Gravitational settling is a crucial parameter to study the transport and distribution of atmospheric concentrations, sources, and sinks of particles. Although the settling velocity is highly dependent on the particle shape, most atmospheric transport models assume particles to be spherical, ignoring other geometries. In this study, we focus on the gravitational settling of microplastics (MP) particles, which often deviate strongly from sphericity. For instance, MP fibers can be approximated more closely by cylinders rather than spheres. 

Here, we present the results of conducted experiments with extremely elongated MP particles to define their settling velocity. This was done with the settling column and 3D-printed MP particles of different shapes (straight cylinders, half-circled cylinders, and quarter-circled cylinders), lengths, and aspect ratios. The experimental data shows that the parameterization scheme for shape correction proposed by Bagheri and Bonadonna, 2016 is a reliable tool to predict the gravitational settling of fibers considering different types of particle orientation (random, horizontal, and average of both).

This scheme was implemented in the gravitational settling scheme of the Lagrangian transport model FLEXPART to eliminate uncertainties regarding the shape of a particle when simulating solid particle transport. As a study case, the mass concentration and deposition 3D fields of MP fibers were estimated according to the global population density to understand the contribution of the individual sites/regions to MP contamination of the atmosphere, land, and World Ocean.

How to cite: Tatsii, D., Bagheri, G., Bucci, S., Bakels, L., and Stohl, A.: Gravitational settling of microplastic fibers: experimental results and implications for global transport, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13231, https://doi.org/10.5194/egusphere-egu23-13231, 2023.

Introduction: Following their transport, atmospheric pollutants are deposited on the ground, on plants or on water. Depending on the substances involved, ecosystems can be adversely affected by the deposition of nutrients or pollutants. In order to be able to counteract the potential ecological risks through environmental policy measures, it is necessary to measure the atmospheric inputs of potentially harmful substances. For this reason, heavy metal concentrations in mosses used as accumulators of atmospherically deposited substances have been determined since 1990 for every five years at up to 7300 locations in up to 34 European countries. In 2005 nitrogen was added. Persistent organic compounds were determined for the first time in the European Moss Survey in 2010, in Germany firstly in the Moss Survey of 2015/2016. Microplastics were added to this group of substances for the 2020/2021 survey. Here, we are presenting results for microplastic and a variety of persistent organic pollutants (POP) from the 2020/2021 moss survey in Germany. Materials and Methods: Sampling was performed at 20 sites according to the recommendations of the Moss Survey Manual. Afterwards a sample preparation method was established for Thermo-Extraction-Desorption-GC-MS and RAMAN spectroscopy to analyze the microplastic concentration as well as number in the moss samples. Analyses for POPs were performed as described by Dreyer et al. 2018 with slight modifications. Overall, about 120 compounds (PAH, PCDD/F, PCB, PFAS, HBCD, PBB, PBDE, alternative halogenated flame retardants (HFR)) were analysed. Results: In all Moss samples microplastic were detected. The highest concentration in all samples was observed for polyethylene, followed by polyethylene terephthalate, polypropylene and styrene-butadiene and in one sample polystyrene. At the two sampling sites near the sea the highest microplastic concentrations were indicated, whereas no correlation with the other sampling location (urban, agriculture, forest) could be detected. PBB and indicator PCB were not observed above the LOQ in any sample. PFAS and dioxin-like PCBs were very rarely found above the LOQ. In contrast, certain PCDD/F, PAH, HBCD, PBDE and HFR were frequently observed. Current concentrations at sampling sites compared to those of sites that have also been investigated in 2015/2016 were in the same order of magnitude or declined. For HBCD, concentrations declined distinctly by a factor of up to 9. Conclusions: Microplastics and many POPs were observed in moss samples indicating their suitability to monitor atmospheric deposition of these substance groups by this bioindicator. Challenges exist for PBB, PCB or PFAS either because environmental concentrations are too low with respect to the LOQ or the pollutants’ environmental behavior limit accumulation in moss. Within the past five years, most POPs concentrations in moss samples from Germany stayed more or less the same or decreased.

Acknowledgements:

We are thankful to the German Environment Agency (Umweltbundesamt) for funding this study (FKZ 3720632010).

 References:

• UNECE ICP VEGETATION (2020) Heavy metals, nitrogen and POP in European mosses: 2020 survey monitoring manual. https://icpvegetation.ceh.ac.uk/sites/default/files/ICP%20Vegetation%20moss% 20monitoring %20manual %202020.pdf
• Dreyer A, Nickel S, Schröder W. et al. (2018). Environ. Sci. Eur. 30 (43): 1-14.

How to cite: Wolf, C., Wenzel, M., Dreyer, A., Schroeder, W., Nickel, S., Voelksen, B., Kube, C., and Tuerk, J.: Microplastics and Persistent organic pollutants in moss samples from Germany, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2660, https://doi.org/10.5194/egusphere-egu23-2660, 2023.

An increasing body of evidence documents measurable levels of a broad range of PFAS compounds in precipitation - which translate into substantial deposition loads to terrestrial and aquatic resources. In many environments these atmospheric deposition fluxes can represent the dominant source of PFAS – however, very large gaps in our understanding of atmospheric sources and processing, and deposition fluxes of PFAS remain. 

To address these issues the University of Wisconsin-Madison Wisconsin State Laboratory of Hygiene (WSLH) and the WSLH managed National Atmospheric Deposition Program (NADP), initiated a program to evaluate the efficacy of the US NADP National Trends Network (NTN) for assessment of wet-deposition of PFAS and provide novel new data on levels of PFAS in precipitation across the US.  Dedicated experiments with a diverse suite of 34 PFAS compounds addressed system blanks and stability of the PFAS species in the NTN precipitation collectors. A robust standardized protocol was promulgated for PFAS wet-deposition measurements using the NADP-NTN infrastructure and analytical tools at the WSLH.

We have now applied this protocol in several studies, including in an intensive 5-month study in 2020 at NTN sites across Wisconsin, USA (Pfotenhauer et al., 2022), and in an on-going large-scale nationwide monitoring effort at 10 NTN sites initiated in 2020 and supported by the US Environmental Protection Agency-Office of Research & Development (EPA-ORD).  In the Wisconsin study, 91 precipitation samples, along with an array of QA/QC samples were collected from 8 NTN sites across Wisconsin, and analyzed for 34 PFAS compounds. Concentrations of individual PFAS compounds were generally less than 1 ng/L, however, summed PFAS concentrations ranged from 0.7 to 6.1 ng/L with a median of 1.5 ng/L. Perfluoro carboxylates (PFCAs) were detected most frequently and constituted an average of 83% of the total PFAS mass. Daily flux values ranged from 1.3 to 47.4 ng/m²/day with a median of 5.7 ng/m²/day. Differences in the PFAS fingerprints were observed among the 8 sampling sites, reflecting local sources.

How to cite: Shafer, M. and Gay, D.: Per- and Polyfluoroalkyl Substances (PFAS): Concentrations and Deposition in Precipitation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10074, https://doi.org/10.5194/egusphere-egu23-10074, 2023.

The bushfires in Australia during the 2019/2020 season were particularly severe, leading to the creation of a plume of smoke that rose into the Lower Stratosphere and resulted in record levels of smoke concentration.  In early January 2020, the plume disperses into independent transport paths in the stratosphere. Following a Lagrangian approach, we study the three dimensional atmospheric transport in the region at this time to better understand the cause of the splitting, the subsequent transport geometry, and the influence of the plume buoyancy on its movement. Aided by the Finite Time Lyapunov Exponent tool, we identify Lagrangian Coherent Structures (LCS) which simplify the three-dimensional transport description and make possible the characterization of the smoke plume evolution. 

Our numerical modeling results were able to replicate the observed behavior of the smoke plume during the bushfires in Australia, including the splitting of the plume into multiple pathways. In the model, we found parcels trajectories with the same behavior as the observed plume, highlighted the contribution of the passive advection of the plume by the wind versus the buoyancy effect of hot smoke, delineated the plume into regions destined to different fates, and showed that the division of the main path was affected by an eddy.

How to cite: Curbelo, J. and Rypina, I. I.: Lagrangian atmospheric transport of the smoke plume from the large Australian Wildfire Event of 2019/2020., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9344, https://doi.org/10.5194/egusphere-egu23-9344, 2023.

Air pollution contributes to increased mortality and lower quality of life. It imposes additional distress on people suffering from respiratory diseases such as pollinosis. A quarter of the adult population and a third of all children in Europe are estimated to suffer from airborne allergenic pollen. In the future even more people might be subjected to pollen allergies since changes in climate and land-use tend to increase the amount of allergenic airborne pollen and prolong the pollen seasons. Good pollen mitigation measures may ease the symptoms but it requires proper knowledge on the modelling and forecasting of allergenic pollen in the air.

We start from the setup of the pollen transport model SILAM (System for Integrated modeLling of Atmospheric coMposition), driven by ECMWF ERA5 meteorology in a bottom-up emission approach for the period 1982-2019 for the Belgian territory. The dynamic vegetation component in the pollen transport model is determined by pollen emission source maps which have to be ingested in the model for every pollen season. The used maps are derived by merging multi-decadal datasets of spaceborne NDVI with forest inventory data in a Random Forest statistical framework.

Here we study the impact of spatially-varying pollen emission sources on the modelled airborne birch pollen levels compared with in-situ observations in a Monte-Carlo approach. Preliminary analysis indicates that by selecting the model scenario corresponding with median pollen levels, the correlation between the modelled and observed pollen levels increases with 16%. We show the importance of ingesting the appropriate pollen emission source map when the modelling and forecasting of airborne birch pollen levels is aimed for. Finally, we review methods to relate the pre-pollen season meteorology or vegetation state on the birch pollen loads of the up-coming season as tool for selecting the best emission source map in the forecasting framework.

How to cite: Verstraeten, W. W., Bruffaerts, N., Kouznetsov, R., Sofiev, M., and Delcloo, A.: Mediating Airborne Birch Modelling and Forecasting, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3607, https://doi.org/10.5194/egusphere-egu23-3607, 2023.

The cosmogenic radionuclides ⁷Be and ¹⁰Be are useful aerosol tracers for atmospheric transport studies. Combining ⁷Be and ¹⁰Be measurements with an atmospheric transport model, not only can improve our understanding of the radionuclide transport and deposition processes, but also can provide an evaluation of the transport process in the model. To simulate those aerosol tracers, it is critical to evaluate the influence of production uncertainties in simulations. Here we use the GEOS-Chem transport model to simulate ⁷Be and ¹⁰Be with different production scenarios: the default production scenario in GEOS-Chem based on an empirical approach, and two production scenarios from the CRAC: Be (Cosmic Ray Atmospheric Cascade: application to Beryllium) model. The model results are comprehensively evaluated with a large number of measurements including more than 490 sites for surface air concentrations and 300 sites for deposition flux. The model can reproduce the absolute values and temporal variability of ⁷Be and ¹⁰Be surface concentrations and deposition fluxes on annual and sub-annual scales. The simulations using the CRAC production scenarios yield a better agreement with the measured deposition flux (70% of data within a factor of 2) compared to the default production scenario in the GEOS-Chem model (59%).  This better agreement is also observed for the vertical profiles of air ⁷Be concentrations.  Independent of the production models, surface air concentrations and deposition fluxes from all simulations show similar seasonal variations, suggesting a dominant meteorological influence. Finally, we demonstrate the importance of including time-varying solar modulation in the production calculation, which can significantly improve the agreement between the model and measurements, especially from mid to high latitudes.

How to cite: Zheng, M., Liu, H., Adolphi, F., Muscheler, R., Lu, Z., Wu, M., and Prisle, N.: Evaluation of GEOS-Chem model performance for simulating transport and deposition of cosmogenic 10Be and 7Be using different production models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11485, https://doi.org/10.5194/egusphere-egu23-11485, 2023.

Chlorine 36 (³⁶Cl, T_1/2 = 301,000 years) is a radionuclide with natural and anthropogenic origin that can be rejected during decommissioning of nuclear power plants or chronically during recycling of used nuclear fuels. Once emitted into the atmosphere, chlorine 36 (gas and particles) can be transferred to the soil and vegetation cover by dry and wet deposition. However, quantitative constraints of these deposits are very scarce. Because of its relatively high mobility in the geosphere and its high bioavailability, chlorine 36 fate in the environment should be studied for environmental and human impact assessments.
The aim of this study is therefore to develop dry depositional models for the gaseous and particulate fractions of chlorine 36. The model used for the parameterization of gaseous chlorine 36 dry deposition on grass is the << Big-leaf >> model based on the electrical analogy (Seinfield 1985). It was adapted from the Bah (2020) model developed for iodine. For particulate chlorine 36, the Damay-Pellerin (2017) model was used. This model requiring the diameter of particulate chlorine 36 to be known, a sample of aerosol was taken in the chlorine 36 plume to determine on which particle size it is fixed. The sampling was performed on a low pressure impinger (LPI, DEKATI) of 13 levels for particles with diameters between 30nm and 10μm. In order to obtain model input data, meteorological and micrometeorological parameters were measured continuously at the IRSN La-Hague technical platform (PTILH, France). The PTILH is located 2 km north of Orano La-Hague plant which emits small quantities of chlorine 36. An ultrasonic anemometer (Young 81000V) installed at a height of 4,5 m from the ground measured the direction (°), the velocity u (m/s) and the air friction velocity u* (m/s), the sensible heat flux H, the Monin-Obukhov length (L) and the atmospheric stability (1/L). A weather station (Spectrum Watchdog, series 2000) measured temperature Ts (°C), relative humidity RH (%), dew point (°C), global radiation SR (Wat/m2) and photosynthetic active radiation PAR (μM/m².s). Sampling campaigns of 2 weeks were also conducted at the PTILH site to determine experimental depositional rates of chlorine 36. Chlorine 36 measurements were carried out by acceleration mass spectrometry at CEREGE-LN2C (France).
The particle size distribution of the aerosol sample from chlorine 36 plume shows two peaks, a main one at 2μm and a second one at 10μm, typical distribution of marine aerosol. The models yield chlorine 36 depositional velocities between 6,7.10^-3 and 10^-2 m/s for the particulate fraction, and between 5.10^-3 and 1,3.10^-2 m/s for the gaseous one. The total dry depositional velocities (particles and gas) calculated from the model are less than one order of magnitude than the ones obtained experimentally.

How to cite: Sourabie, D.-G., Hebert, D., Benedetti, L., Vitorge, E., Lourino-Cabana, B., Guillou, V., and Maro, D.: Modelling the atmospheric chlorine 36 dry deposition on grass using micrometeorology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17115, https://doi.org/10.5194/egusphere-egu23-17115, 2023.

Rime is an under-researched pathway of the atmospheric deposition of ecological and environmental relevance, in particular in mountain regions. Rime alongside with snow were sampled and assessed for S-SO₄^2- and N-NO₃^- at ten border mountaintop sites across the Czech Republic (CR) in the three consecutive winters of 2009–2011. Our observations indicated significantly higher sulphur (S) and nitrogen (N) contents in rime as compared to snow at all sites.  Whereas the highest S contamination was found in the industrial North, the highest N contamination was found unexpectedly in the relatively unpolluted South. The measurements were put in context with data driven geo-spatial modeling results (Hůnová et al., 2016) of annual wet vertical (rain and snow) and horizontal (fog and rime) deposition. Despite relatively low hydrological input of rime, it contributed significantly to annual atmospheric deposition. At nine out of ten sites, the winter-time deposition of S via rime corresponded to 5–13% of annual wet-only S deposition, while it reached full 25% at the most S-polluted TET site in the Orlicke hory Mts., a region bordering Poland (Hůnová et al., 2022). Modelled results showed that mean winter rime deposition corresponded to about 6–25%, and mean winter snow deposition made up 25–72.5% of mean annual N-NO₃^- wet-only deposition (Hůnová et al., submitted). Model N-NO₃^-occult deposition estimated from throughfall and total (wet and dry) deposition is highly uncertain, however: N throughfall is not a relevant proxy for estimation of realistic total N deposition due to N exchange between the tree canopy and atmosphere.  Considering the fact that wet-only deposition is a year-long phenomenon, whereas rime forms under the climatological conditions of the Czech middle elevated mountains during only a few (2–3) months a year, we can conclude that the rime deposition pathway should not be neglected in quantifying the real atmospheric deposition flux in mountain regions as it might contribute to the real deposition flux substantially even in mountains of medium elevation, as was observed in the CR.

References:

Hůnová I., Kurfürst P., Vlček O., Stráník V., Stoklasová P., Schovánková J., Srbová D., 2016. Towards a Better Spatial Quantification of Nitrogen Deposition: A Case Study for Czech Forests. Environmental Pollution 213, 1028–1041. doi: 10.1016/j.envpol.2016.01.061.

Hůnová I., Novák M., Kurfürst P., et al., 2022. Contribution of rime to atmospheric sulphur deposition in Central Europe: A combined empirical and modelling approach. Atmospheric Environment 270, 118877. https://doi.org/10.1016/j.atmosenv.2021.118877.

Hůnová I., Novák M., Kurfürst P., et al., submitted. Comparison of vertical and horizontal atmospheric deposition of nitrate at Central European mountain-top sites during three consecutive winters.

How to cite: Hunova, I., Novak, M., Kurfürst, P., Skachova, H., Stepanova, M., Komarek, A., Curik, J., Veselovsky, F., Prechova, E., and Bohdalkova, L.: Rime – a non-negligible pathway of sulphur and nitrogen atmospheric deposition in middle-elevated Central European mountains  , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3129, https://doi.org/10.5194/egusphere-egu23-3129, 2023.

Eutrophication is one of the main reasons threatening biodiversity in Germany. To quantify the risk for biodiversity caused through nitrogen deposition, in Germany national data on the exceedance of critical loads for eutrophication are used as indicators for the National Strategy on Biodiversity and for the National Sustainability Development Strategy. In addition, to prevent ecosystems from unwanted further excessive nitrogen deposition, according to the German emission control and nature protection legislation, nitrogen deposition has to be assessed when new nitrogen emitting projects are submitted. To support the development of the national nitrogen strategy and devise regional emission targets an effort was made to provide insight into the geographic regions of origin of the nitrogen deposited within the federal states in Germany.

The atmospheric dispersion modelling was performed with chemistry transport model LOTOS-EUROS. Simulations over Germany were run with a resolution of 0.10° longitude by 0.05° latitude, nested in a European simulation. In addition to species concentrations and deposition fluxes, the contributions of predefined source categories were calculated and tracked using a labelling approach for the year 2019. The labels applied in this simulation encompass all emissions from the 16 individual German federal states, all 9 neighbouring countries of Germany and countries further away. Additionally, labels were attached to international shipping emissions, natural emissions, and boundary conditions to cover intercontinental transport. This result in a full source-receptor matrix with contributions to N-deposition in all federal states with contributions from all states and neighbouring countries. To assess contributions of local sources, an additional simulation was performed with emission reductions on three surface and two stack point sources.

Largest average depositions in Germany are found in Hamburg and Bremen followed by Niedersachsen, Nordrhein-Westfalen and Schleswig-Holstein. Hamburg and Bremen are small city states with relative high NOx emission densities. However, local emissions only contribute approximately 20%, main contributors are neighbouring areas Niedersachsen and Schleswig-Holstein due to their large agricultural sector with high ammonia emissions. A general trend can be spotted that states with dominant NHx emissions also have the highest local deposition. This holds for Baden-Württemberg, Bayern, Niedersachsen, Nordrhein-Westfalen and Schleswig-Holstein, where on average 40% of the nitrogen deposition originates from the sources within each state. For many states, there is also a considerable contribution of countries surrounding Germany. Emissions from the Netherlands contribute mainly in Bremen, Hamburg, Niedersachsen, Nordrhein-Westfalen and Schleswig-Holstein. The other main contributor is France, affecting mainly the states in southern Germany. The assessment of local contributions from the surface point sources shows that about 18-22 % of the emitted mass is deposited within a radius of 20 km from the source In contrast, for two the stack point sources, NHx deposition within 20 km of the source is only about 5% of the emission strength.

How to cite: Kranenburg, R., Schaap, M., Geupel, M., Feigenspan, S., and Moravek, A.: Origin of nitrogen deposition in Germany: Source allocation and influence of local emissions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15811, https://doi.org/10.5194/egusphere-egu23-15811, 2023.

Recent studies show that effective pollution control strategies have led to a significant reduction in air pollution in Cyprus. However, the same studies attributed a large number of pollution episodes to the long-range transport of pollutants from regional sources. Black carbon (BC) and carbon monoxide (CO), with a lifetime of several weeks to several months in the troposphere, are considered reliable aerosol and gaseous pollutants to quantify the contribution of regional sources. This study aims to investigate the contribution of anthropogenic sources to atmospheric pollutants over the Eastern Mediterranean. Using FLEXPART, a Lagrangian dispersion model, the origin and residence time of air masses over Cyprus from Europe and the MENA region have been simulated with a temporal resolution of 3 hours for each day of 2019. Then, by coupling FLEXPART simulations to global emission inventories, including MACCity and CAMS-GLOB, the contribution of sources to CO and BC simulations in Cyprus was determined separately for each sector and country in the study area. Results show that CO concentrations are mainly modulated by sources in Turkey. Secondary sources are found in MENA (Iran, Iraq, and Syria) in the cold period of the year and in Eastern (Ukraine and Russia) and Western Europe (Germany and Italy) in the warm seasons. While CAMS-GLOB simulations identify the main sources in agricultural (in the cold period) and residential (in the warm period) sectors, traffic sources have also been identified with the largest contributions in MACCity simulations. Regarding BC simulations, most sources are found in Turkey in the agricultural (in CAMS-GLOB simulations) and industrial (in MACCity simulations) sectors. Local sources were found influential only in the MACCity BC simulations. This can be attributed to uncertainties in the emission inventories and in the simulations of atmospheric residence times. Our results can inform policy- and decision-makers in implementing efficient abatement strategies, improving air quality, and reducing human exposure.

How to cite: nabavi, S. O. and Christoudias, T.: Long-range source apportionment of black carbon and carbon monoxide over Cyprus using FLEXPART and global emission inventories, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16207, https://doi.org/10.5194/egusphere-egu23-16207, 2023.