 10^16 molec m^-2. The largest changes in NO2 were observed in the centre of the region, in the areas surrounding London and at certain coastal locations.  

TROPOMI measured NO2 values across Brighton and Hove during the 2020 lockdown period to be 59% of those measured over roughly the same time period the previous year (with mean values falling from 4.4 × 10^16 to 2.9 × 10^16 molecule m^-2), comparing favourably with DOAS, which recorded NO₂ values that were ~64% of those measured during the previous two years over roughly the same time period.  

The methodology is also extended to London, Birmingham and Manchester, the 1st, 2nd and 6th largest cities within the UK. 

How to cite: Gregg, D., Wyche, K., Nichols, M., Parfitt, H., Beckett, P., Smallbone, K., and Monks, P.: Changes in ambient air quality and atmospheric composition and reactivity in the South East of the UK as a result of the COVID-19 lockdown, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2760, https://doi.org/10.5194/egusphere-egu22-2760, 2022.

Changes in the atmospheric composition in different periods of 2020 in Moscow, associated with the COVID-19 pandemic preventing measures of varying intensity and with corresponding reduction in emissions of pollutants, were investigated. Surface concentrations of nitrogen dioxide NO₂, carbon monoxide CO, ozone O₃, aerosol fraction PM₁₀ and meteorological parameters in different periods of 2020 are compared with similar data for the previous 5 years. The analysis of ground-based measurements, as well as high-resolution satellite distributions of CO and NO₂, indicated that the content of major pollutants and its spatial distribution in the Moscow region were significantly affected by both restrictive measures and abnormal meteorological conditions in 2020. It is possible to obtain quantitative estimates of the contribution of both factors using transport and chemical modeling based on detailed inventory of anthropogenic emissions.

Additionally, some characteristics of atmospheric composition long-term trends in Moscow region are analyzed and discussed.

The study was supported by Russian Science Foundation under grant №21-17-00210.

How to cite: Kirillova, N., Skorokhod, A., Rakitin, V., and Fedorova, E.: The impact of COVID-19 pandemic preventing measures and meteorological conditions on the atmospheric air composition in Moscow in 2020, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4755, https://doi.org/10.5194/egusphere-egu22-4755, 2022.

We present air quality and trace gas observations at the regional Global Atmosphere Watch (GAW) station Pha Din (PDI) in rural Northwestern Vietnam. PDI is located in a sparsely populated area on the top of a hill (1466 m a.s.l.) [1], and frequently receives pollution plumes from large-scale fires on the Indochinese Peninsula [1]. We previously analyzed carbonaceous PM_2.5 chemical composition in an intensive campaign conducted during 3 weeks in March-April 2015. The study included measurements of elemental and organic carbon (EC/OC) and more than 50 organic markers, such as sugars, PAHs, fatty acids and nitro-aromatics [2]. For this intensive campaign, we linked trace gas mixing ratios of CO, CO₂, CH₄ and O₃ to a statistical classification of large-scale fires, which was based on organic aerosol composition. We found increased CO and O₃ levels during medium and high biomass burning influence during March-April 2015. A backward trajectory analysis confirmed different source regions for the identified periods based on the organic aerosol cluster. The more polluted periods were characterized by trajectories from southwest, with more continental recirculation of the medium cluster, and more westerly advection for the high cluster. Cleaner air masses instead arrived from northeast, i.e., mainland China and Yellow sea during this period.  These findings highlighted that biomass burning in Northern Southeast Asia significantly enhances the regional organic aerosol loading, chemical PM_2.5 composition and the trace gases in northwestern Vietnam [2]. For our contribution to EGU22, we extend this analysis to a multi-year period and present continuous trace gas observations of CO₂, CH₄, CO, and O₃ conducted at PDI since 2014. The data are interpreted with atmospheric transport simulations, and add valuable insight on air quality and trace gas mixing ratios in a region of scarce data availability.

REFERENCES: [1] Bukowiecki, N. et al. Effect of Large-scale Biomass Burning on Aerosol Optical Properties at the GAW Regional Station Pha Din, Vietnam. AAQR 19, 1172–1187 (2019). [2] Nguyen, D. L, et al. Carbonaceous aerosol composition in air masses influenced by large-scale biomass burning: a case-study in Northwestern Vietnam. Atmos. Chem. Phys., 21, 8293–8312 (2021) https://doi.org/10.5194/acp-21-8293-2021

FUNDING AND ACKNOWLEDGMENTS:  Capacity Building and Twinning for Climate Observing Systems (CATCOS), GAW Quality Assurance/Science Activity Centre Switzerland (QA/SAC-CH), Swiss National Science Foundation (SNSF) (194390), German Academic Exchange Service (DAAD), Vietnam Academy of Science and Technology (VAST).

How to cite: Pieber, S. M., Nguyen, D.-L., Czech, H., Henne, S., Bukowiecki, N., Nguyen, N. A., Buchmann, B., Emmenegger, L., and Steinbacher, M.: Air quality and trace gas observations at the GAW site Pha Din (Vietnam), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9280, https://doi.org/10.5194/egusphere-egu22-9280, 2022.

Réunion is a French island in the Indian Ocean, which holds one of the very few atmospheric observatories in the tropical Southern Hemisphere. Moreover, it hosts experiments providing both ground-based in situ and column Fourier Transform InfraRed spectrometer (FTIR) observations of CO₂, CH₄ and CO atmospheric concentrations, contributing to the Integrated Carbon Observation System (ICOS), the Network for the Detection of Atmospheric Composition Change (NDACC) and the Total Carbon Column Observing Network (TCCON). This work presents a comprehensive study of these observations made in the capital Saint-Denis and at the high-altitude Maïdo Observatory. We used simulations of the Weather Research and Forecasting model coupled with chemistry (WRF-Chem), in its passive tracer option (WRF-GHG), to gain more insight in the factors that determine these concentrations. Additionally, this study provides an evaluation of the WRF-GHG performance in a region where it has not yet been applied.

This presentation discusses the model set-up and the main findings from the comparisons between the observations and the model simulations, as summarized hereafter.

A comparison of the meteorology near the surface and along atmospheric profiles showed that WRF-GHG has decent skill in reproducing these measurements, especially temperature. Surface CO₂ in Saint-Denis follows a distinct diurnal cycle with values up to 450 ppm at night, driven by local anthropogenic emissions, boundary layer dynamics and accumulation due to low wind speeds. Due to an overestimation of local wind speeds, WRF-GHG underestimates this nocturnal buildup. At Maïdo, a similar diurnal cycle is found but with much smaller amplitude. There, surface CO₂ is essentially driven by the surrounding vegetation. A high correlation was found between the hourly XCO₂ of WRF-GHG and the corresponding TCCON observations. These represent different air masses than those near the surface. They are influenced by processes from distant areas such as Africa and Madagascar. The model shows contributions from fires during the biomass burning (BB) season, but also positive biogenic enhancements associated with the dry season. WRF-GHG fails to reproduce the CH₄ observations at Réunion accurately due to a seasonal bias in the background arising from the CAMS reanalysis boundary conditions. Further, local anthropogenic fluxes are the largest source influencing the surface observations at Réunion. However in Saint-Denis, and even more so at Maïdo, the anthropogenic CH₄ emissions from EDGAR are likely overestimated. WRF-GHG is able to simulate the CO levels at Réunion with a relative high degree of accuracy. As to the observed XCO, the importance of BB plumes from Africa and elsewhere for explaining the observed variability is confirmed. The surface observations at Maïdo can detect anthropogenic signals from the coastlands during the day and BB enhancements from afar at night, when the Observatory is located in the boundary layer and the free troposphere, respectively.

The high model resolution of 2km is needed to accurately represent the surface observations. Because of the complex topography and local dynamics, an even higher resolution might be needed at Maïdo. To simulate the column observations on the other hand, a model resolution of 50km might already be sufficient.

How to cite: Callewaert, S., Brioude, J., Duflot, V., Langerock, B., Mahieu, E., and De Mazière, M.: Exploitation of greenhouse gas observations at Ile de la Réunion using WRF-Chem simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5260, https://doi.org/10.5194/egusphere-egu22-5260, 2022.

Since December 2011 the Radiation Explorer in the Far Infrared (REFIR) Fourier trasform spectroradiometer has been operating continuously from the Italian-French station Concordia, in the Dome C region, Antarctica,  providing a decade long dataset of spectrally resolved atmospheric downwelling radiances in the mid/far-infrared range.

In 2016 The Dome C Tropospheric Observatory (DOCTOR) project was established with the aim to recalibrate and reorganize the full time series of REFIR spectra in order to provide a homogeneous dataset, and to make it available to the scientific community.

A further objective of the DOCTOR project has been to integrate the REFIR spectroradiometer with a Lidar sensor to provide coincident, colocated measurements of tropospheric backscatter profiles.

The downwelling radiance spectra are processed with a retrieval code which is capable to provide vertical profiles of tropospheric temperature and water vapor. The availability of coincident backscatter profiles permits to improve the performance of the retrieval in cloudy sky conditions, providing the vertical structure of clouds which is not easily inferred from the spectra alone.

The resulting observation repository will provide a relevant source of information about tropospheric trends in a region, the East Antarctic plateau, which is sparsely covered by ground-based measurements.

How to cite: Bianchini, G., De Pas, M., Di Natale, G., Prevedelli, M., and Palchetti, L.: 10 years of characterization of the troposphere in the East Antarctic plateau region using a ground-based Fourier transform spectroradiometer, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4366, https://doi.org/10.5194/egusphere-egu22-4366, 2022.

The Western Pacific Region has some of the highest sea surface temperatures in the world, described as the Tropical Warm Pool (TWP). It plays a major role in the troposphere-stratosphere exchange and, the chemical composition in the TWP will greatly affect that in the Tropical Tropopause Layer (TTL) and therefore the stratosphere. The FTIR station in Koror, Palau (7.5°N, 134°E) is the only FTIR site in the Warm Pool, which was installed as part of the EU-project StratoClim in 2016. The FTIR station in Paramaribo, Suriname (5.8°N, 55°W) was established as part of the EU-program STAR in 2004. The measurement site in Burgos, Philippines (18.5°N, 120.65°E) (Velazco et al., 2017a) just beside the Warm Pool was installed in 2016. Our analysis of FTIR methane measurements at Palau from 11/2018 – 06/2021 and at Suriname from 01/2017 – 05/2021 with the GEOS-Chem model simulations give some insights into transport processes and the origin of air mass in the TWP. The NDACC retrieved CH₄ has good sensitivity to the troposphere and stratosphere. Tropospheric and stratospheric X_CH4 are analyzed separately based on the FTIR measurements. Simulations of CH₄ from the GEOS-Chem model are used to be compared with the measurements from two tropical sites. The position of the Chemical Equator (Hamilton et al., 2008) calculated from the GEOS-Chem model simulations and FLEXPART are used to investigate the seasonal variations of the CH₄ measurements from FTIR.

How to cite: Sun, X., Palm, M., and Notholt, J.: The Origin of Tropospheric Air Masses and related transport processes infer from FTIR measurements and Model Simulations in Western Pacific Region and South America, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5112, https://doi.org/10.5194/egusphere-egu22-5112, 2022.

In order to monitor the contribution of different regions to the atmospheric concentrations of climate-altering gases, the estimate of the atmospheric gas emissions is regularly performed by governmental agencies and is reported into emission inventories. These “bottom-up” emission inventories are generally obtained using country-specific activity data (like population density, land  use, fuel consumptions etc.) and source-specific emission factors. However, these emission estimates can be subjected to large uncertainties, especially for non-CO₂ GHGs. This is particularly true for methane (CH₄) and some further studies based on the use of atmospheric observations are required in order to provide more precise emissions and/or to validate existing estimations.

Since 2018, hourly mean concentrations of CH₄ and CO are produced by using CRDS technique at the Mt. Cimone WMO/GAW global station (CMN, 2165 m a.s.l., Italy) in the framework of ICOS-RI (Integrated Carbon Observation System). Being overlooking the Po basin, atmospheric observations at this measurement site can be used to investigate anthropogenic emissions occurring over this densely inhabited and industrialized region.

In this work, we will present the atmospheric variability of CH₄ and CO at CMN during the period May 2018 – December 2020 as obtained from the ICOS dataset ⁵. Then, we investigate the possibility to use these observations for evaluating the uncertainty related with bottom-up inventories of CH₄ emissions over the Po basin. In particular, as based on the approach proposed by Kuwayama et al. ³ , hourly data of CH₄ and CO are fitted in order to extract the CH₄/CO ratio for each month and each year. Then, the CH₄ emissions in the Po basin are estimated by combining the observed CH₄/CO ratio with the CO emission extracted by the “state-of art” emission inventories EDGAR (Emissions Database for Global Atmospheric Research) v5.0 and v6.0 ^1,2 and compared with the national bottom-up inventory ⁴ produced by ISPRA (Istituto Superiore per la Protezione e la Ricerca Ambientale).

A critical assessment of strengths and caveats of this methodology will be provided and we present the results of sensitivity tests related to the use of different sub-setting of the CMN dataset (in term of observation time and wind direction), to the different methodologies used for CH₄/CO calculation, to the ability of the measurement site to be representative for the investigated emission region.

The obtained results show a good agreement with the inventory based emission estimations (both EDGAR and ISPRA)

References

¹ European Commission Joint Research Center. Global Air Pollutant Emissions v5.0. https://edgar.jrc.ec.europa.eu/index.php/dataset_ap50, 2019.  

² European Commission Joint Research Center. Global greenhouse gas emissions v6.0. https://edgar.jrc.ec.europa.eu/index.php/dataset_ghg60, 2020.

³ Kuwayama T. et al. , Source Apportionment of Ambient Methane Enhancements in Los Angeles, California, To Evaluate Emission Inventory Estimates. Environmental Science & Technology, 2019.

⁴ Istituto Superiore per la Protezione e la Ricerca Ambientale. Disaggregazione dell’inventario nazionale. http://emissioni.sina.isprambiente.it/serie-storiche-emissioni/, 2021.

⁵ ICOS RI. ICOS Atmosphere Release 2021-1 of Level 2 Greenhouse Gas Mole Fractions of CO2, CH4, N2O, CO, meteorology and 14CO2 (1.0). https://doi.org/10.18160/WJY7-5D06, 2021

How to cite: Fratticioli, C., Trisolino, P., Cristofanelli, P., and Calzolari, F.: Continuous measurements of the CH4/CO ratio at the remote site of Mt.Cimone and their application for the estimate of regional CH4 emissions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5736, https://doi.org/10.5194/egusphere-egu22-5736, 2022.

 Quantifying greenhouse gas (GHG) emissions in the megacities is important to mitigating climate change. To characterize the vehicle emissions which is one of the largest contributors to anthropogenic greenhouse gas emissions, we collected air samples from the entry and exit points of the Sang-do Tunnel in Seoul, South Korea in 2021, and measured dry molar mixing ratios of major greenhouse gases spices emitted from vehicles (CO₂, CH₄, and N₂O). The N₂O:CO₂ emission molar ratio from vehicles is 3.82 ± 0.39 × 10^-5, being within a range of 1.8 – 18.7 × 10^-5 previously reported in Germany, Switzerland, Sweden, and the USA. The CH₄:CO₂ emission molar ratio from the vehicles is 33.52 ± 0.43 × 10^-5, which is significantly greater than those observed in Switzerland and the USA of 4.6 ± 0.2 × 10^–5 and 15 ± 4 ×10^–5, respectively. Compared with the calculated Further, we also analyzed δ¹⁵N and δ ¹⁸O values of N₂O from the tunnel air. The δ¹⁵N and δ ¹⁸O values of N₂O emitted from the vehicles are estimated as The newly measured data from Seoul may help us better understand greenhouse gas emissions from vehicles in megacities.

How to cite: Kim, J., Ahn, J., and Ghosh, S.: Greenhouse gas emitted from vehicles in Seoul megacity, South Korea: Molar ratios (N2O:CO2, CH4:CO2) and stable isotopic compositions of N2O, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3330, https://doi.org/10.5194/egusphere-egu22-3330, 2022.

As the most effective multinational environmental agreement (MEA), the Montreal Protocol on Substances that Deplete the Ozone Layer has eliminated the production of about 98% of the ozone-depleting substances (ODSs). Moreover, the most recent Kigali Amendment to the Montreal Protocol will phase down the production of hydrofluorocarbons (HFCs) with high global warming potentials. The use of ODSs and HFCs as feedstocks is currently exempted from the control of the Montreal Protocol and its associated amendments because it was falsely assumed that there were no feedstock emissions and that products made from feedstocks were safe in manufacture, use and disposal.

In this paper, we demonstrate a previously missing mechanistic link between ODS and HFC feedstocks and a variety of chemical products that resist environmental degradation, including fluoroplastics and elastomers. We illustrate chemical reaction pathways where specific ODS and HFC gaseous molecules are made into a multitude of macromolecules that pollute the atmospheric, terrestrial and aquatic environments and harm industry workers during the manufacture. For example, the feedstock HCFC-22, itself made from chloroform (an associated feedstock), can be made into polytetrafluoroethylene (PTFE), a fluoroplastic in widespread use. Fluoropolymers’ extreme persistence in the environment and harmful emissions associated with their manufacture and disposal justify curtailing the upstream production of plastics from ODS and HFC feedstocks. We show that a variety of feedstock molecules and their byproducts go into the atmosphere and may alter atmospheric chemical composition.

These reaction mechanisms suggest that ODS and HFC feedstocks be narrowed in their exemptions under the Montreal Protocol, via further amendments and adjustments. Considering also the global warming potential and ozone depletion potential of these feedstocks, this policy response can help mitigate stratospheric ozone depletion, climate change and plastics pollution.

How to cite: Wei, Y. and Gao, S.: Underlying reaction mechanisms support narrowing exemptions of ODS and HFC feedstocks under the Montreal Protocol, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7003, https://doi.org/10.5194/egusphere-egu22-7003, 2022.

Two decades ago, concentration of ozone-depleting substances in the middle atmosphere started a slow decline as a result of the Montreal Protocol. Since then, stratospheric ozone recovery is expected and has already been observed over some parts of the world, e.g. the Antarctic. Over the mid-latitudes however, the situation is less obvious, and ozone recovery seems to differ depending on the altitude and the geographical area of interest. In view of these uncertainties, there is still a strong need for high-quality and long-term ozone observations and their validation.

Switzerland has a number of stations monitoring ozone using different techniques. In particular, it is the only place in the world with two collocated ground-based ozone microwave radiometers. Located less than 50 km apart, they provide continuous hourly ozone profiles in the middle-atmosphere (~20 to 75 km) since more than 20 years with very few interruptions. Both instrument are part of the Network for the Detection of Atmospheric Composition Change (NDACC) and are regularly used for ozone trend studies or cross validation of satellite observations over Central Europe.

Despite the many studies conducted with these instruments, some anomalous periods and discrepancies in trends were recently identified in their time series. To address these problems, a full harmonization and reprocessing of the data was performed with the aim of obtaining two improved and independent time series. This harmonization affects the calibration of the radiometric measurements, flagging procedures and the retrievals of atmospheric profiles and has now been completed for the last decade.

In this contribution, we present and compare the new harmonized ozone time series for both instruments and highlight the improvements in the ozone retrievals compared to the old data processing. We also perform a comparison of these new data series against measurements from the Microwave Limb Sounder and the Solar Backscatter Ultraviolet Radiometer over Switzerland. As an additional validation, we show some first results of diurnal cycles derived from the new harmonized data series and compare it with model-based diurnal ozone climatology.

How to cite: Sauvageat, E., Maillard Barras, E., Hocke, K., Haefele, A., and Murk, A.: Long-term harmonized ozone profiles in the middle atmosphere over Switzerland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5107, https://doi.org/10.5194/egusphere-egu22-5107, 2022.

Sudden stratospheric warmings (SSWs) are dynamic events associated with the rise in stratospheric temperature and the reversal in zonal mean zonal winds. SSWs are driven by large-scale planetary waves that propagate to the stratosphere. These large-scale waves are produced in regions of variable topography such as mountains or due to temperature differences at the warm ocean - cold landmass interfaces. The breaking of the planetary waves propagated to the stratosphere leads to the deceleration and perturbation of the polar vortex circulation, resulting in the sudden increase in polar stratospheric temperature. Due to the highly variable nature of the topography, the northern hemispheric polar vortex is more disturbed by planetary waves than the southern hemisphere. Far more stable winters are seen in the southern hemisphere, with the Antarctic polar vortex in concentric alignment with the south pole terminator.

Despite the usual stability of the southern hemisphere and the infrequency of SSW events, the dynamic event of 2019 was rare and strong, following the likes of the 2002 southern hemispheric SSW. The 2019 SSW event occurred around 29 August and spanned close to three weeks, increasing stratospheric temperature and O₃ (ozone) concentration. In this study, we investigate the impacts of the 2019 SSW on the stratosphere using the Solar Occultation for Ice Experiment (SOFIE) instrument onboard the Aeronomy of Ice in the Mesosphere (AIM) spacecraft and other measurements.

SOFIE uses solar occultation to measure solar energy passing through the limb of the earth’s atmosphere at sunrise and sunset. Measurements are typically made at high latitudes (65^o-85^o N/S) with a vertical field-of-view of ~ 1.6 km covering wavelengths from 0.29 to 5.26 microns. Temperature measurements from SOFIE in 2019 indicate that the average stratospheric temperature during mid-September was higher than in the past years in the 20-30 km altitude range, attributed to the exceptional meteorology during August and September.

In the springtime, stratospheric O₃ depletion occurs when polar stratospheric clouds (PSCs) convert halogen reservoir species into O₃-destroying reactive forms. The sharp increase in stratospheric temperature during SSWs evaporates PSCs and prevents halogen activation, thus, inhibiting O₃ destruction. PSCs are composed of HNO₃ (nitric acid) and H₂O (water). HNO₃ is formed by water reacting with NO₂ (nitrogen dioxide), formed by the oxidization of NO (nitric oxide). Thus, using NO and H₂O (from SOFIE) as proxies for HNO₃, we deduce that both species were higher in 2019 after the SSW than past years’ average during the same period. This indicates a lesser loss of HNO₃  to PSCs through denitrification. Consequentially, SOFIE O₃ in 2019 (August – mid-October) is significantly higher than the past years’ average, indicating a smaller O₃ hole, also reported by NASA O₃ watch (for 7 September- 13 October).

This study investigates the 2019 Antarctic O₃ enhancement and analyzes the underlying chemistry and mechanism using SOFIE and other measurements.  

How to cite: Das, S., Bailey, S. M., and Thurairajah, B.: Investigation of the Ozone Enhancement during the 2019 Sudden Stratospheric Warming in the Southern Hemisphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6083, https://doi.org/10.5194/egusphere-egu22-6083, 2022.