AS3.7

Plastic pollution is one of the most pressing environmental and social issues of the 21^st century. Recent work has highlighted the atmosphere’s role in transporting microplastics to remote locations. Here we use in situ observations of microplastic deposition combined with an atmospheric transport model and optimal estimation techniques to test hypotheses of the most likely sources of atmospheric plastic. Results suggest that atmospheric microplastics in the western USA are primarily derived from secondary re-emission sources including roads, the ocean and agricultural soil dust. Using our best estimate of plastic sources and modeled transport pathways, most continents were net importers of plastics from the marine environment, underscoring the cumulative role of legacy pollution in the atmospheric burden of plastic. This effort is the first to use high resolution spatial and temporal deposition data along with several hypothesized emission sources to constrain atmospheric plastic. Akin to global biogeochemical cycles, plastics now spiral around the globe with distinct atmospheric, oceanic, cryospheric, and terrestrial lifetimes. Though advancements have been made in the manufacture of biodegradable polymers, our data suggest that extant non-biodegradable polymers will continue to cycle through the Earth’s systems. Due to limited observations and understanding of the source processes, there remain large uncertainties in the, transport, deposition, and source attribution of microplastics. Thus, we prioritize future research directions for understanding the plastic cycle.

How to cite: Mahowald, N., Brahney, J., Prank, M., Cornwell, G., Klimont, Z., Matsui, H., and Prather, K.: Constraining the atmospheric limb of the plastic cycle, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16473, https://doi.org/10.5194/egusphere-egu21-16473, 2021.

Eleven billion tons of plastic are projected to accumulate in the environment by 2025. Because plastics are persistent, they fragment into pieces that are susceptible to wind entrainment. Using high resolution spatial and temporal data we tested whether plastics deposited wet versus dry have unique atmospheric life histories. Further, we report on the rates and sources of deposition to remote U.S. conservation areas. We show that urban centers and resuspension from soils or water are important sources for wet deposition. In contrast, plastics deposited dry were smaller in size and rates were related to indices that suggest longer range or global transport. Deposition rates averaged 132 plastics m^-2 day^-1 amounting to > 1000 tons of plastic deposition to western U.S. protected lands annually.

How to cite: Brahney, J., Hallerud, M., Heim, E., Hahnenberger, M., and Sukumaran, S.: Wet and dry plastic deposition in the western United States, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16331, https://doi.org/10.5194/egusphere-egu21-16331, 2021.

Since the first reports on the presence of plastic debris in the marine environment in the early 70s (1), plastics have been steadily accumulating in the environment. The global production of plastics in 2019 reached 368 Mt (from 311 Mt in 2014 and 225 Mt in 2004), with the largest portion produced in Asia (51%) (2), whereas 10% is believed to end into the sea every year (3). As a result, plastics have been confirmed today in several freshwater (4), and terrestrial (5) ecosystems; they fragment into microplastics (MPs, 1 µm to 5 mm) (6) and nanoplastics (<1µm) (7) via physical processes (8). MP present has been now confirmed from the Alps (9) and the Pyrenees (10), as far as Antarctica (11) and the high Arctic (9). Consequently, MPs have been found to
affect coral reefs (12), marine (13) and terrestrial animals (14). Schwabl et al. (15) detected them in human stool, while a recent study by Ragusa et al. (16) reported that MPs were even found in all placental portions.
A smaller fraction of MPs originates from road traffic emissions (17). Kole et al. (18) reported global average emissions of tire wear particles (TWPs) of 0.81 kg year-1 per capita, about 6.1 million tonnes (~1.8% of total plastic production). Emissions of brake wear particles (BWPs) add another 0.5 million tonnes. TWPs and BWPs are produced via mechanical abrasion and corrosion (19). Here, we present global trends in emissions, transport and deposition of road MPs.

References:
1. Colton, J. B., et al. Science (80). 185, 491–497 (1974).
2. PlasticsEurope. https://www.plasticseurope.org/en/resources/market-data (2019).
3. Mattsson, K., et al. Impacts 17, 1712–1721 (2015).
4. Blettler, M. C. M., et al.Water Res. 143, 416–424 (2018).
5. Chae, Y. & An, Y. J. Environ. Pollut. 240, 387–395 (2018).
6. Peeken, I. et al. Nat. Commun. 9, (2018).
7. Wagner, S. & Reemtsma, T. Nat. Nanotechnol. 14, 300–301 (2019).
8. Gewert, B., et al. Environ. Sci. Process. Impacts 17, 1513–1521 (2015).
9. Bergmann, M. et al. Sci. Adv. 5, 1–11 (2019).
10. Allen, S. et al. Nat. Geosci. 12, 339–344 (2019).
11. González-Pleiter, M. et al. Mar. Pollut. Bull. 161, 1–6 (2020).
12. Lamb, J. B. et al. P Science (80-. ). 359, 460–462 (2018).
13. Wilcox, C., et al. Sci. Rep. 8, 1–11 (2018).
14. Harne, R. J. Anim. Res. 383–386 (2019) doi:10.30954/2277-940x.02.2019.25.
15. Schwabl, P. et al. Ann. Intern. Med. 171, 453–457 (2019).
16. Ragusa, A. et al. Environ. Int. 146, 106274 (2021).
17. Schwarz, A. E., et al. Mar. Pollut. Bull. 143, 92–100 (2019).
18. Jan Kole, P., et al. Int. J. Environ. Res. Public Health 14, 1–4 (2017).
19. Penkała, M., et al. Environments 5, 9 (2018).

How to cite: Evangeliou, N., Grythe, H., Kylling, A., and Stohl, A.: Global emission, atmospheric transport and deposition trends of microplastics originating from road traffic, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16513, https://doi.org/10.5194/egusphere-egu21-16513, 2021.

Atmospheric plastic pollution is now a global problem. Microplastics (MP) have been detected in urban atmospheres as well as in remote and pristine environments, showing that suspension, deposition and aeolian transport of MP should be included and considered as a major transport pathway in the plastic life cycle. Due to the limitations in sampling and instrumental methodology, little is known about MP and nanoplastics (NP) with sizes lower than 50 µm, which is the current limit for FT-IR and Raman microscopy. In our recent work [Bianco et al. 2020], we describe how NP could be transported for longer distances than MP, making them globally present and potentially more concentrated than MP. We highlight that it is crucial to explore new methodologies to collect and analyse NP.

Small MPs can be detected by fluorescence spectroscopy: for example, particles can be efficiently stained using Nile Red, as described by Erni-Cassola et al. [2017]. This hydrophobic dye shows fluorescence in green and yellow range of the electromagnetic spectrum and can be easily detected also at low concentration. We are developing a new method, based on this principle, to detect MPs in natural matrices. These are, for instance, surface and atmospheric waters, containing dissolved organic matter and suspended organic particles. Preliminary results on polyethylene, polystyrene and polyvinylchloride are promising for particles in the range 1-25 µm suspended in MilliQ water. We are currently testing the method on river water and snow.

Bianco, A.; Passananti, M. Atmospheric Micro and Nanoplastics: An Enormous Microscopic Problem. Sustainability 2020, 12, 7327.

Erni-Cassola, G.; Gibson, M.; Thompson, R.; Christie-Oleza, J. Lost, but Found with Nile Red: A Novel Method for Detecting and Quantifying Small Microplastics (1 mm to 20 μm) in Environmental Samples. Environ. Sci. Technol. 2017, 51, 23, 13641–13648

How to cite: Bianco, A., Sordello, F., Ehn, M., Vione, D. V., and Passananti, M.: Atmospheric transport of micro and nanoplastics and fluorescence detection of particles < 20 µm, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3914, https://doi.org/10.5194/egusphere-egu21-3914, 2021.

In April 2017, the A-LIFE aircraft field experiment (Absorbing aerosol layers in a changing climate: aging, lifetime and dynamics; (www.a-life.at) was carried out in the Eastern Mediterranean. The overall goal of the ERC-funded A-LIFE project is to investigate the properties of mixtures of absorbing aerosols (in particular mineral dust and black carbon) during their atmospheric lifetime to gather a new data set of key parameters of absorbing aerosol mixtures, to investigate their microphysical and optical properties, and to study potential links between the presence of absorbing particles, aerosol layer lifetime and particle removal.

In 22 research flights (~80 flight hours), several outbreaks of Saharan and Arabian dust, as well as pollution, biomass burning, and dust-impacted clouds were studied, and a unique aerosol and cloud data set was collected. During a number of flights, coordinated observations including overflights of the ground-based sites in Cyprus (Limassol, Paphos, Agia Marina), Crete (Finokalia), and over Austria (Vienna, Sonnblick Observatory) were performed. The A-LIFE campaign was carried out in close coordination with the 18-month field observations conducted in the framework of CyCARE (October 2016 – March 2018) organized by the Leibniz Institute for Tropospheric Research, and with the PreTECT initiative of the National Observatory of Athens.

To perform source apportionment, the Lagrangian transport and dispersion model FLEXPART (FLEXible PARTicle dispersion model) version 8.2 was used. Based on FLEXPART model results and aerosol measurements, the observations were classified into 12 aerosol types including background aerosol, clean and polluted mixtures without coarse mode aerosol as well as three sub-classes (clean, moderately-polluted and polluted) for Saharan dust, Arabian dust and mixtures with coarse mode. For each of the 12 aerosol classes, microphysical and optical aerosol properties were derived. One surprising finding of A-LIFE is that scattering properties of polluted dust aerosol do not show the typical dust signature, but rather show a wavelength-dependency of the scattering coefficient.

We will give an overview of the A-LIFE field experiment and available data sets, compare the properties of the different aerosol mixtures, and discuss the question which aerosol component (natural vs. anthropogenic) dominates the properties in mixed aerosols. We will also compare the A-LIFE dust observations with results from other field experiments (SAMUM, SALTRACE, ATom).

Acknowledgements: This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 640458 (A-LIFE). Two EUFAR projects clustered with A-LIFE provided funding for 16 additional flight hours. We would also like to thank the University of Vienna, LMU and DLR for a significant amount of funding for instrumentation, aircraft certification costs, extra flight hours and aircraft allocation days.

How to cite: Weinzierl, B. and the A-LIFE Science Team: The A-LIFE field experiment in the Eastern Mediterranean - Overview and selected highlights , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16129, https://doi.org/10.5194/egusphere-egu21-16129, 2021.

Airborne particulate matter such as mineral dust comes mainly from natural sources, and the arid regions of Sahara and Sahel in Africa release large amounts of the aerosols dispersed worldwide. There is evidence of concomitant presence of desert dust particles and bioaerosols such as pollen grains in the atmosphere, which produce a significant decline in air quality during the dust intrusions events. However, there is little knowledge about the influence of dust episodes on pollen exposure in allergy sufferers as well as the causes that may produce a potential effect of the intrusions on airborne pollen levels. This potential effect on the airborne pollen concentrations is analysed in the Iberian Mediterranean region in this study. Mediterranean countries are strongly affected by Saharan-Sahel dust intrusions, and the Iberian territory, specially the central and southern areas, suffer frequently great incidence of dust episodes due to its geographic location. In this study firstly, the simultaneous occurrence between airborne pollen peaks and Saharan-Sahel dust intrusions were analysed and compared with the behaviour in the days before and after the dust intrusions in the central and south-eastern Iberian Peninsula. Secondly, the weather conditions favouring high pollen concentrations during dust episodes namely prevalent winds, air mass pathways and variations in other meteorological variables like air temperature, relative humidity or atmospheric pressure were studied.

Pollen peaks often coincided with dust episodes during the pollen season in the central Iberian Peninsula. The increase of the airborne pollen concentrations during the dust episodes is clear in inland Iberian areas, although this was not the case in coastal areas of the southeast where pollen concentrations could even be seen to decrease when easterly winds from the sea prevailed during dust intrusions. Total pollen concentrations and also pollen types such as Olea, Poaceae and Quercus showed an increase in the central Iberian Peninsula during the dust episodes when two meteorological phenomena occurred simultaneously: 1) prevailing winds came from large areas of the main wind-pollinated pollen sources at medium or short scale (mainly from western and southwestern areas); and 2) optimal meteorological conditions that favoured pollen release and dispersal into the atmosphere (mainly high temperatures and low humidity). Both these conditions often occur during Saharan-Sahel dust intrusions in the centre. The findings suggest that the proportion of long-range transport is lower than those produced in medium and short distance by dust intrusions of air masses. Therefore, maximum pollen peaks are most likely to occur during dust episodes in the central Iberian Peninsula dramatically increasing the risk of outbreaks of pollinosis and other respiratory diseases in the population. The negative effects of the mineral dust on public health are well known, even more so when allergenic biological agents are co-transported together by the air mass movements coming from desert areas. The findings of this study have very relevant implications for defining health-emergency alerts for severe Saharan-Sahel dust outbreaks.

How to cite: Rojo, J., Moreno, J. M., Romero-Morte, J., Lara, B., Elvira-Rendueles, B., Negral, L., Fernández-González, F., Moreno-Grau, S., and Pérez-Badia, R.: Influence of Saharan-Sahel dust outbreaks on pollen exposure in the Iberian Mediterranean areas, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6750, https://doi.org/10.5194/egusphere-egu21-6750, 2021.

Soil dusts are an important source of aerosol in agricultural regions and can affect the Earth’s radiation budget through the modification of cloud properties, and in particular, through their ability to act as ice nucleating particles. In order to impact cloud properties, agricultural soil dusts need to be transported from the point of emission to cloud-relevant altitudes. Vertical transport within the planetary boundary layer is strongly controlled by turbulence and is challenging to represent accurately in regional and global models. Large-eddy simulations (LES) are run at resolutions capable of resolving most of the turbulent energy directly and can thus better simulate vertical transport. In this study, we leverage the LES ARM Symbiotic Simulation and Observation (LASSO) large-eddy simulations to simulate vertical transport of agricultural dust within the turbulent boundary layer using a modified version of the stochastic dispersion model FLEXPART-WRF. We find that the modified model is better capable of simulating particle transport due to turbulence, and that particle size was the greatest factor in determining particle lifetime. Individual meteorology and particle density had intermediate effects upon particle transport, while release height had little effect upon simulation results. Finally, we utilize a quasi-single column model (QSCM) approach to determine how our results compare to a parameterized treatment of turbulence. The QSCM simulations led to greater tracer transport out of the boundary layer, with ramifications for any studies utilizing a Lagrangian stochastic model to understand tracer dispersion. These results highlight the importance of accurately simulating turbulence for understanding particle transport.

How to cite: Cornwell, G., Xiao, H., Berg, L., and Burrows, S.: Simulated dust transport in the convective boundary layer , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6729, https://doi.org/10.5194/egusphere-egu21-6729, 2021.

In the Mediterranean region, climate change-induced effects (i.e., increasing drought and heatwaves) are intensifying wildfire occurrences and severity. During 2017 the administrative region of Calabria (southern Italy) was affected by an exceptional wildfire season. This study evaluates the wildfire impact on some air quality parameters in two National Parks, located in the north and south of the region, respectively. Two sampling stations were considered for the impact assessment, namely the Monte Curcio Global Atmosphere Watch (GAW) regional station, located in the Sila National Park, and the Mammola rural-regional background station of the Regional Environmental Protection Agency of Calabria (ARPACal), in the Aspromonte National Park. To evaluate wildfire impact, a method based on the integration of ground-based observations (i.e., PM_2.5, PM₁₀, EBC, CO, and fire location) and WRF-HYSPLIT back-trajectories was applied. The WRF-HYSPLIT coupling allowed to reproduce high-resolution back-trajectories, improving the model accuracy in a complex orographic region such as the study area. Furthermore, wildfire impact on human health was qualitatively evaluated in terms of passively smoked cigarettes (PSC), related to the measured PM_2.5 concentrations. During the examined period (summer 2017), the exposure to wildfire emissions resulted equivalent to approximately 6 PSC per day, for both stations. These outcomes, obtained at the regional scale in southern Italy, highlight that wildfire emissions, whose associated risks are still underestimated, are of concern for human health even in protected areas. Future studies, based on a more thorough chemical characterization and source apportionment methods, should be oriented towards assessing the wildfire contribution to air quality deterioration.

How to cite: Castagna, J., Senatore, A., Bencardino, M., D'Amore, F., Sprovieri, F., Pirrone, N., and Mendicino, G.: Wildfire impact assessment through air quality monitoring in natural conservation areas and WRF-HYSPLIT coupled modelling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12811, https://doi.org/10.5194/egusphere-egu21-12811, 2021.

Black carbon (BC) particles originate from incomplete combustion of biomass and fossil fuels. They are known to contribute to the warming of Earth’s climate due to radiative effects and aerosol-cloud interactions. The lifetime of sub-micron BC in the troposphere is in the order of days-weeks. Through interaction with other airborne compounds, the hydrophobic nature of BC gradually becomes more hygroscopic and thus available as CCN.

An assessment of the large-scale impact on clouds and climate requires detailed insights about the lifecycle of BC in the atmosphere, understanding sources for BC, transport, transformation, and removal processes. All these processes are tightly linked to particle size, making knowledge regarding how BC distributes over a given size range substantial.

In a previous study we explored statistical methods to attribute BC mass according to particle size (in review). Combining these results with cluster analysis of long term record of aerosol number size distribution (NSD) observations from Zeppelin Observatory it was shown that the method produced reasonable results for a majority of observations. However, the cluster characteristic of NSD associated with high level of pollution presented additional challenges as the methodological approach gave an unrealistic average BC size distribution.

In the current study we focus on these inconsistencies; additional analytical methods are introduced to resolve source-receptor relationships, defining transport characteristics using extensive trajectory analysis. The analysis provides insights of the processes along the travel path to the receptor location and resolves key transport routes for the BC fraction to the Arctic.

How to cite: Cremer, R., Tunved, P., Partridge, D., and Ström, J.: Sources and Transport of Black Carbon number size distribution at Zeppelin Observatory, Svalbard, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7646, https://doi.org/10.5194/egusphere-egu21-7646, 2021.

Improving air quality is an important driving force for China’s move toward clean energy. Since 2017, the “coal-to-gas” and “coal-to-electricity” strategies have been extensively implemented in northern China, aiming at reducing dispersed coal consumption and related air pollution by promoting the use of clean and low-carbon fuels. Our analyses show that on top of meteorological influences, the effective emission mitigation measures achieved an average decrease of fine particulate matter (PM_2.5) concentrations of ∼14% in Beijing and surrounding areas (the “2+26” pilot cities) in winter 2017 compared to the same period of 2016, where the dispersed coal control measures contributed ∼60% of the total PM_2.5 reductions. However, the localized air quality improvement was accompanied by a contemporaneous ∼15% upsurge of PM_2.5 concentrations over large areas in southern China. We find that the pollution transfer that resulted from a shift in emissions was of a high likelihood caused by a natural gas shortage in the south due to the coal-to-gas transition in the north. The overall shortage of natural gas greatly jeopardized the air quality benefits of the coal-to-gas strategy in winter 2017 and reflects structural challenges and potential threats in China’s clean-energy transition. Our finding highlights the importance and necessity of synergy between environmental and energy policymaking to address the grand challenge of an actionable future to achieve the cobenefits of air quality, human health, and climate.

How to cite: Wang, S., Su, H., Chen, C., Tao, W., Streets, D., Lu, Z., Zheng, B., Carmichael, G., Lelieveld, J., Pöschl, U., and Cheng, Y.: Natural gas shortages during the “coal-to-gas” transition in China have caused a large redistribution of air pollution in winter 2017, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15706, https://doi.org/10.5194/egusphere-egu21-15706, 2021.

An air pollution process in Jiangsu Province, China on December 22–23, 2016 is discussed by analyzing various data set, including the meteorological observation data, the reanalysis data from National Centers for Environmental Prediction (NCEP), the Air Quality Index (AQI), the PM_2.5 and PM₁₀ concentrations data, and the airflow backward trajectory model of National Oceanic and Atmospheric Administration (NOAA). The results show that the air pollution episode was under the background of a medium cold front from the west of the Hetao area, and caused by regional transport of pollutants from North China. The primary pollutant was PM_2.5 and PM₁₀. The PM_2.5 and PM₁₀ concentrations increase significantly 4–6 h after the cold front passing and reached the peak in 13–24 h. The obvious lag phenomena of the rising period and the peak-moment of PM_2.5 and PM₁₀ concentrations were found at the Suzhou, Huai'an, Taizhou and Xuzhou stations, and the maximum of 3h-allobaric, the maximum and average values of the wind speed near the ground were larger one by one at the four stations respectively in the northwestern Jiangsu, north-central Jiangsu, along with the Yangtze river Jiangsu, and southeastern Jiangsu. The period of middle –heave level pollution in Suzhou was 7–9 h later than in Huai'an and Taizhou, and was 24 h later than in Xuzhou, because of the lower PM_2.5 and PM₁₀ concentrations at early December 21, the delay of pollutants from upstream, and the larger wind speed from the boundary layer to the surface in southeastern Jiangsu. WRF-Chem model can well reveal the pollutant transport process. The high-value zone has a close relationship with the position of cold front. At 1200 LST on December 22, the cold front reached Xuzhou accompanied by high PM_2.5 concentration. At 1400 LST on December 22, the cold front advanced to Huai'an. The high PM_2.5 concentration zone moved south alongside the cold front and covered Xuzhou and Huai'an. Suzhou, far away from the upstream, was less vulnerable to pollutant transport. The high-value did not fell until the northwest wind shifted to the north wind. The backward trajectory analysis of air pollution also indicated that regional transport of pollutants from North China led to the middle –heave level pollution weather.

How to cite: Liu, D., Gu, P., and Qian, J.: Cold Fronts Transport Features of North China Pollutant over the Yangtze River Delta, China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7854, https://doi.org/10.5194/egusphere-egu21-7854, 2021.

Black carbon (BC) affects the radiation budget of the Earth by absorbing solar radiation, darkening snow and ice covers, and influencing cloud formation and life cycle. Modelling BC in remote regions, such as the Arctic, has large inter-model variability which causes variation in the modelled aerosol effect over the Arctic. This variability can be due to differences in the transport of aerosol species which is affected by how wet deposition is modelled.

In this study we developed an aerosol size-resolved in-cloud wet deposition scheme for liquid and ice clouds for models which use a size-segregated aerosol description. This scheme was tested in the ECHAM-HAMMOZ global aerosol-climate model. The scheme was compared to the original wet deposition scheme which uses fixed scavenging coefficients for different sized particles. The comparison included vertical profiles and mass and number wet deposition fluxes, and it showed that the current scheme produced spuriously long BC lifetimes when compared to the estimates made in other studies. Thus, to find a better setup for simulating aerosol lifetimes and vertical profiles we conducted simulations where we altered the aerosol emission distribution and hygroscopicity.

We compared the modelled BC vertical profiles to the ATom aircraft campaign measurements. In addition, we compared the aerosol lifetimes against those from AEROCOM model means. We found that, without further tuning, the current scheme overestimates the BC concentrations and lifetimes more than the fixed scavenging scheme when compared to the measurements. Sensitivity studies showed that the model skill of reproducing the measured vertical BC mass concentrations improved when BC emissions were directed to larger size classes, they were mixed with soluble compounds during emission, or BC-containing particles were transferred to soluble size classes after aging. These changes also produced atmospheric BC lifetimes which were closer to AEROCOM model means. The best comparison with the measured vertical profiles and estimated BC lifetimes was when BC was mixed with soluble aerosol compounds during emission.

How to cite: Holopainen, E., Kokkola, H., Laakso, A., and Kühn, T.: In-cloud scavenging scheme for sectional aerosol modules – implementation in the framework of the Sectional Aerosol module for Large Scale Applications version 2.0 (SALSA2.0) global aerosol module, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15018, https://doi.org/10.5194/egusphere-egu21-15018, 2021.

The Lagrangian dispersion model FLEXPART v10.4 uses cloud water content, temperature, and precipitation rates to calculate wet scavenging. Currently, only precipitation fields are interpolated spatially to the particle positions. A simple nearest-neighbour approach is used for cloud parameters and temperature. This is made worse by the fact that precipitation fields from the European Centre for Medium Range Weather Forecasts (ECMWF) are temporal integrals whereas all the other parameters refer to a specific time. The pre-processor flex_extract disaggregates the precipitation fields to construct point values that can preserve the integral quantity when interpolated in FLEXPART. However, this method does not preserve precipitation in each time interval, leading to smoothing, or even shifting precipitation into dry periods.

We have implemented interpolation of all fields relevant for wet scavenging in FLEXPART v10.4 as well as the option to use our improved precipitation disaggregation scheme (https://doi.org/10.5194/gmd-11-2503-2018). It introduces two additional subgrid points within one original time interval. This secures consistency, continuity and mass conservation of precipitation within each time interval.

These updates lead to a massive improvement of the wet deposition fields in a specific test case where we applied a high-resolution outgrid that makes the effects of interpolation issues more visible. Originally, a kind of checkerboard pattern was visible, as well as a banded structure due to the finite time interval between meteorological input fields. Both features are mostly eliminated now. Additionally, the influence of varying the temporal and spatial resolution of the ECMWF input fields was investigated, and the benefit of using the ECMWF cloud water content instead of parametrised values. We also look at the impact of the new version on other, previously used test cases, for example, a lifetime analysis of aerosol particles as well as transport of mineral dust and black carbon.

How to cite: Tipka, A. and Seibert, P.: Effects of improved interpolation in the wet-scavenging scheme of FLEXPART, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15805, https://doi.org/10.5194/egusphere-egu21-15805, 2021.

This paper presents the development and application of a numerical Lagrangian model of the transport of aerosol particles in the urban boundary layer of the atmosphere with a high spatial resolution. The development of the model is motivated by the limited measurement methods for observing aerosol concentrations in urban environments, both in terms of coverage density and in terms of accuracy and representativeness. The growing interest of the world community in the problems of monitoring air pollution in cities and the atmospheric distribution of biologically active aerosols also became a motivating factor.

The model uses the equation of motion to calculate the trajectory of a particle suspended in the air. It is based on Newton's second law and takes into account the forces of gravity, buoyancy and air resistance. The influence of stochastic turbulent eddies on the particle motion is taken into account in the model by using turbulent parameterizations. The effect of turbulence is important when describing the motion of particles in this model, since aerosols have a size much smaller than the grid step of the input data and can stay inside one cell for a long time, being under the influence of subgrid vortices. In this model, three parameterizations are implemented: a simple Gaussian model, a random displacement model, and a random walk model. In all three, the pulsation velocity component is a normally distributed random variable, but in the first two parameterizations it is generated at each time step of the Lagrangian model. In the last one, the interaction time of the particle with the turbulent vortex is introduced, during which the pulsation velocity component acting on the particle remains constant, characterizing the effect of a particular vortex. Additionally, a version of the model based on the Langevin equation has been implemented to more accurately account for the effect of turbulence on particle motion.

The developed numerical model is implemented in a program code in the C++ programming language and allows one to calculate individual trajectories of motion and concentrations of particles. Input data (wind speed components, turbulence characteristics and others) can be set analytically or imported from hydrodynamic models.

The model has been successfully tested and verified on several idealized analytical solutions – an equivalence is obtained in terms of the concentration field. Experiments have also been carried out to reproduce the transport of particles in a series of urban canyons, including particles with a finite half-life that simulate the COVID-19 virions (SARS-CoV-2). Based on the results of the calculations, the influence of stratification, particle size and lifetime on the transport of aerosols in a typical urban environment was estimated.

The work is partially supported by RFBR grants 18-05-60126 and 19-05-50110.

How to cite: Varentsov, A., Stepanenko, V., and Mortikov, E.: Numerical simulation of particle transport in the boundary layer with implications for SARS-CoV-2 virions distribution in urban environments , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16126, https://doi.org/10.5194/egusphere-egu21-16126, 2021.

The identification of the baseline is an important task in inverse modeling of greenhouse gases, as it represents the influence of atmospheric chemistry and transport and surface fluxes from outside the inversion domain, or flux contributions prior to the length of the backward calculation for Lagrangian models. When modeling halocarbons, observation-based approaches are often used to calculate the baseline, although model-based approaches are an alternative. Model-based methods need global unbiased fields of mixing ratios of the observed species, which are not always easy to get and which need to be interfaced with the model used for the inversion. To find the best way to identify the baseline and to investigate whether the usage of observation-based approaches is suitable for inverse modeling of halocarbons, we use and analyze a model-based and two frequently used observation-based methods to determine the baseline and investigate their influence on inversion results. The model-based method couples global fields of mixing ratios with backwards-trajectories at their point of termination. We simulate those global fields with a Lagrangian particle dispersion model, FLEXPART_CTM, that uses a nudging routine to relax model data to observed values. The second method under investigation is the robust estimation of baseline signal (REBS) method, that is purely based on statistical analysis of observations. The third analyzed method is also primarily observation-based, but uses model information to subtract prior simulated mixing ratios from selected observations. We apply those three methods to sulfur hexafluoride (SF₆) and use the Bayesian inversion framework FLEXINVERT for the inverse modeling and the Lagrangian particle dispersion model FLEXPART to calculate the source-receptor-relationship used in the inversion.

How to cite: Vojta, M., Thompson, R., Groot Zwaaftink, C., and Stohl, A.: Inverse modeling of halocarbons: sensitivity to the baseline definition, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4029, https://doi.org/10.5194/egusphere-egu21-4029, 2021.

Measurements of trace gas concentrations and their fluxes are essential to investigate source regions of greenhouse gases (GHGs) and other pollutants. Most flux towers provide observations at heights of several meters to tens of meters and therefore provide information about possible flux sources on a local spatial scale. Here we present an analysis of trace gas concentration and flux measurements from one of the few European tall towers located close to Beromünster, Switzerland. The tower was initially set up as a CarboCount CH site — a dense GHG observation network run for four years (2012 - 2015) — and is continued since by the University of Bern. The presented measurements are taken at an altitude of 212m above ground. This relatively high observation height results in a flux footprint of the tower of many kilometers and therefore the tower observations are predestined for a source analysis on a much larger scale than typical for flux towers. We analyze subsets of the available time series selected by season, time of day, wind direction, and other criteria. In a first step, the field of view of the tower for these subsets is estimated with a flux footprint parameterization. This is followed by a correlation analysis between various observations. Results indicate particularly high trace gas concentrations during periods of lowered planetary boundary layer heights and wind coming from the Zurich metropolitan area. In a next step we intend to perform a field of view analysis with a Lagrangian atmospheric transport model (Flexpart).

How to cite: Plach, A., Stohl, A., and Leuenberger, M.: High trace gas concentrations during lowered boundary layer heights at a Swiss tall tower site, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4451, https://doi.org/10.5194/egusphere-egu21-4451, 2021.

Synthetic greenhouse gases contribute currently about 10% to anthropogenic radiative forcing, and their future impact depends on the replacement of compounds with long lifetimes by compounds with short lifetimes and negligible global warming potential (GWP). Furthermore, chlorine and bromine-containing synthetic gases are the drivers of stratospheric ozone destruction. Therefore, observing the atmospheric abundance of synthetic gases and quantifying their emission sources is critical for predicting their related future impacts and assuring successful regulation.

Regional-scale atmospheric inverse modeling can provide observation-based estimates of greenhouse gas emissions at a country and continental scale and, consequently, support the process of forecasting and regulation. Inverse modeling is based on three main components: Source sensitivities derived from atmospheric transport models, observations, and an inversion framework. Within the Swiss National Science Foundation project IHALOME (Innovation in Halocarbon Measurements and Emission Validation) we increase the spatial resolution of the Lagrangian particle dispersion model FLEXPART-COSMO from 7 km to 1 km in order to enhance localization of Swiss halocarbon emissions based on newly available observations from the Swiss Plateau at the Beromünster tall tower. The transport model is driven by the meteorological fields of the regional numerical weather prediction model (NWP) COSMO run at MeteoSwiss.

The higher-resolution model exhibits increased three-dimensional dispersion, and as a result, is unable to reproduce the variability seen in the observations and in the 7 km model at the tall tower site Beromünster for a well-studied validation tracer (methane). Because the TKE (Turbulent Kinetic Energy) values do not differ significantly between the two model versions, head-to-head comparisons of parameterized turbulence cannot fully explain the concentration discrepancies. Comparisons of wind fluctuations resolved on the grid-scale suggest that the dispersion differences may originate from a duplication of turbulent transport, on the one hand, covered by the high-resolution grid of the Eulerian model and, on the other hand diagnosed by FLEXPART's turbulence scheme. In an attempt to tune FLEXPART-COSMO’s turbulence scheme at high resolution, we scale FLEXPART's parameterized turbulence so it matches the TKE computed in COSMO. Test simulations with the scaled FLEXPART turbulence show remarkable improvements in the high-resolution model's ability to predict the observed tracer variability and concentration at the Beromünster tall tower. We further introduce new equations in FLEXPART's turbulence scheme for each component of the variations of the winds in order to mimic the TKE produced by the turbulence scheme of COSMO and hence resolve the part of the turbulence spectrum which is unresolved by the high-resolution model. Compared to the coarse resolution simulations, simulations with scaled turbulence result in a more realistic and pronounced diurnal cycle of the tracer and overall improved correlation with observations.

Concluding, the increasing resolution of NWP models may lead to the representation of the part of the turbulence spectrum by the models themselves. In these models, big eddies (most likely related to convection) are partly resolved and do not require additional parameterization. The turbulence schemes of the past, developed for coarse resolution models, should be revisited to include this effect.

How to cite: Katharopoulos, I., Rust, D., Vollmer, M. K., Reimann, S., Emmenegger, L., Brunner, D., and Henne, S.: The impact of turbulence parameterization in high-resolution inverse modeling of synthetic greenhouse gases with the Lagrangian particle dispersion model FLEXPART-COSMO , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7131, https://doi.org/10.5194/egusphere-egu21-7131, 2021.

Methane is a major greenhouse gas that has increased since the pre-industrial era and reducing its emissions is potentially an effective way of mitigating the radiative forcing in the short term. The oil & gas industry has a positive contribution to the global atmospheric methane budget with fugitive emissions from infrastructure installations such as offshore oil platforms. As part of the United Nations Climate and Clean Air Coalition (UN CCAC) objective to quantify global CH4 emissions from oil and gas facilities, a series of aircraft campaigns have been carried out in the Norwegian sea among other areas. We report on the Lagrangian modelling activity of the emissions and transport sensitivities used to support the flux assessment. Source identification has been carried out based on backward modelling and has proved useful to interpret observations form the in situ airborne platforms. In addition, forward modelling of the emission plume in high resolution has been applied to constraining the plume height for mass balance methods assessment. Dependency of the resulting uncertainty of the flux estimates on various factors such as the choice of the meteorology and the of the Lagrangian model parameters is also discussed.

How to cite: Pisso, I., Foulds, A., and Allen, G.: Modelling of methane emissions from offshore oil platforms in the Norwegian sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16518, https://doi.org/10.5194/egusphere-egu21-16518, 2021.

Svalbard is a near pristine Arctic environment, where long-range transport from mid-latitudes is an important air pollution source. Thus, several previous studies investigated the background nitrogen oxides (NO_x) and tropospheric ozone (O₃) springtime chemistry in the region. However, there are also local anthropogenic emission sources on the archipelago such as coal power plants, ships and snowmobiles, which may significantly alter in situ atmospheric composition.  Measurement results from three independent research projects were combined to identify the effect of emissions from various local sources on the background concentration of NO_x and O₃ in Svalbard. The hourly meteorological and chemical data from the ground-based stations in Adventdalen, Ny-Ålesund and Barentsburg were analysed along with daily radiosonde soundings and weekly data from O₃ sondes. The data from the ERA5 reanalysis were used to evaluate the prevailing synoptic conditions during the fieldwork. Although the correlation between the NO_x concentrations in the three settlements was low due to dominant influence of the local atmospheric circulation, cases with common large-scale meteorological conditions increasing the local pollutant concentration at all sites were identified. In colder and calmer days and days with temperature inversions, the concentrations of NO_x were higher. In contrast to NO_x values, O₃ concentrations in Barentsburg and at the Zeppelin station in Ny-Ålesund correlated strongly, and hence the prevailing synoptic situation and long-range transport of air masses were controlling factors for them. The Lagrangian models HYSPLIT and FLEXPART have been used to investigate air mass transport and transformations during the large scale O₃ depletion and enrichment events. The factors affecting Arctic springtime photochemistry of O₃ have been investigated thoroughly using Lagrangian and Eulerian numerical weather prediction model data and Metop GOME-2 satellite observations.

How to cite: Dekhtyareva, A., Hermanson, M., Nikulina, A., Hermansen, O., Svendby, T., Holmén, K., and Graversen, R.: Springtime nitrogen oxides and tropospheric ozone in Svalbard: local and long-range transported air pollution, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9126, https://doi.org/10.5194/egusphere-egu21-9126, 2021.

Transport of water from an evaporation source towards a precipitation sink is the essence of the atmospheric water cycle. However, there are significant challenges with the representation of the atmospheric water cycle in models. For example, incomplete representation of sub-grid scale processes like evaporation, mixing or precipitation can lead to substantial model errors. Here we investigate the combined use of Lagrangian and Eulerian models and in-situ observations of stable water isotopes to reduce such sources of model error. The atmospheric water cycle in the Nordic Seas during cold air outbreaks (CAOs) is confined to a limited area, and thus may be used as a natural laboratory for hydrometeorological studies. We apply Lagrangian and Eulerian models together with observations taken during the ISLAS2020 field campaign in the Arctic in spring 2020 for characterising source-sink relationships in the water cycle. During the field campaign, we observed an alternating sequence of cold air outbreaks (CAO) and warm air intrusions (WAI) over the key measurement sites of Svalbard and northern Norway. Thereby, meteorological and stable water isotope measurements have been performed at multiple sites both upstream and downstream of the CAOs and WAIs. The Lagrangian model FLEXPART has been run with the input data from the regional convection-permitting numerical weather prediction model AROME Arctic at 2.5 km resolution to investigate transport patterns. The combination of observations and model simulations allows us to quantify the connection between source and sink for different weather systems, as well as the link between large-scale transport and stable water isotopes. Findings will lead to a better understanding of processes in the water cycle and the degree of conservation of isotopic signals during transport. This study may also serve as a guideline on how to evaluate the performance of Lagrangian transport models using stable water isotope measurements, and on how to detect constraints for quantifying the transport route and evaporation source from stable water isotope measurements for future work, including an aircraft campaign planned in 2021.

How to cite: Johannessen, A., Dekhtyareva, A., Seidl, A., and Sodemann, H.: Linking Lagrangian model simulations with stable water isotope measurements in Arctic weather systems., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10984, https://doi.org/10.5194/egusphere-egu21-10984, 2021.

A robust result of climate model simulations is the moistening of the stratosphere.
Many models show their strongest changes in stratospheric water vapor in the extratropical lowermost stratosphere, a change which could have substantial climate feedbacks (e.g. Banerjee et al. 2019). However, models are also heavily wet-biased in this region when compared to observations (Keeble et al. 2020), presenting some uncertainty on the robustness of these model results.

In this study, we investigate the contribution of the choice of model transport scheme to this wet bias using a climate model (EMAC) coupled with two transport schemes: the standard EMAC flux-form semi-Lagrangian (FFSL) scheme and the fully-Lagrangian scheme of CLaMS. This experiment has the advantage of analytical clarity in that the dynamical fields driving both transport schemes are identical. Prior work using this tool has shown large differences in transport timecales within the extratropical lowermost stratosphere depending on the transport scheme used (Charlesworth et al. 2020). 

These results also suggested that EMAC-CLaMS should reduce the transport of water vapor into this region, but calculations of water vapor fields using this tool were not performed until now. We present the results of that work, comparing the water vapor fields calculated using EMAC-CLaMS and EMAC-FFSL online. Two model simulations were performed, wherein each water vapor field was used to drive radiation calculations, such that the radiative consequences of applying one transport scheme or the other could be assessed.

References:

Banerjee, A., Chiodo, G., Previdi, M. et al. Stratospheric water vapor: an important climate feedback. Clim Dyn 53, 1697–1710 (2019). https://doi.org/10.1007/s00382-019-04721-4

Keeble, J., Hassler, B., Banerjee, A., Checa-Garcia, R., Chiodo, G., Davis, S., Eyring, V., Griffiths, P. T., Morgenstern, O., Nowack, P., Zeng, G., Zhang, J., Bodeker, G., Cugnet, D., Danabasoglu, G., Deushi, M., Horowitz, L. W., Li, L., Michou, M., Mills, M. J., Nabat, P., Park, S., and Wu, T.: Evaluating stratospheric ozone and water vapor changes in CMIP6 models from 1850–2100, Atmos. Chem. Phys. Discuss. [preprint], https://doi.org/10.5194/acp-2019-1202, in review, 2020. 

Charlesworth, E. J., Dugstad, A.-K., Fritsch, F., Jöckel, P., and Plöger, F.: Impact of Lagrangian transport on lower-stratospheric transport timescales in a climate model, Atmos. Chem. Phys., 20, 15227–15245, https://doi.org/10.5194/acp-20-15227-2020, 2020. 

How to cite: Charlesworth, E., Plöger, F., and Jöckel, P.: Impact of Lagrangian transport on lower-stratospheric water vapor and radiative balance in a climate model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7571, https://doi.org/10.5194/egusphere-egu21-7571, 2021.