Within the Copernicus Atmosphere Monitoring Service (CAMS), ECMWF operates the Integrated Forecasting System with atmospheric composition extension (IFS-COMPO) to provide global forecasts and reanalyses of aerosols and trace gases. In support of ongoing preparations for a new CAMS reanalysis, which will cover the years 2003-present, multi-decadal model simulations with a fixed IFS-COMPO model configuration, but excluding composition data assimilation, have been produced for the same period. Recently these simulations have been extended into the past, back to 1978, with the aim to produce a consistent assessment of trends in atmospheric composition-related aspects. This includes an analysis of model trends in tropospheric and stratospheric ozone, aerosol optical depth, and nitrogen and sulfur deposition, and methane lifetime.  For this purpose we apply a version of CMIP emissions for years prior to 2003, when no CAMS-GLOB emissions are available, along with appropriate surface nudging of CFC’s, nitrous oxide and methane. We run multiple batches of multi-year simulations in parallel, driven by ERA5 meteorology. We take care of a reasonable hand-shake procedure for the different emission estimates as they cross for the year 2003.

In this contribution we report on the design and first assessment of global atmospheric composition trends for the period 1978-2024 in these model simulations, and discuss evaluation results with emphasis for the 2003-2020 period, focusing on trends in simulated methane loss rate, and factors which drive these results.

How to cite: Huijnen, V., Checa-Garcia, R., Rémy, S., Senan, R., Metzger, S., Chabrillat, S., and Flemming, J.: A 45-year chemistry and aerosol simulation with IFS-COMPO: trend analysis and first evaluation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9901, https://doi.org/10.5194/egusphere-egu25-9901, 2025.

Black carbon (BC) is a significant climate forcer and a major health hazard especially close to its sources. BC has both natural (e.g., wildfires) and anthropogenic sources (e.g., industry, traffic, oil and gas industries). Its distribution in the atmosphere is highly inhomogeneous. Understanding both the spatial distribution and the magnitude of BC emissions is critical for accurate climate modeling. However, emission inventories for BC are fraught with uncertainties, largely stemming from uncertainties in emission factors, which complicate global scale modeling efforts. Observational data, especially when obtained by different measurement techniques, which is essential for constraining emission estimates, carry their own uncertainties.

In this study, we present a global inversion of BC emissions over a 5-year period, using a combination of global observations, atmospheric modeling with FLEXPART, and a Bayesian inversion algorithm (FLEXINVERT). Our approach aims to reconcile uncertainties in both emissions and observations, providing a more robust estimate of BC distribution and sources. Even though presenting a global picture, we focus on Europe, an area with a high density of observation sites, enabling more precise emission estimates. The tropics and southern hemisphere have only sparse observations. Moreover, we highlight the significant role of wildfires as a source of BC, with implications for both local and global climate impacts.

Our findings contribute to improving the accuracy of BC inventories which can be used both for climate modelling and air quality assessments.

How to cite: Eckhardt, S., Thompson, R. L., Evangeliou, N., Pisso, I., Yttri, K.-E., Groot Zwaaftink, C., and Platt, S. M.: Global Inversion of a Black Carbon Emissions based on FLEXPART modelling and a Bayesian inversion algorithm, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11621, https://doi.org/10.5194/egusphere-egu25-11621, 2025.

Aerosol components have distinct health and climate impacts, hence considering them is essential to reduce uncertainty in estimating the health impacts attributed to aerosol. Organic aerosols (OAs) are one of the significant components of aerosol having a substantial share in total aerosol mass in Europe with significant seasonal and spatial variations. OAs are majorly emitted from fossil fuel combustion and generated through secondary aerosol formation too and based on the origin OA components can be categorized into biomass-burning organic aerosol (BBOA), hydrocarbon-like aerosol (HOA), and oxygenated organic aerosol (OOA).  OA measurements are limited, and measurements of its components are even more sparse due to the need for highly sophisticated instruments and advanced technical expertise. Additionally, OA and its components are not mandated for monitoring at all sites under government regulations, they are measured only at spatially sparse supersites. Chemical transport modeling provides spatially and temporally continuous OA and OA components with some vested uncertainty, but they are generally done at coarser resolution because of computational constraints. Whereas epidemiologist requires data at a finer resolution to link them with the local scale health data. Hence we are modeling total OA and OA components (BBOA, HOA, and OOA) at a fine resolution over Europe. Here, we use an integrated modeling approach combining a chemical transport model and machine learning algorithms. We simulated OA and its components using a comprehensive air quality model with extensions (CAMx) at around 10 km resolution over Europe for 10 years. In the subsequent step, a random forest (RF) model was trained using CAMx outputs, meteorological parameters, and land use variables as predictors to estimate observed aerosol component concentrations as the target to improve the predictions and enable downscaling of the outcome. Here we used an unparallel large OA and OA components observation inventory made with measurements from various research and operational groups across the world, consisting of 50,000 daily observations for OA and 15,000 daily observations for OA components from 140 and 40 locations respectively. This approach improves predictions with an increase in r2 to 0.43 from 0.31 for total OA and reduces the RMSE from  1.5, 0.8, 3.1 µg/m³ to 0.3, 0.2 and 0.45 µg/m³ for BBOA, HOA, and OOA respectively, while also enabling downscaling. This provided us with OA and OA components at a higher resolution of 200m across Europe for 10 years. The high-resolution modeled map illustrates the regional to local spatial distribution of OA and its components. Such high-resolution aerosol component modeling is instrumental for epidemiological studies when combined with local health datasets. Local-scale analysis with such datasets helps identify dominant aerosol components and their sources.

How to cite: Upadhyay, A., El Haddad, I., and collaborators, A. P.: High-resolution modeling of organic aerosol and its components over Europe, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17517, https://doi.org/10.5194/egusphere-egu25-17517, 2025.

Trends in daily PM_2.5 mass concentrations were assessed at 5 rural background sites in France over the period 2014-2021, together with major particulate components associated with (i) anthropogenic emissions including fossil fuels (FF) and biomass burning (BB) from primary emissions; and (ii) non-sea-salt sulphate, nitrate and ammonium, i.e., secondary particulate constituents from gaseous precursors sulphur dioxide, nitrogen oxides and ammonia, respectively. To disentangle the influence of weather, long-range transport, and the oxidative capacity of the atmosphere, boosted regression tree (BRT) models were built at each site; and normalised time series were calculated by randomising the value of the explanatory variables at a given time. Different BRT models were formulated and two types of normalised PM_2.5 time series were calculated: de-weathered time series (without the influence of the meteorological and long-range transport) and de-weathered & de-oxidised time series (randomisation of meteorology, transport and O_X (NO₂ + O₃) levels). Over the studied period, PM_2.5 concentrations decreased at approximatively -5% year^-1, almost 1.5 times faster than changes in primary emissions in France. Overall trends in de-weathered, and de-weathered and de-oxidised PM_2.5 concentrations were lower than trends in PM_2.5 observations for the same period, at -3.9% year^-1 and -3.2 % year^-1, respectively. Trends in de-weathered & de-oxidised PM_2.5 were close to those in emissions, demonstrating the importance of including variables capturing the oxidative capacity of the atmosphere in the normalising techniques to compare trends in PM_2.5 with trends in primary emissions. Trends in observations of PM_2.5 were consistent with trends in nitrate particles from reduced NO_X emissions, and to trends in ammonium particles and biomass burning.

How to cite: Font, A., F. de Brito, J., Riffault, V., Conil, S., Jaffrezo, J.-L., and Bourin, A.: Do rural background sites capture changes in primary PM2.5 emissions at the national scale? Recent trends in PM2.5 and its main components in metropolitan France., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10935, https://doi.org/10.5194/egusphere-egu25-10935, 2025.

Recent successes in reducing PM_2.5 concentrations in the atmosphere have led to significant shifts in the concentrations of various compounds. Sustaining the efficacy of control measures requires continuous monitoring of these changes. This study examined the decadal variations from 2012 to 2022 of concentrations of PM_2.5 and its inorganic components—sulfate, nitrate, ammonium, chloride, and non-volatile cations (NVC)—assessed via offline filters at an urban site (Yuen Long, YL) and a suburban site (HKUST, UST) in Hong Kong. We also cross-referenced the offline filter data with online MARGA results at both sites over a portion of the ten-year period for data validation. Our analysis indicates a consistent decline in PM_2.5 concentrations, registering an average reduction of 1.55 ± 0.16 μg/m³ (p < 0.01) per year in YL and 1.37 ± 0.17 μg/m³ (p < 0.01) per year in UST during the ten-year period. Inorganic compounds constituted 47.4 ± 10.1% and 51.5 ± 10.0% of PM_2.5 by mass in YL and UST, respectively, with sulfate accounting for over half of PM_2.5 at both sites. The decline in inorganic compounds over the years was primarily attributed to sulfate, which decreased at rates of 0.63 ± 0.04 μg/m³ (p < 0.01) per year in YL and 0.67 ± 0.05 μg/m³ (p < 0.01) per year in UST. While nitrate remained relatively steady in its concentrations, it constituted a larger mass fraction of both inorganic compounds and PM_2.5 at both sites. Seasonal variations were explored by comparing summer and winter trends. The rate of sulfate reduction in winter was approximately twice that in summer at both sites, contributing to ~40% of PM_2.5 reduction, as sulfate and PM_2.5 concentrations were significantly higher in winter. In contrast, nitrate concentrations exhibited an upward trend during winter, with notable increases from 1.87 μg/m³ to 7.63 μg/m³ in YL and from 0.75 μg/m³ to 3.47 μg/m³ in UST between 2020 and 2021, elevating its mass fraction in PM_2.5. In comparison, summer nitrate concentrations averaged below 1 μg/m³.

Our data validation indicated that offline filter-based nitrate measurements were underestimated under high-temperature conditions, casting high uncertainty on summer filter measurements. MARGA data revealed nitrate mass fractions as high as 28% in suburban UST in 2021, significantly greater than the 13% estimated from filter data due to this underestimation. This study highlights the escalating significance of nitrate alongside successful sulfate reductions in the PM_2.5 composition of both urban and suburban areas of Hong Kong, particularly during winter. Future air quality improvement policies should prioritize addressing nitrate. Furthermore, caution is warranted when interpreting nitrate concentrations measured by filters under high-temperature conditions due to the associated measurement uncertainty.

How to cite: Zhang, Z. and Yu, J.: Ten-year trend of PM2.5 sulfate, nitrate, and other inorganic constituents from 2012 to 2021 in urban and suburban sites of Hong Kong, China, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9750, https://doi.org/10.5194/egusphere-egu25-9750, 2025.

The study investigates the spatial and altitudinal variability of aerosol components, including Black Carbon (BC), PM1, PM2.5, PM10, Total Suspended Particles (TSPM), respirable, thoracic, and inhalable particulate matter, across different sites in Gangtok, Sikkim Himalaya. The monitoring locations - Residential (Site 1, 900 m), Commercial (Site 2, 1800 m), and Control (Site 3, 2200 m) demonstrate distinct altitudinal gradients in ambient aerosol concentrations. The measurements were conducted during the winter of 2024 using an Aethalometer AE-33 to measure BC and an EDM 264 to analyse various size of aerosols in the ambient atmosphere. BC associated with PM2.5 decrease from 4.94 µg/m³ at Site 1 to 2.62 µg/m³ at Site 2 and 1.49 µg/m³ at Site 3, while PM2.5 concentrations follow a similar pattern, declining from 84.88 µg/m³ to 18.62 µg/m³. Comparable trends are observed for PM1, PM10, and TSPM, with higher concentrations at lower altitudes indicating the dominance of anthropogenic activities and population density. These components also exhibited strong diurnal variability, with daytime levels consistently higher than night-time levels across all sites. For instance, at Site 1, the mean daytime BC concentration is 5.59 µg/m³, compared to 3.63 µg/m³ at night. This variation is attributed to increased vehicular emissions and other human activities during the day. Additionally, a strong correlation is observed between BC and PM_2.5 levels indicating common sources such as combustion-related activities. Lower temperatures and higher RH at each site, enhanced aerosol condensation and particle deposition, resulting in reduced pollutant concentrations. Components like respirable, thoracic, and inhalable particulates, critical for assessing health impacts, also show decreasing trends with altitude but remain concerning in residential areas at lower altitudes due to their ability to penetrate the respiratory system. BC's role as a short-lived climate pollutant with high radiative forcing potential further emphasizes its environmental significance in the ecologically sensitive Himalayan region. Addressing the sources of aerosols, particularly in densely populated lower-altitude areas, is vital for improving air quality and mitigating health and climate impacts in the Sikkim Himalaya.

How to cite: Ranjan, R. K., Gupta, A., Rajak, R., Baruah, B., Roy, A., Dutta, S., and Prakash, A.: Air Quality Challenges in Gangtok, Sikkim Himalaya: A Study of Aerosol Variability and Impacts, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15915, https://doi.org/10.5194/egusphere-egu25-15915, 2025.

The Global Atmosphere Watch (GAW) Programme of the World Meteorological Organization coordinates a worldwide network of hundreds of ground-based in-situ monitoring stations that provide reliable scientific data on the chemical composition of the atmosphere. Within the framework of the GAW Programme, the Quality Assurance/Scientific Activity Centre Switzerland has developed a web app (GAW-QC, available at www.empa.ch/gaw, see also Brugnara et al., 2024) to support station operators in timely detecting issues in their in-situ measurements of various trace gases.

GAW-QC consists of a dashboard that highlights anomalous values using a mixture of purely data-driven and hybrid anomaly detection techniques. It exploits historical measurements made at the target station as well as the archive of gridded numerical forecasts by the Copernicus Atmosphere Monitoring Service (CAMS). The accuracy of the latter for the specific site is improved through machine learning using multiple predictors, including meteorological parameters and aerosol concentrations.

The app allows station operators to upload their latest measurements, visualize the data with different temporal aggregations, and detect anomalous values using just their internet browser. By combining the information gathered from the dashboard with logbook entries and local expertise, they can effectively flag problematic measurements and even detect instrumental issues that would remain unnoticed otherwise. First case studies indicate that this process can indeed facilitate the detection of malfunctions in the analytical setup and reduce the ingestion of erroneous data into international data repositories. Moreover, it has the potential to shorten data gaps if applied timely.

GAW-QC is publicly available and can be used to analyze historical time series of carbon dioxide, carbon monoxide, methane, and ozone made at 98 GAW stations worldwide. The applicability to a given station depends on whether historical data have been submitted to the GAW world data centers by the station operator. Additional gas species may be added in the future depending on user feedback.

Brugnara, Y., Steinbacher, M., Baffelli, S., and Emmenegger, L.: Technical note: An interactive dashboard to facilitate quality control of in-situ atmospheric composition measurements, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2024-3556, 2024.

How to cite: Brugnara, Y., Baffelli, S., Steinbacher, M., Zellweger, C., and Emmenegger, L.: The GAW-QC App: Improving Quality Control through Data Science and Numerical Forecasts, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10421, https://doi.org/10.5194/egusphere-egu25-10421, 2025.

For nearly 30 years, Empa has operated the World Calibration Centre for Carbon Monoxide, Methane, Carbon Dioxide and Surface Ozone (WCC-Empa) as a Swiss contribution to the Global Atmosphere Watch (GAW) programme. In this capacity, WCC-Empa has played a central role in sustaining and improving the data quality and availability required for climate and environmental research.

A core activity of WCC-Empa is the quality control of GAW stations through on-site system- and performance audits. We have conducted more than 120 audits as an independent verification of the traceability of measurements to the accepted standards of the WMO/GAW programme, which are hosted and distributed by Central Calibration Laboratories (CCLs). These audits also include operator training and capacity building to improve data availability and quality, especially in less developed regions.

Our presentation will focus on the evolution of surface ozone data quality over the past three decades. We have assessed the stability of the traceability chain from the primary reference standard (the NIST Standard Reference Photometer family) to the transfer standards and the analysers used in the field. Unlike other parameters, the technique for measuring ozone has not changed in the last 30 years, and most surface ozone measurements are made using the UV absorption technique. About two-thirds of the comparisons met the data quality objectives (maximum bias of 1 nmol mol^-1) of the GAW programme.

Looking ahead, a new ozone absorption cross-section will be implemented in 2025 (bipm.org/en/ozone). This will improve the accuracy of ozone measurements but will have an impact on exceedances of air quality standards by increasing ozone values by 1.29%. We will discuss the implications of the new cross-section value and provide guidance on how to make the transition.

How to cite: Zellweger, C., Steinbacher, M., and Emmenegger, L.: The Evolution of Surface Ozone Data Quality over the Past 3 Decades, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15590, https://doi.org/10.5194/egusphere-egu25-15590, 2025.

Understanding long-term changes in surface ozone pollution across South Asia, particularly remote region, remains a critical challenge due to the scarcity of surface-based observations. Tropospheric ozone is secondary pollutant and a greenhouse gas whose higher levels pose a serious hazard to human health, crop yield, environment, and climate. In view of this, continuous surface ozone observations was initiated in October 2006 at a high-altitude site Nainital (29.25°N, 79.45°E, 1948 m amsl) in the central Himalayas. This study examines the long-term trends of surface ozone (2007–2022) at this site using ground observations, WRF-Chem model simulation, and reanalysis datasets. The long term trend analysis is done using statistical method adopted by TOAR II  which revealed a negative trend in surface ozone during 2007–2022. However, a negative trend ( about -0.5 ppbv/year) was observed from 2007-2015, and a positive trend (1.2 ppbv/year) from 2016-2022. Investigating different percentiles for such trend highlights that some specific percentiles play a pivotal role in shaping the trend rather than a uniform distribution around the mean or median. Daily peak-to-peak ozone amplitude shows positive trend, with spring exhibiting the steepest rise and autumn the least. While the annual MDA8 ozone exceedance (>50 ppbv) suggests a slight negative trend over the study period with 2022 recorded the highest exceedance. The ERA5 reanalysis ozone shows a negative trend during 2007-2015 and positive trend during 2016-2022 for the nearest pressure levels which is similar tendency as in observed surface ozone. While trend from MERRA-2, CAMS, and AIRS data showed different tendencies. Tropospheric column ozone trends from OMI/MLS indicate a modest positive trend (about 0.2 DU/year) during 2007–2020. WRF-Chem model simulation is able to produce the diurnal and seasonal variation of ozone with some overestimation. Notably, long-term trends diverge, with WRF-Chem model simulations showing positive trend while observations indicate a negative trend. An investigation into meteorological parameters provided no definitive explanation for the shift in trends across the two periods. The trend observed during 2016–2022 over the central Himalayan region underscores the need for a well-defined action plan to mitigate emissions of ozone precursor gases.

How to cite: Tomar, V., Naja, M., Kumar, R., Rawat, P., and Kumar, U.: Decadal Shifts in Surface Ozone Trends at a Central Himalayan Site: Revealing Contrasting Phases from 2007 to 2022., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-857, https://doi.org/10.5194/egusphere-egu25-857, 2025.

Background ozone is highlighted as a factor that reflects the impact of intercontinental transport and international emissions of precursors as well as regional photochemical pollution. In this study, we used daily mean, MDA8 (max. daily 8-hour average), and MinDA8 (min. daily 8-hour average) ozone concentrations obtained from three national background air pollution monitoring stations—Jeju, Ulleung, and Baengnyeong—to investigate the long-term trends of Korea's background ozone concentrations. Ensemble Empirical Mode Decomposition (EEMD) was applied to decompose ozone time series of these concentrations into long-term, medium-termeasonal, and short-term variability for 2001 – 2022. Here, we define the background ozone variations as the long-term component extracted from the daily mean time series to compare them with those estimated in the west coast of the United States and Europe in the previous study.

The results showed that Jeju's background ozone concentration has steadily increased at the rate of 0.26 ppb per year since 2001 similar to those observed in urban monitoring stations, whereas both Ulleung and Baengnyeong stations initially showed increasing trends but shifted to declining trends after 2015, with annual rates of -0.37 and -0.25 ppb per year, respectively. To explore these differences, we defined daily ozone production (DOP) as the difference between MDA8 and MinDA8. The long-term components of DOP in urban stations, extracted using EEMD, was approximately 10 ppb higher than at background stations due to precursor emissions from anthropogenic sources, with little variation over time. In contrast, background DOP has steadily decreased since 2015, with decreasing rates of 0.26 and 0.25 ppb per year in Jeju and Ulleung, respectively.

In California, the contribution of background ozone to the ozone design value (ODV) has steadily increased, reaching approximately 70% in 2022 due to exponential decrease in anthropogenic ozone production. By comparison, the contribution of background ozone in background regions began to increase, starting in 2016, and reached about 50% in 2022. These findings underscore the importance of addressing background ozone in national air quality management strategies and offer a scientific basis for establishing effective mitigation policies.

Acknowledgments

This work was funded by the Korea Meteorological Administration Research and Development Program under Grant RS-2024-00404042.

How to cite: Lee, J. and Choi, W.: Long-Term Trends and Regional Differences in Background Ozone Concentrations in Korea: Insights from EEMD Analysis, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7984, https://doi.org/10.5194/egusphere-egu25-7984, 2025.

The Tropical West Pacific (TWP) is the key entry point of air into the stratosphere during Northern Hemispheric winter. Thus, the local air composition can influence global atmospheric chemistry and dynamics. Its interannual variability is itself affected by the El Niño Southern Oscillation (ENSO). The transport history of tropospheric air masses above the TWP is in particular reflected by the local ozone (O3) and relative humidity (RH) characteristics (Müller et al., 2024b).

We use regular balloon-borne profile measurements of these quantities from the Palau Atmospheric Observatory (PAO) to assess the (interannual) variability of TWP air masses and controlling processes (Müller et al., 2024a). Located in the centre of the tropical warm pool (7°N, 134°E) in Koror, Palau, the PAO has been filling a previous observational gap in this region since 2016 and has recently become a member of the SHADOZ (Southern Hemisphere Additional Ozonesondes) network. Our latest analysis of the PAO ozonesonde record showed how transport to the TWP mid-troposphere (5-10 km altitude) is modulated by the movement of the Intertropical Convergence Zone, allowing transport of polluted air masses from tropical Asia mainly between February and April into the otherwise clean air column (Müller et al. 2024b, Sun et al. 2023).

Here, we present an extended view on air mass transport to the region with a focus on the impact of ENSO on its interannual variability using an updated PAO time series (2016-2024), interhemispheric transport modelling using GEOS-Chem (Sun et al. 2023) and trajectory calculations from the Lagrangian Chemistry and transport model ATLAS (Wohltmann and Rex 2009). We found that very humid and ozone-poor air masses are suppressed in the free troposphere during El Niño. For La Niña conditions, the O3/RH distribution is shifted towards higher RH indicating enhanced convection compared to neutral conditions, but seasonal observations of dry ozone-rich air masses and long-range transport from Asia still occur.

The high convective activity in the TWP induces and maintains an ozone-poor humid tropospheric background. Its modulation by ENSO via sea-surface temperature and dynamical changes consequently either suppresses (El Niño) or strengthens (La Niña) the background composition. However, for the given time series the seasonal transport patterns prevail, which relate to a background composition of low O3 and high RH between July and October and dynamic disturbances of this background in form of dry ozone-rich layers between November and April.

How to cite: Müller, K., Röpke, T., Sun, X., Wohltmann, I., and Rex, M.: ENSO impact on mid-tropospheric composition above the Tropical Western Pacific via air mass transport, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11279, https://doi.org/10.5194/egusphere-egu25-11279, 2025.

Natural emissions, such as BVOCs and soil NOx, from tropical forests can affect tropospheric composition, reliant on the magnitude of emission and on what escapes from the canopy. In-canopy processes are not typically resolved in 3D regional or global models. Here, we investigate the diurnal variability of emissions, deposition and chemistry occurring at the ATTO site in the Amazon using the FORCAsT column model, which resolves the canopy space in 17 levels and extends above the boundary layer. Comparison to observations of meteorology and chemical species made at 8 heights confirms satisfactory performance of the model for the ATTO site. We explore the contribution of soil NOx to the atmospheric oxidative capacity above the canopy including its role in O₃ formation. In combination with canopy level deposition, we identify substantial deposition of NOx at the soil surface due to slow mixing at this height. In addition, at this dark level within the forest, NO reaction with O₃ is an important driver of chemistry. Finally, our model suggests buildup and net removal of NOx within the canopy overnight as mixing decreases, followed by release of NO in the morning. These findings reveal the role of in-canopy chemistry and deposition on above-canopy composition under pristine conditions, providing a baseline for comparison to polluted conditions and to global models without a resolved canopy.   

How to cite: Brown, F. and Heald, C.: The contribution of natural emissions to tropospheric composition above the Amazon, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16483, https://doi.org/10.5194/egusphere-egu25-16483, 2025.

How to cite: Biagi, B., Cuesta, J., Tanimoto, H., Kanaya, Y., Dufour, G., Beekmann, M., and Eremenko, M.: Multi-year evolution of tropospheric ozone pollution and its main drivers over East Asia during spring analyzed from multispectral satellite observations and in situ measurements, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15792, https://doi.org/10.5194/egusphere-egu25-15792, 2025.

Nitrogen oxides (NO_x), ozone (O₃), and carbon monoxide (CO) are important air quality indicators, while NO_x is also one of the main precursors of O₃. These trace gases have anthropogenic and natural sources at ground level and in the troposphere. At ground level, the main sources are transport emissions, industry, agriculture, and biomass burning. In the troposphere, additional sources include lighting and aircraft emissions and in the upper troposphere, downmixing from the stratosphere also makes a significant contribution to the ozone budget. Furthermore, the abundances of NO_x and O₃ in the troposphere are controlled by photochemistry.

The European Research Infrastructure IAGOS (www.iagos.org) uses in-service passenger aircraft as observation platforms, equipped with instruments to measure gaseous species, aerosols, and cloud particles. Since 2023 an IAGOS-CORE NO_x instrument (Package 2b) is installed aboard an IBERIA Airbus A330-200. Based in Madrid (Spain), this IAGOS-CORE aircraft covers routes to North, but mainly Central and South America. On the routes from Europe to Central and South America, the atmospheric abundances of the climate and air quality relevant trace gases CO, O₃, NO, NO₂, and NO_x were observed in the photochemically active region over the tropical Atlantic over the course of one year. From this unique dataset, we characterize the variability and the horizontal distribution of these trace gases across the Intertropical Convergence Zone and discuss the origin of the observed air masses.   

Acknowledgments: We thank all members of IAGOS-CORE, in particular IBERIA for enabling these IAGOS-CORE observations. The German Federal Ministry of Education and Research (BMBF) is acknowledged for financing the instruments operation and data analysis as part of the joint project IAGOS-D under grant 01LK1301A.

How to cite: Mahnke, C., Bundke, U., Houben, N., Schleiermacher, C., Galle, T., Nédélec, P., Sauvage, B., Thouret, V., Clark, H., and Petzold, A.: IAGOS in situ observations of NOx in the upper troposphere over the tropical Atlantic, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12725, https://doi.org/10.5194/egusphere-egu25-12725, 2025.

South and East Asia (S/E Asia), home to nearly half the world's population, are major contributors to global nitrogen oxide (NO_x = NO + NO₂) emissions due to recent rapid industrialization, urbanization, and growth in energy consumption. We compare tropospheric column NO₂ in the United Kingdom Chemistry and Aerosol (UKCA) model v11.0 with satellite measurements from NASA’s Earth Observing System (EOS) Aura satellite Ozone Monitoring Instrument (OMI) to investigate the seasonality and trends of tropospheric NO₂ over S/E Asia. UKCA is the atmospheric composition component of the UK Earth System Model (UKESM). UKCA was run with nudged meteorology, producing hourly output over S/E Asia for 2005–2015. OMI averaging kernels have been applied to the model hourly data sampled at Aura’s local overpass time of 13:45 ± 15 to allow consistent model-data comparison. Background UKCA and OMI tropospheric column NO₂ typically ranges between 0 – 2 × 10¹⁵ molecules/cm². Diurnal cycles and vertical profiles of the tropospheric NO₂ column in UKCA show that the daily minimum tropospheric column NO₂ occurs around the satellite overpass time. UKCA captures the seasonality but overestimates NO₂, by a factor of ~2.5, especially during winter over E China and N India, at times and locations with high aerosol loadings. Heterogeneous chemistry is represented in the version of UKCA used here as uptake of N₂O₅ on internally generated sulfate aerosol. However, aerosol surface area may be underestimated in polluted locations, contributing to overestimation of NO₂. In addition, the model may underestimate emissions of volatile organic compounds and associated peroxy acetyl nitrate (PAN) formation, leading to insufficient long-range transport of oxidised nitrogen, also contributing to overestimation of NO₂ over polluted regions and underestimation over remote regions. Quantifying and understanding discrepancies in modelled NO₂ warrant further investigation as they propagate into modelling of multiple environmental issues.

Keywords: Tropospheric NO₂; UKCA Model; Air Quality; Satellite Data; Climate Modelling

How to cite: Pandey, A. K., Stevenson, D., Zhao, A., Pope, R., Hossaini, R., and Kumar, K.: Tropospheric NO2 over South and East Asia measured by OMI and modelled by UKCA, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-975, https://doi.org/10.5194/egusphere-egu25-975, 2025.

The atmospheric monitoring station at Plateau Rosa, situated in the Central European Alps and part of the ICOS (Integrated Carbon Observation System) framework since 2021, is measuring methane mole fractions since 2018 with a cavity ring down spectrometer (Picarro G2301). Concentration measurements at this site, 3480 meter AMSL, are particularly valuable for tracking the atmospheric background and global trend of methane, but are also impacted by various source areas in Europe.

In this study, we analyzed the continuous record of methane mole fractions at the station, and we identified prolonged periods (more than 6 hours) of enhanced methane levels over the background that are associated with pollution events at regional scale. From 2020 until 2024, we detected 15 very pronounced pollution events, when air masses were coming mainly from central Europe and the UK. We used the FLEXPART atmospheric transport model coupled to the high-resolution (1 km x 1 km) output of the numerical weather prediction model COSMO to produce concentration footprints and simulate regional methane contributions. We assessed how well this transport model, coupled with different bottom-up inventories (EDGAR, TNO), can capture the selected pollution events. Finally, we compared the source areas identified with the TROPOMI satellite emission plumes measured in Europe.

We demonstrate how methane mole fraction data measured continuously at the station at Plateau Rosa can be used to attribute pollution events to specific regional source areas that might not be accounted by the inventories and are not detectable by satellite data.

How to cite: Zazzeri, G., Apadula, F., Henne, S., and Lanza, A.: The atmospheric station at Plateau Rosa: use of methane mole fractions and modelling to detect methane source areas in Europe, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8446, https://doi.org/10.5194/egusphere-egu25-8446, 2025.

This paper highlights the main findings of the twentieth annual Greenhouse Gas Bulletin (https://library.wmo.int/records/item/69057-no-20-28-october-2024) of the World Meteorological Organization (WMO). The results are based on research and observations performed by laboratories contributing to the WMO Global Atmosphere Watch (GAW) Programme (https://community.wmo.int/activity-areas/gaw).

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

Observations used for the global analysis are from 146 marine and terrestrial sites for CO₂, 153 for CH₄ and 112 for N₂O. The globally averaged surface mole fractions calculated on the basis of these observations reached new highs in 2023, with CO₂ at 420.0±0.1 ppm, CH₄ at 1934±2 ppb and N₂O at 336.9±0.1 ppb. These values constitute, respectively, increases of 151%, 265% and 125% relative to pre-industrial (before 1750) levels. The increase in CO₂ from 2022 to 2023 (2.3 ppm) was slightly higher than the increase observed from 2021 to 2022 and slightly lower than the average annual growth rate over the last decade, which was most likely partly caused by natural variability, as fossil fuel CO₂ emissions have continued to increase. This increase marked the twelfth consecutive year with an increase greater than 2 ppm.

The Bulletin reports that within-year variability of CO₂ was 2.8 ppm in 2023, the fourth largest within-year annual increase since modern CO₂ measurements started in the 1950s. Such increase may be a result of enhanced fire emissions and reduced net terrestrial carbon sinks. The CO₂ growth rate varies from year to year (between 2.1 and 3.2 ppm during 2014-2023), with the variability mostly driven by the terrestrial biosphere exchange of CO₂, as confirmed by measurements of the stable carbon isotopes ratio, ¹³C:¹²C in atmospheric CO₂. Coincidental with the large CO₂ increase during 2023 was the largest increase in atmospheric carbon monoxide (CO) in the past two decades, suggesting enhanced CO₂ emissions from fires.

The increase of CH₄ mole fraction from 2022 to 2023 (11 ppb) was lower than that observed from 2021 to 2022 but still slightly higher than the average annual growth rate over the last decade. The record rise in atmospheric CH₄ from 2020 to 2022 was accompanied by a significant drop in atmospheric δ¹³C_CH4. The unexpected change in the amount of atmospheric δ¹³C_CH4 is best explained by a transition from fossil fuels to microbial emissions as the dominant driver of increasing CH₄. Moreover, the geographic distribution of CH₄ growth from 2020 to 2022 suggest strong increases in isotopically light emissions from tropical and boreal wetland areas, which is indicative of positive climate feedback on CH₄ emissions in response to climate transition to an El Niño phase in 2023.

In the near future, climate change itself could cause ecosystems to become larger sources or sinks of GHGs. Identifying and tracking the potential climate feedbacks require continued high accuracy observations also at currently undersampled regions.

How to cite: Tarasova, O., Vermeulen, A., Lan, X., and Tsuboi, K.: The state of greenhouse gases in the atmosphere using global observations through 2023, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8610, https://doi.org/10.5194/egusphere-egu25-8610, 2025.

Trifluoroacetic acid (TFA), a short chain perfluorocarboxylic acid (scPFCA), is a contaminant of emerging concern because its emissions are projected to rapidly increase, it is highly persistent, and remediation is challenging. Recent studies based on ice core records report large increases (up to a factor of ~10) in Arctic TFA deposition since the 1970s. The ice core temporal trends suggest that CFC replacement gases introduced following the Montreal Protocol could be an important source. However, TFA is a “substance from multiple sources” and their relative importance remains poorly quantified; a challenge which needs to be addressed for the emission trend to be reversed through regulation. Here we use a chemical transport model (FRSGC/UCI-CTM) to examine the global TFA budget from the production of long-lived source gases, namely, hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), and inhalation anaesthetics. A detailed degradation scheme describing TFA production from each precursor was added to the model and simulations performed using time-varying loadings of its major emitted precursors. Model results showed that TFA production from CFC-replacements increased by a factor of four from 2000 (6.3 Gg/yr) to 2016 (25.4 Gg/yr), with cumulative deposition over this period reaching 226 Gg/yr. HCFC-123, HCFC-124, and HFC-134a account for the majority of this production. TFA deposition shows a latitudinal dependence with the majority occurring in extrapolar regions. Model results are compared to measurements from ice core data and precipitation concentrations. While demonstrating the increasing contribution of CFC replacements to TFA, we highlight the challenges in elucidating their significance against other sources from sparse TFA measurements records, particularly in regions where TFA deposition is highest.

How to cite: Hart, L., Hossaini, R., and Wild, O.: Rising Trifluoroacetic Acid Levels: Evaluating Contributions from long-lived CFC replacements and anaesthetics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17312, https://doi.org/10.5194/egusphere-egu25-17312, 2025.

Chlorine dioxide (OClO) is a by-product of the ozone depleting halogen chemistry in the stratosphere. Although being rapidly photolysed during daytime, it plays an important role as an indicator of the chlorine activation in polar regions during polar winter and spring under twilight conditions because of the nearly linear dependence of its formation on chlorine oxide (ClO).

The TROPOspheric Monitoring Instrument (TROPOMI) is an UV-VIS-NIR-SWIR instrument on board the Sentinel-5P satellite developed for monitoring the composition of the Earth’s atmosphere. Launched on 13 October 2017 in a near polar orbit, it provides    continuous monitoring possibilities for many constituents including the observations of OClO at an unprecedented spatial resolution.

We analyze the time series (2017 – 2025) of slant column densities (SCDs) of chlorine dioxide (OClO) at polar regions. Especially we focus on the higly variable conditions in the NH polar region by comparing the OClO timeseries with meteorological data. This allows us to investigate the conditions under which the chlorine activation starts and ends.

How to cite: Pukite, J., Ziegler, S., and Wagner, T.: Chlorine activation as seen by TROPOMI OClO 2017 – 2025 measurements, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12166, https://doi.org/10.5194/egusphere-egu25-12166, 2025.

Stratospheric bromine originates partly from natural and partly from anthropogenic sources. After the Montreal protocol and following amendments, anthropogenic emissions (halons and methyl bromide) were largely reduced. This reduction was not only seen in tropospheric in situ measurements, but also in a reduction of stratospheric bromine levels (estimated from BrO measurements) after about 2002.

Here, we report on ground-based observations of stratospheric BrO carried out between 1995 and present in Kiruna (northern Sweden). The (slant) column density of BrO is analysed from UV spectra of zenith scattered sun light at solar zenith angles of 80° and 90°. Our measurements are in agreement with predictions predictions and existing observational data sets for the period before about 2019 for which a steady decline of the BrO levels is found. However, after 2019 the stratospheric BrO levels increased again, in contrast to the expected trend. The reason for this discrepancy is not yet known. Possible explanations might be increasing natural emissions of methyl bromide and/or very short lived bromine containing compounds, perhaps related to climate change (e.g. a warmer sea surface). Also recently again increasing anthropogenic emissions of methyl bromide might contribute. The variation of stratospheric aerosols is unlikely to explain the changed trend after 2019.

How to cite: Wagner, T., Gu, M., Enell, C.-F., Lauster, B., Mies, K., Otten, C., Platt, U., Pukite, J., Raffalski, U., and Ziegler, S.: Trends of stratospheric BrO (1995 to 2025) derived from ground-based DOAS observations at Kiruna, Northern Sweden, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4456, https://doi.org/10.5194/egusphere-egu25-4456, 2025.

In the troposphere, N₂O is among the most important anthropogenic greenhouse gases, with its long lifetime and a global warming potential in the order of 300 times higher than the same mass of CO₂. Furthermore, in the stratosphere, it is the primary ozone(O₃)-depleting gas not regulated by the Montréal protocol. As N₂O’s anthropogenic emissions grow, its impact on the Earth’s climate also increases. This paper investigates the dynamics of both N₂O and O₃ in the lower stratosphere using data from the Aura satellite’s MLS (Microwave Limb Sounder) instrument which has been gathering data for both gases since 2004. The study focuses on the lower stratosphere (pressures between 68-22 hPa, corresponding to ~18-26 km at the equator), at 30 selected locations above equatorial and temperate land regions. Both long-term increase and positive correlations between simultaneous N₂O and O₃ concentrations were examined. The results showed weak increase for O₃ and more noticeable ones for N₂O, with the latter also including some negative trends, though that is likely related to the MLS instrument’s age. Regarding the relationship between N₂O and O₃, it was found that the correlation between the gases changes with altitude differently depending on the latitude of the study region. Near the equator, almost no correlation between the gases at 68 hPa level was found but as altitude increases, a negative correlation was observed; it increased up to at least 22 hPa level. At higher latitudes, an inverted version of this phenomenon was observed – negative correlations at lower altitudes first weakened and were afterwards replaced by positive correlations as altitudes increased.

How to cite: Põlgaste, S., Aun, M., and Mander, Ü.: Regional dynamics and trends of N2O and O3 in the lower stratosphere, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18852, https://doi.org/10.5194/egusphere-egu25-18852, 2025.

Stratospheric Ozone (O3) absorbs biologically harmful solar ultraviolet radiation, mainly in the UV-B and UV-C spectral range. When reaching the surface, such UV radiation poses a well documented hazard to human health. In order to quantify this amount of UV radiation and to make it generally understandable, the World Health Organization (WHO) has defined an UV Index [1]. It is calculated by weighting the incoming solar irradiance at surface level between 250 and 400 nanometers with their ”harmfulness” to the skin and scaling the results to values that normally range between 1 and 10, surpassing 10 for excessive UV exposure.

In our project we extend the capability of ICON (ICOsahedral Nonhydrostatic Model,[2]), the operational forecast model used by the German Meteorological Service, to provide a configuration of self-consistent UV Index forecasts that do not require external data. For this, we use ICON-ART [3],[4] with a linearized prognostic ozone scheme (LINOZ,[5]) and couple the prognostic ozone to the atmospheric radiation scheme Solar-J [6].

With this setup, we define a global test run from March to July 2022. This time frame contains distinct ozone features above Europe due to the polar vortex as well as its breakup and the transition to the summer circulation. We use the results to validate the UV Index forecast with respect to  parameters that influence it, e.g. aerosol optical depth, surface albedo, or cloud cover. For the comparison we use other model data (CAMS,[7]) as well as ground-based and satellite measurements (e.g. CERES,[8]).

References:

[1] World Health Organization and World Meteorological Organization and United Nations Environment Programme and International Commission on
Non-Ionizing Radiation Protection. Global solar UV Index : a practical guide, 2002.
[2] G. Zängl, et al. The ICON (icosahedral non-hydrostatic) modelling framework of dwd and mpi-m: Description of the non-hydrostatic dynamical core. Quarterly Journal of the Royal Meteorological Society, 141(687):563–579, 2015.
[3] J. Schröter, et al. ICON-ART 2.1: a flexible tracer framework and its application for composition studies in numerical weather forecasting and
climate simulations. Geoscientific Model Development, 11(10):4043–4068,2018.
[4] D. Rieger, et al. ICON–ART 1.0 – a new online-coupled model system from the global to regional scale. Geoscientific Model Development, 8(6):1659–1676, 2015.
[5] C. A. McLinden, et al. Stratospheric ozone in 3-d models: A simple chemistry and the cross-tropopause flux. Journal of Geophysical Research: Atmospheres,105(D11):14653–14665, 2000.
[6] J. Hsu, et al. Aradiative transfer module for calculating photolysis rates and solar heating in climate models: Solar-j v7.5. Geoscientific Model Development, 10(7):2525–2545, 2017.
[7] CAMS Global Atmospheric Composition Forecasts, https://ads.atmosphere.copernicus.eu/datasets/cams-global-atmospheric-
composition-forecasts?tab=overview, 01 2025.
[8] NASA/LARC/SD/ASDC. CERES and GEO-Enhanced TOA, Within-Atmosphere and Surface Fluxes, Clouds and Aerosols 1-Hourly Terra-Aqua
Edition4A, 09 2017.

How to cite: Hanft, V., Ruhnke, R., Seifert, A., and Braesicke, P.: Prognostic Ozone For ICON: Enabling UV Forecasts, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11261, https://doi.org/10.5194/egusphere-egu25-11261, 2025.

Polar regions are strategic in the study of stratospheric long-term ozone trends: since these regions are highly impacted by the effective-chlorine levels, the ozone recovery expected from the reduced emission of ozone depleting substances (Montreal Protocol) should be observed most easily there. However, contrary to the Antarctic, positive ozone trends have not yet been observed in the Arctic (WMO 2022) due to the higher natural variability of ozone in that region. Studying tropospheric ozone trends in the Arctic is also crucial because it can help in reconciling total and stratospheric ozone trends, additionally to the intrinsic interest in ground-level ozone as one of the main greenhouse gases.

The Network for the Detection of Atmospheric Composition Change (NDACC) provides amongst others long-term ozone data from Fourier Transform Infrared (FTIR) spectrometers as well as ozone sonde instruments. We present long-term trends (2000-2022) for total, stratospheric and tropospheric ozone from seven FTIR ground-based stations and from seven ozone sonde stations in the Arctic. The FTIR stratospheric trends are provided in three different layers, covering the lower stratosphere up to 45 km, according to the FTIR vertical resolution.  Based on a previous representativeness study, we also obtain regional trends with reduced uncertainties by combining different instruments and stations. Annual and seasonal trends are calculated using a multiple linear regression technique involving a set of proxies that represent physical processes influencing the natural ozone variability. Using this network of ground-based measurements, we further validate tropospheric and stratospheric ozone trends in the Arctic as derived from satellite observations (MEGRIDOP, SUNLIT, IASI).

How to cite: Jonas, C., Björklund, R., Vigouroux, C., De Mazière, M., Langerock, B., Boynard, A., Hannigan, J. W., Jepsen, N., Kivi, R., Lyall, N., Mellqvist, J., Palm, M., Sofieva, V., Strong, K., Tarasick, D., and Virolainen, Y.: Looking for ozone recovery in the Arctic, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18197, https://doi.org/10.5194/egusphere-egu25-18197, 2025.

The primary objective of this work is to analyze the temporal and spatial characteristics of the Ozone Effective Temperature (Teff). This study utilized Teff data derived from the Tropospheric Emission Monitoring Internet Service (TEMIS; https://www.temis.nl/climate/efftemp/overpass.php). The dataset includes daily values spanning the period from 1961 to 2023, providing an extensive temporal coverage. To ensure a comprehensive and representative analysis, the study examined data from 358 sites. These sites were carefully selected to achieve uniform coverage across all latitudinal and longitudinal zones.

To explore the spatiotemporal distribution of Teff, detailed spatial analyses were conducted. The results include essential statistical measures for each site, such as the mean Teff values and their standard deviations. Additionally, a thorough spatiotemporal analysis of the time series was performed, highlighting variations and differences across distinct geographical zones. The study also examines trends in Teff over time, providing insights into the evolution of Ozone Effective Temperature across various latitudinal zones.

This multifaceted approach not only reveals significant patterns and trends in Teff but also underscores its variability and differences between regions, contributing to a deeper understanding of its global behavior. The inclusion of statistical and trend analyses further enhances the robustness and relevance of the findings.

How to cite: Christodoulakis, J., kouremadas, G., and Goudas, K.: A study of the ozone effective temperature temporal and spatial features, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19881, https://doi.org/10.5194/egusphere-egu25-19881, 2025.

The widespread distribution of pesticides in the global atmosphere has been well-documented, posing significant threats to ecosystems and human health, particularly from highly hazardous pesticides (HHPs) characterized by elevated toxicity and/or persistence. Recent studies suggest that certain environmental transformation products of pesticides may be even more hazardous than their precursors. However, related knowledge remains limited currently, hindering our comprehensive assessment and effective response.
Here, we developed a pseudo-targeted analysis strategy designed for rapid-response scenarios, enabling the identification of thousands of pesticide-related compounds in air samples using high-resolution mass spectrometry. Applying this framework to the North China Plain, a key agricultural and densely populated region, we conducted monthly sampling over one year and identified 127 pesticides and transformation products in the local atmosphere. Distinct seasonal variations (monthly fluctuations) and spatial distributions (urbanization gradients) were observed, highlighting agricultural activities as the primary drivers of atmospheric pesticide levels.
Risk assessments for humans and animals were conducted based on environmental concentrations and toxicological data. By comparing concentrations in the organisms with internal effect concentrations, we quantified risk values and found that atmospheric pesticide risks in the North China Plain are unacceptable under some specific situation. Notably, the nonlinear relationship between total concentration and risk values underscores the dominant role of HHPs.
The HYSPLIT model was employed to identify the transport pathways and potential sources of atmospheric pesticides. The results indicate that the North China Plain experiences both external inputs and intercity migration within the region, with Eurasia and the Pacific Ocean potentially serving as sources of atmospheric pesticides.

How to cite: Zhao, M., Chen, D., Wu, J., Figueiredo, D., Rezaei, M., Ritsema, C., Li, L., Liu, Q., Zhao, F., Han, J., Liu, X., and Wang, K.: Occurrence and risk of atmospheric pesticides in Northern China, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20042, https://doi.org/10.5194/egusphere-egu25-20042, 2025.