PICO
Researchers are invited to present novel scientific results from mid- and long-term observational time series from various programmes and networks such as the Global Atmosphere Watch (GAW) Programme, European Monitoring, and Evaluation Programme (EMEP), Network for the Detection of Atmospheric Composition Change (NDACC), Southern Hemisphere Additional Ozonesondes (SHADOZ), Advanced Global Atmospheric Gases Experiment (AGAGE), National Oceanic and Atmospheric Administration (NOAA), regular airborne (e.g. CARIBIC, IAGOS, CONTRAIL) and other campaigns as well as satellite data and model simulations. Data relevant to tropospheric and stratospheric composition, in particular, related to climate change, ozone depletion, ecosystems and health impacts, and air quality as well as firn data on past atmospheric composition are welcome. We welcome contributions from multi-year modeling studies and inter-comparison exercises that address past and future tropospheric or stratospheric composition changes, carried out in the framework of international projects and initiatives.
Large-scale ozone episodes over Europe are influenced by complex interactions between meteorology and precursor availability, whose relative importance varies across regions and seasons. This study investigates the spatial distribution and drivers of the 100 largest ozone episodes identified in the Copernicus Atmosphere Monitoring Service (CAMS) global reanalysis over Europe during April–September 2003–2022.
First, ozone extremes are identified as exceedances of the local 95th percentiles of daily ozone maxima. A semi-Lagrangian algorithm is employed to merge them as daily patterns and then into ozone episodes if they are connected in space and time. This enables a robust characterisation of their spatial extent and temporal evolution. We find that large ozone episodes mainly affect regions north of around 48° N in Apr-May and south of 54° N in Jun-Sep, clustering in three key regions: the British Isles (BRIT) and Eastern Europe (EEU) during Apr-May, and a large region that covers Central Europe (CEU) in Jun-Sep. Additional meteorological and chemical data, as well as an algorithm for the identification of atmospheric blocking and subtropical ridges, are used to assess the role of meteorological processes and precursor emissions in the formation of ozone episodes in these regions and seasons.
In EEU, ozone episodes are favoured by well-defined anticyclonic conditions, although elevated precursor concentrations, frequently linked to biomass burning, are also required. In contrast, large episodes affecting BRIT occur under atypical synoptic conditions characterized by negative anomalies of 500 hPa geopotential height and daily maximum temperature at 2 m as well as stronger than usual winds. The potential reasons for these unexpected results are discussed. In CEU, we identify significant north-south differences: episodes in northern CEU are strongly influenced by persistent blocks and ridges, while those in the south are associated with weaker synoptic forcing, with enhanced subsidence as the main contributing mechanism. These findings are relevant for future air quality assessments as they demonstrate that the occurrence of large-scale ozone episodes in Europe is driven by region-specific combinations of meteorological conditions and precursor availability.
How to cite: Fuentes-Alvarez, T., Ordóñez, C., García-Herrera, R., Barriopedro, D., Crespo-Miguel, R., and Lima, M. M.: The 100 largest surface ozone episodes in Europe during 2003–2022: role of meteorology and emissions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1814, https://doi.org/10.5194/egusphere-egu26-1814, 2026.
How to cite: Ma, Z. and Liao, Z.: Meteorology-normalized ozone enhancement during the 2022 late-spring COVID-19 lockdown in Beijing, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2409, https://doi.org/10.5194/egusphere-egu26-2409, 2026.
Tropospheric ozone (O₃) is a key oxidant and secondary pollutant that influences air quality and radiative forcing. Understanding its variability is crucial in regions highly sensitive to climate change, such as Antarctica, where complex interactions among stratosphere–troposphere exchange, air mass origin and local meteorology govern O₃ dynamics. Detailed characterisations of ozone vertical profiles under specific airflow regimes remain limited, especially for western Antarctica. This study analyses a comprehensive 25-year dataset (1999–2023) of ozone and meteorological profiles (754 in total) collected at Belgrano II station (77.87° S, 34.62° W). The objective is to characterise the vertical distribution of tropospheric ozone in western Antarctica and identify the main drivers of its variability.
Atmospheric transport and synoptic conditions were assessed using seasonal 850 hPa geopotential height maps and HYSPLIT back trajectories. A homogenisation procedure enabled the computation of seasonal and monthly means and long-term trends. The region is influenced by the Antarctic Polar Anticyclone, semi-permanent cyclones over the Weddell and Amundsen–Bellingshausen Seas, and persistent katabatic winds from the Antarctic Plateau. Four distinct transport regimes were identified: strong marine influence from the Weddell Sea, continental flows from northern and southern sectors, and mixed marine–continental influence over the Antarctic Peninsula.
Seasonal analysis of tropospheric ozone revealed increasing concentrations with altitude, ranging from ~20–30 ppb near the surface to ~45–55 ppb in the upper troposphere. O₃ concentrations peaked in winter (~25–35 ppb at low levels, ~45–50 ppb aloft) and early spring (~28–38 ppb at low levels, ~50–55 ppb aloft), while lower values were observed in summer (~20–25 ppb at low levels, ~40–45 ppb aloft) and autumn (~22–28 ppb at low levels, ~42–48 ppb aloft). These variations reflect the interplay of reduced photochemical destruction, enhanced stratosphere–troposphere exchange under the polar vortex, and increasing solar radiation during spring and summer.
Lower-tropospheric O₃ profiles (950–700 hPa) were modulated by transport regime. Highest mean concentrations occurred under purely marine flows from the Weddell Sea (29.8 ± 1.2 ppb), while Weddell–Antarctic Peninsula flows showed the lowest values (23.5 ± 1.7 ppb) due to topographic effects and halogen-driven ozone depletion. Continental flows exhibited intermediate levels (Northern: 26.9 ± 1.5 ppb; Southern: 24.3 ± 1.4 ppb). Finally, analysis of monthly mean profiles over the past two decades revealed a modest increase throughout the troposphere, below 1 ppb dec⁻¹.
These results highlight the combined influence of large-scale circulation, local dynamics, and seasonal processes on Antarctic tropospheric ozone and provide a baseline for evaluating future changes in the western Antarctic troposphere.
How to cite: Adame, J., Navarro-Comas, M., Ochoa, H., Prados-Roman, C., and Yela, M.: Tropospheric ozone in western Antarctica driven by synoptic-scale transport over 25 years at Belgrano II station, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4775, https://doi.org/10.5194/egusphere-egu26-4775, 2026.
Arctic surface ozone (O3) is an important short lived climate forcer as it interacts with light both in the solar light and in the infrared region and thus it plays an important role during Arctic summer. Surface O3 in the High Arctic exhibits substantial variability during summer months, driven by complex interactions between photochemistry, long-range transport, and boundary layer dynamics. Understanding the relative contributions of these processes and their long-term changes is critical for interpreting observed O3 variability and projecting future changes under rapid Arctic climate warming. We present a comprehensive analysis of summertime (June-August) O3 at a high Arctic monitoring station in North-east Greenland (Villum Research Station) spanning three decades (1995-2024), combining advanced statistical decomposition methods, back trajectory analysis, data-driven Bayesian modeling for entrainment detection, and chemical transport model simulations to quantify the major processes controlling surface O3 concentrations and assess their temporal evolution. Long-term analysis using traditional (Mann-Kendall test and Sen’s slope) and STL (Seasonal-Trend decomposition using Loess) reveals complex temporal patterns in summertime O3 and its baseline concentrations over the 30-year period, with substantial interannual variability. STL decomposes the time series into baseline, seasonal component, and residuals, enabling process-specific analysis. Back trajectory analysis comparing high versus low O3 episodes identifies distinct source regions and transport pathways. Trajectories are categorized by surface type (land, snow, sea ice, ocean) and altitude (within versus above mixing layer). High O3 episodes are predominantly associated with air masses from above the mixing layer and open ocean, whereas low O3 periods show dominant patterns indicating sea ice and land sources. To quantify local boundary layer entrainment processes, we apply automated entrainment detection on the STL residuals, which isolate short-term variability after removing baseline and seasonal components. Entrainment events bring O3-rich free tropospheric air to the surface, characterized by simultaneous O3 increases, relative humidity (RH) decreases at 9m, and enhanced vertical RH gradients. A two-stage Bayesian inference approach is developed to first screens candidates using physical thresholds, following by probabilistically estimates event timing, magnitude, and persistence while accounting for measurement uncertainty. We analyze temporal patterns in entrainment frequency and magnitude over the three decades to assess potential changes in boundary layer dynamics. To complement the observational analysis, we employ the Danish Eulerian Hemispheric Model (DEHM), a chemical transport model, to perform long-term O3 simulations. The model quantifies stratospheric contributions to surface O3 and enables evaluation of how well current chemical transport schemes capture the observed variability and process attribution identified through the statistical and trajectory analyses. This integrated approach provides robust process attribution and understanding by linking observed O3 to air mass origin, transport characteristics, vertical mixing, and stratospheric inputs, demonstrating that Arctic O3 variability results from complex interplay of hemispheric transport, local meteorology, and boundary layer dynamics.
How to cite: Ye, Z., Pernov, J. B., Hjorth, J. L., Christensen, J. H., Hansen, K. M., and Skov, H.: Processes influencing summertime ozone concentrations at a high Arctic site, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12567, https://doi.org/10.5194/egusphere-egu26-12567, 2026.
The Chilean Atacama desert hosts the largest astronomical observatories world-wide due to its unique dry meteorological conditions and high altitude of the Andes. One of the largest facilities is Cerro Paranal, among others hosting the Very Large Telescope, which is equipped with several spectrographs ranging from the ultraviolet to the mid-infrared. As ground-based telescopes have to observe through the Earth's atmosphere, the spectra taken from astronomical objects are affected by molecular absorption arising from the present various species. This imprint -called telluric contamination- varies in the same way as the composition of the Earth's atmosphere varies. Therefore it is of crucial importance for astronomers to know about the chemical components of the atmosphere at the time of observation to be able to correct for these contaminations.
In the past, mostly static atmospheric standard models were used to fit and correct the telluric contaminations. In the meanwhile, several sources of world-wide, time-dependent information of the chemical composition are available. We are currently investigating data from the Copernicus Atmospheric Monitoring Service (CAMS) Global Reanalysis (EAC4) and CAMS Global Greenhouse reanalysis (EGG4), which provide height profiles of various molecular species (e.g. NO, NO2, O3, CO, HNO3,...) on a 3-hourly resolution ranging from 2003 through 2020 (EGG4) and 2024 (EAC4). This allows us a detailed analysis on the hourly, daily, seasonal, and yearly variability of the chemical composition of the Earth’s atmosphere above Cerro Paranal.
We found significant variations of nearly all species on various time scales, highly affecting the astronomical observations. In this presentation we show first results of our investigations. As astronomical observations are conducted during night, we focus on day/night-time differences and long-term trends to estimate the impact on telluric contamination.
How to cite: Kausch, W., Kimeswenger, S., Smette, A., and Noll, S.: The atmospheric composition variability above Cerro Paranal/Chile, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9744, https://doi.org/10.5194/egusphere-egu26-9744, 2026.
Nitrogen oxide (NOX) is an important air quality indicator and one of the main precursors of ozone (O3). These trace gases have natural and anthropogenic 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.
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. The IAGOS-CORE NOx instrument (Package 2b) is designed to measure NO, NO2, and total NOX. Since its operation started on one Lufthansa aircraft in 2015 and further expansion of the fleet in 2023, a fourth aircraft was equipped with this instrument type in 2025. These four IAGOS-CORE aircraft from Air France, China Airlines, Iberia, and Lufthansa cover routes to North, Central and South America, Europe, Africa and Asia. From this unique in situ measurements, we discuss the vertical NOX profiles from ground up to about 12 km altitude. Thereby we are not only focusing on the abundance of NOX within the planetary boundary layer but also how NOX is distributed in the free troposphere and how this vertical distribution varies globally above different metropolitan aeras. Cities such as New York, Montevideo, Frankfurt, Madrid, Hong Kong, Taipei, and Tokyo were selected to represent different global regions and have a statistical base of at least ten and up to about 300 individual profiles for each city available.
Acknowledgments: We thank all members of IAGOS-CORE, in particular the airlines for enabling these IAGOS-CORE observations. The data were created with support from the European Commission, national agencies in Germany (BMBF), France (MESR), and the UK (NERC), and the IAGOS member institutions (http://www.iagos.org/partners).
How to cite: Mahnke, C., Bundke, U., Houben, N., Schleiermacher, C., Galle, T., Rohs, S., Nédélec, P., Thouret, V., Clark, H., Wang, K.-Y., Tanimoto, H., and Petzold, A.: The vertical distribution of NOx and its variability above metropolitan areas in America, Europe, and Asia, as observed by IAGOS, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12272, https://doi.org/10.5194/egusphere-egu26-12272, 2026.
The prediction of nitrogen dioxide (NO₂) concentration is crucial for protecting human health and controlling environmental pollution. However, the complex temporal patterns and rapid time fluctuations pose significant challenges to accurate NO₂ forecasting. Some existing studies have introduced machine learning techniques like Recurrent Neural Networks (RNNs) and Long Short-Term Memory (LSTM) networks to extract richer temporal features, while they are still struggling with effectively capturing long-term dependencies. Moreover, most studies focus primarily on individual monitoring stations, often overlooking the spatial correlations between stations, which limits the ability to make comprehensive predictions for larger regions. To address these issues, this study expands the scope to include all monitoring stations across China. By employing Transformer models, we aim to extract long-term dependencies at multiple temporal scales while incorporating spatial and attributive distances to facilitate information sharing among different monitoring stations. Our objective is to achieve holistic prediction of NO₂ concentrations nationwide and make analysis for the future trend. The findings of this research are expected to provide valuable theoretical support for proactive environmental pollution management and prevention.
How to cite: Xiao, M. and Huang, B.: Transformer-based forecasting of national NO₂ concentrations with spatiotemporal and attributive dependencies, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13107, https://doi.org/10.5194/egusphere-egu26-13107, 2026.
Tropospheric nitrogen dioxide (NO2) is an indicator of anthropogenic activity and a key precursor of the phytotoxic surface ozone (O3), with potential implications for agricultural ecosystems. Recent satellite-based studies have reported negative association between NO2 and vegetation greenness over agricultural regions, but the persistence of these relationships over longer timescales and their relevance for crop photosynthetic functioning remain unclear. Here, we assess co-variability between NO2 and photosynthetic activity over Indian croplands (rice and wheat dominated regions) over a decadal scale (2007–2022) using High Spatial-Temporal Coverage Merged tropospheric NO2 (HSTCM-NO2) dataset and Solar Induced Fluorescence (SIF) from the Global Solar-induced Chlorophyll Fluorescence (GOSIF) product. Analyses conducted separately for the kharif (July–September) and rabi (January–March) seasons to account for contrasting agro-climatic and photochemical conditions. We find widespread increases in SIF for rabi season croplands (0.0032 W/m²/μm/sr/yr) including wheat-dominated regions, despite spatially heterogeneous NO2 trends (0.0096×1015 molec./cm2/yr) that increase across much of the Indo-Gangetic Plain (IGP). However, analysis of detrended interannual variability reveals a significant negative association between NO2 and SIF during the rabi season (Pearson correlation, r=-0.5, p=0.048), indicating reduced photosynthetic activity in years with elevated pollution. A similar but weaker relationship is observed for kharif season croplands in rice-dominated regions (r=-0.1, p=0.704). The results indicate that variations in NO2 pollution may modulate interannual crop performance by influencing photosynthetic activity, even in systems where long-term productivity trends are primarily driven by management and technology.
Keywords: Tropospheric NO2; Pollution; Croplands; Photosynthetic activity; SIF; India
How to cite: Kunhimuthappan Suresan, A. and Kuttippurath, J.: Assessment of the relationship between tropospheric NO2 and photosynthetic activity across seasonal croplands in India, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16228, https://doi.org/10.5194/egusphere-egu26-16228, 2026.
Wildfires are a significant source of trace gases and aerosols emitted into the atmosphere with the potential to influence the Earth’s radiative balance, and therefore climate. To assess their present-day influence on atmospheric composition, we conducted multi-year simulations using a range of emissions datasets over the period 2003-2015.
In our study we employ TM5-MP Chemical Transport Model (CTM) and five biomass burning (BB) emissions datasets: GFED4.1s, GFASv1.2, FEERv1.0-G1.2, QFEDv2.4r1 and FINNv2.5, to drive the simulations. This intercomparison aims to assess the model's ability to simulate atmospheric composition and wildfire-driven changes in atmospheric tracers such as carbon monoxide (CO), nitrogen oxides (NOx), ozone, and aerosol abundances, distribution, seasonal cycles, and interannual variability (IAV), while examining the dependency of the results on the input wildfire emissions dataset. Hot-spots of wildfire influences are identified, and results are compared with satellite and ground-based observations, to examine where the model captures the role of biomass burning emissions in the atmosphere more accurately and where deficiencies are evident.
Comparing results for CO, high IAV is captured in BB hotspots in the corresponding BB season, with simulations using FEER showing the lowest IAV of all datasets. Simulated Aerosol Optical Depth (AOD) shows pronounced IAV in Siberia (boreal spring/summer), South America (boreal summer/autumn) and Boreal North America (boreal summer), across all datasets, albeit, with different magnitudes. These patterns align with the seasonal burning in each region; when fire emissions are excluded, AOD IAV decreases significantly during the corresponding burning seasons.
How to cite: Paraskevopoulou, K., Vamvakaki, C., Myriokefalitakis, S., Mourgela, R.-N., Petrakis, M. P., Seiradakis, K., and Voulgarakis, A.: Multi-Year Simulations of the Global Atmosphere: The role of Biomass Burning Emissions Datasets, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18877, https://doi.org/10.5194/egusphere-egu26-18877, 2026.
Carbon monoxide (CO) is an important indirect greenhouse gas, plays a key intermediate role in the cycling of carbon compounds in the atmosphere and via these reactions affects the atmospheric oxidation capacity. Its sources and sinks can be (partially) distinguished with isotope measurements, but extensive observations of CO isotopic composition are sparse. A network of independent global observatories monitored 𝛿13CCO and 𝛿 18OCO at the turn of the 21st century. Since this time, the sole continuous monitoring of CO isotopic composition has been carried out at Baring Head, New Zealand. Starting in 2023, as part of the ISAMO project, we have resumed regular measurements of 𝛿13CCO and 𝛿 18OCO at seven global monitoring stations, with a focus on the tropical Atlantic. The goal of ISAMO is to better constrain the proposed pathway of methane removal via chlorine radicals that can be released photochemically from mixed mineral dust - salt aerosols. Here we use the new and existing CO isotope data together with model simulations to derive empirical constraints for the production rate of CO from the CH4 + Cl reaction. In addition, we will demonstrate how CO isotope measurements can be used to constrain long-term, and episodic, changes in the global and regional CO budget, arguing for sustaining such measurements at globally distributed locations.
How to cite: Röckmann, T., Brashear, C., Gromos, S., van Herpen, M., Yu, X., van der Veen, C., van Asperen, H., Zaehle, S., Moossen, H., Jordan, A., Meidan, D., Saiz-Lopez, A., Sperlich, P., Moss, R., Mak, J., Petron, G., Crotwell, A., Johnson, M., and D'Amico, F. and the The ISAMO team: Using stable isotope of measurements of carbon monoxide for constraining short- and long-term changes in its global budget and atmospheric chemistry, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21821, https://doi.org/10.5194/egusphere-egu26-21821, 2026.
The natural landscape has undergone profound transformations due to human activities, with vast areas being converted for agriculture and grazing. This shift has far-reaching consequences for the Earth's system, impacting various components such as surface reflectivity, roughness, evapotranspiration, and atmospheric composition.
To better understand the effects of land cover change on atmospheric chemistry, this study employs the chemistry–climate model EMAC to simulate two distinct scenarios. The first scenario represents the current state of land cover, characterized by widespread deforestation for agricultural and grazing purposes, with the potential natural vegetation (PNV) cover simulated by the model. In contrast, the second scenario depicts an extreme reforestation scenario, where grazing land is restored to its natural state.
The results of this study reveal that the expansion of agricultural land leads to a decline in global emissions of biogenic volatile organic compounds (BVOCs). This decrease in BVOC emissions, in turn, results in higher surface concentrations of hydroxyl radicals (OH, +5.7%) and lower mixing ratios of carbon monoxide (CO, -6.2%). Notably, this trend persists despite increased CO emissions from agricultural biomass burning.
At the same tim, the mixing ratios of nitrogen oxides (NOx) exhibit an increase (+7.8%) due to enhanced anthropogenic and natural soil sources. While regional ozone responses may vary, the global ozone production sensitivity shifts from a NOx- to a VOC-sensitive regime.
These changes have significant implications for radiative forcing, with reductions in tropospheric ozone and methane lifetimes contributing to a combined radiative effect of −60 mW m−2 (cooling). This cooling effect partially offsets the warming resulting from reduced BVOC-driven aerosol formation.
How to cite: Pozzer, A., Gromov, S., Nussbaumer, C., Stecher, L., Kohl, M., Ruhl, S., Tost, H., Lelieveld, J., and Vella, R.: Changes in global atmospheric oxidant chemistry from land cover conversion, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18698, https://doi.org/10.5194/egusphere-egu26-18698, 2026.
For decades, our understanding of the atmospheric distribution of ammonia has relied on a combination of in situ measurements, satellite remote sensing observations, and emission-driven atmospheric chemistry-transport model results. However, the limitations of these approaches, including sparse spatial distribution of in-situ measurements and underutilization of satellite data due to challenges in validating column observations against surface measurements, motivate further investigation of the global spatiotemporal variability of atmospheric ammonia. In this study, we jointly analyze observations from two well-validated infrared satellite instruments, IASI and CrIS, which provide near-global coverage and whose different overpass times (IASI at around 09:30 and CrIS at around 13:30 local time) yield complementary information on diurnal variability. We additionally examine the time-resolved ammonia concentrations from surface stations at selected locations within ammonia hotspot regions and assess how satellite observations compare over the same time frame. The results show that the magnitude of IASI-CrIS differences varies spatially. We investigate four factors that could impact the intercomparison -sensor sensitivity, seasonality, overpass time, and land-use characteristics- and find that their relative influence differs by location. At larger spatial scales, major global ammonia hotspots exhibit heterogeneous temporal behavior despite broadly consistent increasing decadal trends. Beyond these long-term trends, we investigate the seasonal variability of ammonia at the regional scale and examine how climatological and regional characteristics shape the observed patterns.
How to cite: Boufidou, F., Nüß, J. R., Shephard, M., Clarisse, L., Van Damme, M., Daskalakis, N., Vrekoussis, M., and Kanakidou, M.: Spatiotemporal variability of ammonia as observed from space: global patterns and regional insights from hotspots , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20533, https://doi.org/10.5194/egusphere-egu26-20533, 2026.
To gain a comprehensive understanding of the Earth’s climate system, it is essential to consider all the atmospheric gases with high global warming potential or substantial effects on the ozone layer. Besides CO2 and CH4, nitrous oxide (N2O) and halogenated carbon compounds—such as CFCs, HFCs, HCFCs, and PFCs—collectively classified as Other Long-Lived Greenhouse Gases (OLLGHGs), are particularly important due to their long atmospheric lifetimes and strong warming influence. In addition, nitrous oxide and chlorine-containing compounds are major contributors to anthropogenic ozone depletion.
The Long-Lived Greenhouse Gas Products Performance (LOLIPOP) Climate Change Initiative (CCI+) project, initiated by ESA in 2023, focuses on the OLLGHGs through the exploitation of multi-mission, satellite-based datasets. The main objective of the project is to assess whether the current suite of satellite observations is sufficiently robust for its use in climate science and climate services. If that is the case, the development of a harmonized and consistent dataset will be pursued in the future. Conversely, if limitations are identified, recommendations will be provided to improve the quality of satellite measurements of the OLLGHGs or to develop dedicated satellite missions for their monitoring.
Within the project, an inventory of available limb and nadir satellite datasets has been compiled for 11 OLLGHGs. Based on the outcomes of a literature review, the user needs (identified through a survey), and the dataset inventory, a subset of data has been selected for homogenization and intercomparison/validation exercises. The potentiality of satellite datasets for climate research and modeling is further demonstrated in the project through five test cases addressing the sensitivity of climate model simulations to OLLGHGs, including their radiative forcing, atmospheric lifetimes, and impacts on the stratosphere, such as effects on ozone recovery and atmospheric circulation. A growing community of scientific users is engaging with the project and has been involved in discussions on data quality and needs at a recent user workshop. Results from these studies, together with findings from the user needs survey and the dataset quality assessment, will be presented.
How to cite: Castelli, E. and the LOLIPOP team: Using satellite-based Other Long-Lived GHGs datasets for climate models applications and climate studies : The ESA LOLIPOP CCI project, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7520, https://doi.org/10.5194/egusphere-egu26-7520, 2026.
In a context of climate change and global warming, the characterisation and operational monitoring of greenhouse gases is of uppermost importance for implementing mitigation strategies that could help to reduce the impact of the current climatic emergency in the surrounding ecosystems and society. Among these gases, water vapour can contribute to almost a 60% of the total greenhouse effect. Moreover, its interaction with solar and infrared radiation or its main role in cloud formation, make water vapour a key driver of most atmospheric thermodynamic processes and a crucial component of the Earth's radiative budget.
Nevertheless, the large spatial and temporal variability of water vapour hinders the acquisition of reliable operational measurements. Remote sensing techniques such as the Global Navigation Satellite System (GNSS) have been proven to be an accurate and trustworthy alternative for integrated water vapour (IWV) retrievals, providing a valuable platform for continuous operational monitoring and thus enabling long-term characterisation. To further address this challenge, reanalysis data from Numerical Weather Prediction (NWP) models can significantly increase the temporal and spatial coverage of atmospheric variables datasets. In particular, ERA5 (fifth generation of European Centre for Medium-Range Weather Forecasts reanalysis) and MERRA-2 (Modern-Era Retrospective Analysis for Research and Applications, version 2) provide validated data for the city of Granada, in southeastern Spain, since 1980.
The current study presents a comprehensive analysis of IWV trends retrieved from a 15-year GNSS database and an extended 45-year reanalysis dataset. Special attention is paid to time-series quality control and homogenisation. Small jumps or discontinuities due to GPS receiver updates or changes in the data assimilation strategies of NWP models, can introduce artificial artifacts in the time series and consequently lead to biased or misleading trend esimates. A modified Mann-Kendall test proposed by Coen et al. (2020) that applies a Variance-Corrected Trend-Free Pre-Whitening approach is evaluated against a General Least Square method with a full custom covariance matrix accounting for residual heteroscedasticity and autocorrelation. While both methodologies agree on the sign and uncertainties of the retrieved trends, some discrepancies are found in the magnitudes, reflecting the different nature of both algorithms and highlighting the sensibility of trend detection techniques. Positive increasing IWV trends of a 3% per decade on average were obtained from both datasets and algorithms, being significant to a 95% level when analysing the 45-year time series. Nonetheless, relevant behaviour differences are found between the 1980-2000 and 2000-2024 periods, unveiling the pronounced increasing in IWV experimented during the last 25 years. The results obtained are consistent with previous studies, both regarding the trend magnitude and the uncertainty range, reinforcing the capability of the GNSS technique and NWP models as robust tools for environmental and atmospheric monitoring of complex variables such as water vapour (Parracho et al., 2018; Yuan et al., 2023). However, they also unveil trend discrepancies which are inherent to the chosen retrieval methodologies and that must always be assessed.
How to cite: Naval Hernández, V. M., Díaz Zurita, A., Rodríguez Navarro, O., Muñiz Rosado, J., Pérez Ramírez, D., Whiteman, D. N., Alados Arboledas, L., and Navas Guzmán, F.: Integrated Water Vapour (IWV) trend analysis from GNSS and NWP reanalyses: a homogenised long-term analysis over Granada, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12375, https://doi.org/10.5194/egusphere-egu26-12375, 2026.
We present seasonal post Hunga-Tonga measurements (2023-2025) of upper tropospheric and lower stratospheric water vapor over the Alpine region, obtained from deployments of balloon-borne frost point hygrometers within the Swiss H2O Hub, a consortium dedicated to water vapor measurements from ground to space. The chilled mirror hygrometers consist of the CFH (Cryogenic Frostpoint Hygrometer) instrument with classical cryogen, as well as two low global warming potential instruments: CFH-DIA (CFH using a mixture of dry ice and alcohol) and PCFH (Peltier Cooled Frostpoint Hygrometer).
The CFH measurements compare well to collocated space-borne Aura/MLS H2O retrievals, confirming the increased water vapor content in the lower stratosphere after the Hunga-Tonga eruption, with MLS being on average drier than the CFH reference by about 0.1-0.3 ppmv at around 20 km altitude over Switzerland. Starting May 2024, the temporal availability of MLS H2O observations decreased to around one week per month, due to the duty-cycling of the MLS 190 GHz receiver, in order to extend its lifespan.
We find that, despite a reduced cooling power (which is governed by the sublimation of CO2), CFH-DIA can be used as alternative reference to CFH for the Swiss H2O Hub, with a residual risk of losing frost control in certain atmospheric situations (e.g., when the 2nd cleaning cycle of CFH-DIA occurs above the tropopause).
The PCFH instrument uses thermoelectric cooling with custom-made heat sinks. It has undergone important design revisions through 2023-2025, improving heat dissipation, the quality of the optical signal, and controller operation. We find that the redesigned instrument is able to provide atmospheric dew or frost point measurements from the ground up to at least 23 km, with little preparation efforts due to a fully-electric design.
These new developments in chilled mirror hygrometry pave the way for environmentally friendly, high accuracy, and high vertical resolution observations of water vapor in the UTLS.
How to cite: Poltera, Y., Wienhold, F. G., Artho, V., Brossi, S., Brossi, T., Brunamonti, S., Romanens, G., Brun, A., Luo, B., Peter, T., and Stober, G.: Observations of post Hunga-Tonga UTLS water vapor over the Alpine region with balloon-borne low-GWP frost point hygrometers, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14905, https://doi.org/10.5194/egusphere-egu26-14905, 2026.
This paper highlights the main findings of the twenty-first annual Greenhouse Gas Bulletin (https://library.wmo.int/idurl/4/69654) 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/site/knowledge-hub/programmes-and-initiatives/global-atmosphere-watch-programme-gaw).
The Bulletin presents global analyses of observational data collected according to GAW recommended practices (https://library.wmo.int/idurl/4/69672) 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 179 marine and terrestrial sites for CO2, 171 for CH4 and 123 for N2O. The globally averaged surface mole fractions calculated on the basis of these observations reached new highs in 2024, with CO2 at 423.9±0.2 ppm, CH4 at 1942±2 ppb and N2O at 338.0±0.1 ppb. These values constitute, respectively, 152%, 266% and 125% of pre-industrial (before 1750) levels. The record increase in CO2 from 2023 to 2024 (3.5 ppm) was most likely due to a combination of natural variability and continued emissions of fossil fuel CO2. For CH4, the increase from 2023 to 2024 was lower than that observed from 2022 to 2023 and also lower than the average annual growth rate over the last decade (2014–2023). For N2O, the increase from 2023 to 2024 was lower than that observed from 2022 to 2023 and slightly lower than the average annual growth rate over the last decade.
The increase of CO2 in the global surface atmosphere by 3.5 ppm in 2024 was the largest one-year increase in the modern measurement record, exceeding the previous record of 3.3 ppm from 2015 to 2016 and surpassing the increase of 2.4 ppm from 2022 to 2023 by a large margin. Global fossil CO2 emissions were almost static during 2023–2024 at the record level of 10.2 ± 0.5 GtC/yr. The global terrestrial ecosystems and global oceans are likely responsible for the additional 1.1 ppm/yr (equivalent to 2.34 GtC) in CO2 growth compared to 2022–2023. Wildfire emissions in the Americas reached historic levels in 2024 and could have contributed to the record CO2 annual increase.
Current CO2 emissions to the atmosphere not only impact the global climate today but will continue to do so for millennia, and ongoing CO2 emissions will ensure that warming continues indefinitely. The removal of anthropogenic CO2 from the atmosphere depends on exchanges among reservoirs on timescales ranging from years (surface ocean) to hundreds of thousands of years (weathering). The slowed uptake of anthropogenic CO2 emissions within the global carbon cycle is exacerbated by the slow uptake of heat by the deep oceans, so once CO2 is emitted to the atmosphere, it affects climate indefinitely. This is different from CH4, whose atmospheric lifetime is about nine years due to its removal by chemical oxidation. While reducing CH4 emissions is useful and necessary, climate action urgently needs to focus on reducing fossil fuel CO2 emissions, which represent the vast majority of overall greenhouse gas emissions.
How to cite: Tarasova, O., Lan, X., Chen, H., Vermeulen, A., and Tsuboi, K.: The state of greenhouse gases in the atmosphere using global observations through 2024, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10902, https://doi.org/10.5194/egusphere-egu26-10902, 2026.
Atmospheric methane (CH4) is a key short-lived climate forcer whose concentration has increased rapidly over the last two decades, yet important uncertainties remain regarding its regional-scale evolution and its relationship to reported anthropogenic emissions. In particular, Eastern Europe remains comparatively underrepresented in regional methane assessments based on consistent long-term datasets. In this study, we investigate recent methane trends at global, European and national (Romania) scales by combining atmospheric reanalysis products, surface observations and emission inventories.
Near-surface methane concentrations are analysed using the Copernicus Atmosphere Monitoring Service (CAMS) global greenhouse gas reanalysis for the period 2003–2022. Regional mean time series are derived for Europe and Romania and compared to the global mean methane evolution obtained from NOAA surface observations. To provide a bottom-up perspective, anthropogenic methane emissions are analysed using the EDGAR inventory, with a focus on national and sectoral contributions relevant for Romania. The consistency between atmospheric concentration trends and reported emission changes is assessed across spatial scales.
The study provides new insight into the regional behaviour of atmospheric methane in Eastern Europe and contributes to the ongoing evaluation of methane mitigation efforts at European and national levels. The value of combining reanalysis products, observational datasets and emission inventories to characterise methane trends from global to national scales is also shown.
How to cite: Scarlat, A., Tudor, A., and Iorga, G.: Atmospheric drivers of climate change over Romania with focus on CH4: sources and changes inferred from reanalysis, observations, and emission inventories, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6307, https://doi.org/10.5194/egusphere-egu26-6307, 2026.
Methane is the second most important anthropogenic greenhouse gas. Since 2007, atmospheric methane concentrations have resumed growth following a period of relative stabilization, with the growth rate accelerating in recent years. At the same time, a reversal in the isotopic trend of atmospheric methane suggests possible changes in sources driving the observed increase in atmospheric CH₄.
In this study, we use a novel approach based on the Miller-Tans method, which uses short-term devations from a smooth background signal in observed time series of CH4 mole fraction and isotopic composition to infer δ¹³C-CH₄ source signatures of this short-term component. This allows us to focus on regional scale changes in methane sources .
We use 20 years of long-term atmospheric methane and carbon isotope (δ¹³C-CH₄) observations from a global sampling network to conduct a comprehensive analysis of the spatial distribution, seasonal variability, and long-term trends of δ¹³C-CH₄ source signatures. In particular, we observe a pronounced decrease in δ¹³C-CH₄ source signatures at high northern latitudes after 2007, indicating a relative increase in isotopically depleted, biogenic methane sources in this region. By comparing our observation-based results with inverse modeling studies, we further discuss how this regional shift is reflected at the global scale and explore possible explanations underlying the substantial shifts in the source mix at high northern latitudes.
How to cite: Yu, X., Dasgupta, B., Michel, S. E., Miller, J. B., Lan, X., Basu, S., Morimoto, S., Fujita, R., Goto, D., and Röckmann, T.: Changes in methane source signatures inferred from long-term CH₄ and δ¹³C-CH₄ observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19412, https://doi.org/10.5194/egusphere-egu26-19412, 2026.
Understanding the drivers of atmospheric CH₄ variability requires separating emission changes from sink perturbations—a challenge that arises when either alter CH₄ concentrations. Stable isotopes (δ¹³C, δD) provide additional constraints because sources have distinct signatures, while sinks fractionate isotopes through kinetic isotope effects (KIEs). We use complementary two-box modelling approaches to quantify how isotopes respond when CH₄ observations alone cannot distinguish mechanisms.
Our forward model simulates the evolution of hemispheric CH₄, ¹³CH₄, and CH₃D, where emissions add mass with source-specific signatures (thermogenic, biogenic, and pyrogenic), chemical sinks (OH, stratosphere, and soil) remove mass and accordingly fractionate isotopes, and interhemispheric mixing transfers methane across hemispheres. During spin-up, baseline emissions balance removal, yielding steady-state atmospheric isotopic trajectories.
Following the equilibrium period in the spin-up, we enforce OH perturbation, where we impose emission compensation to hold CH₄ constant while varying OH trends (-1.0 to +1.0%/yr). Four compensation strategies, proportional (maintains baseline mix), microbial-dominated, fossil-dominated, and pyrogenic-dominated, produce different isotopic trajectories despite identical CH₄ evolution. For +1.0%/yr OH, Northern Hemisphere δ¹³C shifts range from -3.7‰ (microbial compensation, depleted sources balance enriched removal) to +3.3‰ (pyrogenic compensation, enriched sources overcompensate). Isotopic phase-space analysis reveals cumulative compensation masses of 1200-1900 Tg over 45 years, with δD providing orthogonal constraints (Δδ¹³C/ΔδD slopes distinguish microbial vs thermogenic sources). Forward simulations without compensation show transient isotope responses with ~8-year relaxation timescales, demonstrating that observed 2000-2006 methane stabilization (δ¹³C flattening at ~-47.3‰) requires near-cancellation of source and sink trends. Our dual-isotope framework demonstrates that atmospheric composition networks can attribute decadal CH₄ variability to specific emission sectors even when concentration trends vary, critical for verifying bottom-up inventories and climate-policy targets.
How to cite: Dasgupta, B., Yu, X., and Röckmann, T.: Disentangling Source and Sink Contributions to Atmospheric Methane Isotope Evolution: Insights from Two-Box Model Experiments, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20940, https://doi.org/10.5194/egusphere-egu26-20940, 2026.
Methane (CH4) is a potent greenhouse gas, contributing approximately 25% of anthropogenic warming since pre-industrial times. Recent years have seen a rapid, largely unexplained acceleration in its atmospheric growth rate, with record increases during 2020–2022. While prevailing research focuses on surface emissions and tropospheric sinks, the influence of the stratosphere remains largely treated as a static boundary condition. Here, we present observational evidence of stratospheric impacts that shows critical yet underexplored factors affecting atmospheric methane growth. These findings suggest that natural variability in stratospheric dynamics is a significant, yet overlooked, driver of the global methane budget, with implications for attribution studies and climate projections.
How to cite: Yin, Y., Nguyen, N., Wang, Q., Turner, A., Chevallier, F., and Frankenberg, C.: Natural Variability in Stratosphere-Troposphere Exchange: An Underappreciated Driver of Global Methane Growth Rates, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21945, https://doi.org/10.5194/egusphere-egu26-21945, 2026.
Atmospheric carbon dioxide (CO₂) and its stable carbon isotope composition (δ¹³C) provide important constraints on CO₂ sources and sinks; however, long-term high-frequency observations remain limited in East Asia.
This study presents continuous observations of atmospheric CO₂ and δ¹³CO₂ obtained at the Gosan station on Jeju Island, South Korea, from 2017 to 2025 using a cavity ring-down spectroscopy (CRDS) analyzer. The 9-year record is based on 1 Hz measurements aggregated into hourly mean values, with measurement precisions of 0.01 ppm for CO₂ and 0.05‰ for δ¹³CO₂.
The observations reveal pronounced seasonal cycles in both CO₂ and δ¹³CO₂, with mean seasonal amplitudes of approximately 8–10 ppm for CO₂ and 0.4–0.5 ‰ for δ¹³CO₂, exceeding those observed at global background sites and reflecting the continental–marine boundary characteristics of the Gosan station. From 2017 to 2021, both the CO₂ growth rate and the long-term decline in δ¹³CO₂ are broadly consistent with global background trends, whereas after 2022, notable deviations from global background behavior are observed in both CO₂ growth rates and δ¹³CO₂ trends. Superimposed on these background variations, pollution-influenced air masses exhibit pronounced changes in δ¹³CO₂. Yearly Keeling plot analysis of CO₂–δ¹³CO₂ relationships for pollution events indicates a progressive enrichment in isotopic source signatures over time, suggesting a temporal shift in dominant emission sources.
To investigate anthropogenic source characteristics associated with these pollution signals, high-CO₂ events are first classified based on air mass transport pathways, and further examined by incorporating high-frequency measurements of carbon monoxide (CO) and nitrous oxide (N₂O) provided by the National Institute of Meteorological Sciences (NIMS), which serve as complementary tracers of combustion-related and non-combustion emission influences, respectively.
How to cite: Jang, J., Kim, J., Choi, H., Choi, J., Yun, J., Jang, J., Kim, S., Shin, D., Yang, S., and Park, S.: Long-Term High-Frequency Measurements of Atmospheric CO₂ and δ¹³CO₂ at Gosan: Implications for Source Characteristics in East Asia, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8986, https://doi.org/10.5194/egusphere-egu26-8986, 2026.
Long term trends in greenhouse and reactive gases highlight changes in the atmospheric background (AB) and help determining the impact of anthropogenic emissions. The presence of pollution events calls for the implementation of background detection methods, capable of differentiating the AB from fresh anthropogenic emissions. At the Mauna Loa observatory (MLO) operated by NOAA, ad hoc procedures are applied to measurements in order to filter out pollution events and sinks from the AB of key gases such as carbon dioxide (CO2) and methane (CH4). These procedures account for MLO’s known sources and sinks in the area, and its location.
At the Lamezia Terme (LMT) observation site in Calabria, Southern Italy, part of the WMO/GAW network, several methods have been implemented to filter out non-AB measurements of carbon monoxide (CO), CO2, and CH4. Namely, the BaDS (Background Data Selection), SM (Smoothed Minima), Wind, and the ONRPI (Ozone to Nitrogen Oxides Ratio Proximity Indicator). While the Wind method is based on an algorithm specifically designed to consider LMT’s characteristics as a central Mediterranean site, BaDS and SM were already present in literature and their implementation at LMT involved minor changes. These methods are statistical in nature, while the ONRPI is based on atmospheric chemistry, i.e. the O3/NOx ratio. The ONRPI classifies as BKG (Background) data with a O3/NOx ratio higher than 100, attributed to very aged air masses. Multiple studies on LMT’s record of greenhouse and reactive gases, as well as aerosols, have expanded the ONRPI and turned LMT into a key hotspot for the implementation of this methodology and its correction factors.
The performance of BaDS, SM, and Wind on the LMT record of CO, CO2, and CH4 has been assessed using nearly a decade of continuous measurements, however no attempts have been made to compare these methods with the ONRPI. A direct comparison between the ONRPI and other methodologies has highlighted the presence of data in the LMT record attributed by BaDS, SM, and Wind to the AB of CO, CO2, and CH4, which are however characterized by very low O3/NOx ratios and therefore affected by local sources of emissions. For example, up to 49.79% of the data classified as URB (Urban, with O3/NOx ratio lower than 0.1) by the ONRPI, are flagged by BaDS as representative of CO’s AB. Consequently, the AB itself tends to be overestimated.
A multi-year analysis applied to nearly one decade of continuous measurements at LMT, integrated by statistical evaluations, has shown substantial differences between the seasonal oscillations and annual growth rates of CO2 and CH4 as computed by the ONRPI, and those resulting from the other methods. During the boreal summer, the AB of CO filtered by ONRPI is nearly 20% lower than that of the other methods, possibly due to contributions such as Mediterranean open fires which are not filtered out by BaDS, SM, and Wind. While these comparisons need to be further expanded, the findings underline the importance of integrating multiple methodologies for AB detection.
How to cite: D'Amico, F., Lo Feudo, T., Ammoscato, I., Gullì, D., De Pino, M., and Calidonna, C. R.: Preliminary results from the direct comparison of four atmospheric background detection methods at a central Mediterranean WMO/GAW station: potential implications for long-term CO, CO2, and CH4 monitoring, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11870, https://doi.org/10.5194/egusphere-egu26-11870, 2026.
Climate modeling studies predict a strengthening of the Brewer Dobson Circulation, which has implications for global atmospheric composition, radiation, and climate. This predicted acceleration has not been confirmed with observations, and models also disagree about the mean stratospheric circulation and mixing strength. In previous work, we developed a long record of mean age of air from an N2O combined satellite product – part of the Stratospheric Water and OzOne Satellite Homogenized (SWOOSH) package – by inferring age from latitude-dependent Age:N2O relationships. While SWOOSH corrects for the drift in Microwave Limb Sounder (MLS) N2O measurements, positive trends in derived mean ages over the past two decades based on these fixed Age:N2O relationships are in contrast to mean age trends derived from Atmospheric Chemistry Experiment (ACE) SF6 and in situ measurements. This contrast in mean age trends confirms the changes of the in-situ Age:N2O relationship over time and indicates a need to have both latitude and time varying Age:N2O relationships for more accurate age derivations. Using time-varying Age:N2O relationships, we introduce an N2O-derived mean age product that now addresses 1) biases in satellite N2O observations and 2) the positive N2O-age trends. In addition, we compare our results with previous mean age trend analyses to determine if the corrections are robust, which will further contribute to understanding long-term circulation and mixing variability based on observed trace gas trends.
How to cite: Castillo, A., Ray, E., Saunders, L., and Linz, M.: Mean Stratospheric Age of Air from Satellite Observations of N2O and Tracer Correlations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14717, https://doi.org/10.5194/egusphere-egu26-14717, 2026.
Nitrous oxide (N2O) is the third most important long-lived greenhouse gas and the most dominant contributor to stratospheric ozone depletion. In Germany, long-term atmospheric N2O mole fractions are measured continuously at two background stations: Schauinsland (47°55‘N, 7°55‘E, 1205 m above sea level) and Zugspitze (47°25‘N, 10°58‘E, 2656 m above sea level). In this study, high-resolution measurements from 2001 (Schauinsland) and 2003 (Zugspitze) to 2024 were subjected to a comprehensive quality control process, including consistency checks and filtering to reduce the influence of local sources.
The long-term trends of N2O mole fractions at Schauinsland and Zugspitze stations, of 0.82 ppb/yr and 0.85 ppb/yr, respectively, agree well with the marine background observations from the AGAGE at Mace Head station, and with global tropospheric growth rates. The continental excess during the last 25 years was found to be 0.9 ppb at Schauinsland and 0.5 ppb at Zugspitze. At Schauinsland station, the amplitude of the seasonal cycle decreased from 1.0 ppb during 2001-2010 to 0.7 ppb during 2011-2024. The diurnal variability ranges from 0.1 ppb in winter to 1.0 ppb in summer. At Zugspitze, the annual variability is 0.4 ppb. The amplitudes in the mean diurnal cycle range from 0.03 ppb during the winter months to 0.15 ppb during summer months. Regional N2O emissions in the vicinity of Schauinsland (Upper Rhine Valley) were quantified using the radon tracer method, based on 222Rn activity measurements provided by the German Federal Office for Radiation Protection. The derived N2O fluxes from the radon tracer method were extrapolated to annual emissions and compared with different emission inventories (EDGAR, UNFCCC, and E-PRTR/IREP), focusing particularly on the differences between the inventories regarding emissions attributed to the chemical industry in the Alsace region of France.
How to cite: Reith, S. J. E., Couret, C., Großmann, J., Meinhardt, F., Schmid, S., and Schmidt, M.: Atmospheric N2O trends, variability, and regional emissions derived from long-term observations and the radon tracer method at Schauinsland and Zugspitze stations (Germany), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17700, https://doi.org/10.5194/egusphere-egu26-17700, 2026.
The Scripps Pier (Scripps Institution of Oceanography) is one of the few sites globally with concurrent, continuous, in situ measurements of atmospheric O2 and CO2. Situated at a land ocean interface near a dense urban corridor, the site receives marine and continental air masses under transport conditions shaped by land sea breezes, boundary layer evolution, productive coastal waters, terrestrial biosphere and local fossil fuel fluxes. We find that variations of atmospheric O2 and CO2 were largely anticorrelated, but shifted in phase, a pattern consistent with opposite-sign responses to surface exchange processes and to modulation by atmospheric transport. Diurnal phase space relationships between O2 and CO2 often form closed loop structures that emerge from phase offsets between surface fluxes and transport pathways. The detailed structure of these phase relationships varied from day to day with changes in wind regimes and with varying contributions from urban fossil fuel emissions, terrestrial biosphere exchange, and air-sea fluxes. Back trajectory classification resolved these relationships into nocturnal offshore and daytime onshore flows with distinct O2 to CO2 slopes that indicated differing mixtures of the contributing processes. Many features of the observed patterns can be understood based on day-to-day variation of the relative amounts of different processes with fixed exchange ratios. This study also addresses the extent to which episodic variability in oceanic dissolved oxygen influences atmospheric O2 variability at the site.
How to cite: Sardarli, M., Mühle, J., Morgan, E. J., Paplawsky, B., Walker, S., Kim, J., Lueker, T., and Keeling, R. F.: Insights from Diurnal Cycle of O2 and CO2 Records Collected at Scripps Pier, La Jolla, California, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15583, https://doi.org/10.5194/egusphere-egu26-15583, 2026.
The Montreal Protocol (1989) is widely regarded as one of the most successful environmental agreements, having phased down ozone-depleting substances such as chlorofluorocarbons (CFCs), followed by hydrofluorocarbons (HCFCs) in 2013 and hydrofluorocarbons (HFCs) in 2019. Today, developed countries primarily use hydrofluoroolefins (HFOs) as fourth-generation replacements. A key factor in this success is continuous global monitoring of these compounds. The Scientific Assessment of Ozone Depletion, published every four years, lists over 780 substances with their ozone-depleting potential (ODP) and global warming potential (GWP). However, fewer than 10% (~70) have quantified atmospheric abundances, primarily measured by the Ad-vanced Global Atmospheric Gases Experiment (AGAGE) network using cryogenic pre-concentration (Medusa) coupled with gas chromatography quadrupole mass spectrometry (GC–qMS).
As the number of regulated and unregulated compounds grows, comprehensive detection is essential. Quadrupole MS limits ion coverage, prompting the development of a non-target screening (NTS) approach. We combine an advanced preconcentration unit (Aprecon), GC-time-of-flight MS, and the ALPINAC algorithm for automated fragment formula annotation. This workflow has identified more than 80 previously unidentified persistent halogenated compounds in routine air samples.
To support global research efforts, we provide a suspect screening list of atmospheric compounds of concern, including mass fragments and retention time indices. High-resolution mass spectra are shared via Mass Bank, including data for compounds lacking publicly available spectra. This resource enhances the identification and monitoring of emerging halogenated substances, strengthening global capacity to track and mitigate their environmental impact.
How to cite: Constantin, L., Begley, A., Augugliaro, M., Schneider, L., Vollmer, M., and Stefan, R.: Expanding Atmospheric Surveillance: Non-Target Screening and Open Spectral Databases for Persistent Halogenated Compounds, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10456, https://doi.org/10.5194/egusphere-egu26-10456, 2026.
Industrial compounds that contain halogens are potent greenhouse gases, and those that contain chlorine and bromine substantially reduce springtime ozone over the poles. As a result, these gases have been phased out by the 1987 Montreal Protocol and its subsequent amendments. However, many persist in the atmosphere due to their long lifetimes and gradual elimination from industry. Chlorofluorocarbons (CFCs) and carbon tetrachloride (CCl4) were scheduled to be fully phased out by 2010 and replaced by hydrochlorofluorocarbons (HCFCs), which will be banned worldwide by 2030. Some halogenated gases, such as perfluorocarbons (PFCs), have global warming potentials thousands of times greater than carbon dioxide but are not controlled by the Montreal Protocol or any other agreement. With so many halogen-containing compounds remaining in the atmosphere at different levels of regulation, it is crucial to continue carefully monitoring their abundances and trends. This can be accomplished using global satellite-based measurements, which have been continuously available for many of these gases as of the early 2000s. To maximize the reliability of these measurements, it is important to validate them through comparisons with other observations. In this study, we compare collocated measurements from three different satellite instruments (ACE-FTS on SCISAT, HIRDLS on Aura, and MIPAS on Envisat) with each other and with independent reference data from balloon-based instruments for CFC-11, CFC-12, CFC-113, HCFC-22, CCl4, and CF4. We find that overall, the satellite instruments perform well, but for certain regions and time periods, there are significant biases that need to be considered throughout any monitoring activities.
How to cite: Walker, K. A., Saunders, L. N., Stiller, G. P., Raspollini, P., Kolonjari, F., Jalali, A., Millán, L. F., Wetzel, G., and Toon, G. C.: Evaluating satellite-based measurements of halogenated gases, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15075, https://doi.org/10.5194/egusphere-egu26-15075, 2026.
Why AC2E?
The AC2E initiative is based on several comments from scientists working in the MLT region regarding the potential impact from re-entering space debris burning up in the mesosphere. Furthermore, increasing numbers of orbital launches might have exhaust effects on the MLT region.
The initiative will focus on the possible impacts caused by the emerging large constellations of satellites. Hence, it’s of vital importance to start a monitoring program as early as possible to secure baseline data before too many constellations are in orbit and the re-entering mass increases exponentially.
The mesosphere is sometimes referred to as the "new ocean" since in earlier times, people considered items dropped into the ocean as something they didn’t need to worry about anymore. It “disappeared”. These days we know much better.
Only in January 2025, 120 Starlink satellites burnt in the atmosphere. According to an ESA report, in 2022, more than 200 tons of metal particles were introduced into the atmosphere, in 2024, it was already 800 tons. Until 2040, more than 60.000 new satellites are predicted to be launched into orbit. This might lead to the disposal of up to 10.000 tons of Al2O3 / year into the atmosphere. Especially the upper atmosphere is very vulnerable for two reasons. Due to its low density, mass contribution has a much bigger effect. 1 ton of material in the MLT region equals up to 100.000 tons in the troposphere.
What is AC2E?
The “AC2E” is an international collaboration effort targeting advancement in specific, fundamental issues in space and earth science. The concept was conceived and developed between 2024 and 2026 by Andøya Space (ASP), Esrange/SSC and DLR MORABA.
The main aim for AC2E is to set up a repetitive monitoring program providing measurements in the Mesosphere / Lower Thermosphere (M/LT) at regular intervals by any means possible, but in a systematic and standardized way. Thus, providing regulatory bodies with relevant background information for decision making.
The projected timeframe of 2027 to 2037 is specifically chosen to align the initiative with the upcoming Solar Cycles 26 and 27, which have a large influence on the dimensions and characteristics of Earth’s atmosphere and its interaction with space objects. Such background information must be based on as much pristine and unmodified data as possible.
Possible science topics
Atmospheric Pollution from Re-entry: As satellites demise, they burn up and release materials (e.g., aluminum, titanium, composites) into the MLT. Sounding rockets equipped with sensitive instruments can:
· Identify and quantify new types of artificial aerosol layers resulting from satellite re-entry.
· Investigate the chemical reactions of these materials with the ambient atmospheric constituents.
· Assess the potential impact on natural metal layers and MLT chemistry, including ozone.
Influence on NLCs/PMCs
Localized Atmospheric Perturbations
Impacts of Orbital Rocket Launches
How to cite: Blix, K., Schoppmann, K., Hörschgen-Eggers, M., Kirchhartz, R., Abrahamsson, M., and Andersson, K.: Atmospheric Composition in the Constellation Era – The AC2E Initiative (2027 – 2037), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2678, https://doi.org/10.5194/egusphere-egu26-2678, 2026.
Austral spring (September–November) represents the season with the most pronounced chemical depletion of stratospheric ozone over Antarctica, during which the associated radiative and circulation responses reach their annual maximum. Against the background of persistently low Antarctic sea ice, this study focuses on austral spring and examines the influence of stratospheric ozone variability on Antarctic sea ice through both thermodynamic and dynamic processes. The analysis is based on simulations from the Whole Atmosphere Community Climate Model version 6 (WACCM6), combined with composite analysis and other statistical methods, to investigate the interannual variability of Antarctic springtime stratospheric ozone and its impacts on sea ice.The results indicate that WACCM6 successfully reproduces the interannual variability of Antarctic spring total column ozone (TCO), with simulated TCO variations consistent with those derived from the SWOOSH and Microwave Limb Sounder (MLS) observational datasets. Composite analyses show that ozone-related anomalies in Antarctic spring sea ice concentration are primarily confined to the seasonal ice zone between 60°S and 70°S, with magnitudes reaching ±5%–20%. During years of anomalously high springtime stratospheric ozone, sea ice concentration over the Amundsen and Bellingshausen Seas (ABS; 60°S–70°S) exhibits significant negative anomalies, indicating a marked reduction of sea ice along the ice-edge region. Thermodynamic analysis reveals that elevated springtime stratospheric ozone is associated with pronounced positive anomalies in sea surface temperature and surface net radiation over the ABS ice-edge zone, with magnitudes of approximately +1–3 °C and +5–15 W m⁻², respectively. The enhanced radiative heating leads to substantial near-surface warming, thereby suppressing sea ice formation and accelerating ice-edge melt. Further analysis of the dynamical processes shows that increased absorption of shortwave radiation by ozone induces warming in the high-latitude stratosphere, accompanied by rising geopotential heights and a weakened meridional temperature gradient. As a result, high-latitude stratospheric westerlies weaken and the polar vortex intensity decreases. These stratospheric circulation anomalies subsequently propagate downward and modify near-surface wind stress patterns, creating wind forcing favorable for Ekman pumping in the ice-edge region. The enhanced upwelling of subsurface warm water ultimately contributes to reduced sea ice concentration along the Antarctic seasonal ice zone.
How to cite: Shujie, C., zhenfeng, C., Wuhu, F., Ren, C., Ting, X., and Haotian, H.: Impacts of Stratospheric Ozone on Antarctic Spring Sea Ice: Based on WACCM6 , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4836, https://doi.org/10.5194/egusphere-egu26-4836, 2026.
The recovery of Arctic ozone has become an increasingly important indicator of the effectiveness of global policies regulating ozone-depleting substances. While severe ozone depletion first emerged over Antarctica in the late 1970s and reached its maximum in the late 1980s, Antarctic ozone has exhibited clear recovery since the early 2000s. In contrast, long-term ozone trends in the Arctic have remained uncertain due to strong dynamical variability. In this study, we investigate Arctic ozone changes from 1988 to 2024 using a comprehensive set of observations, including satellite datasets, ozonesondes, reanalysis products, and ground-based measurements. Our analysis reveals statistically significant positive trends in upper-stratospheric ozone (3–1 hPa), reaching up to 0.915 ± 0.251% per decade, based on the Stratospheric Water and Ozone Satellite Homogenized (SWOOSH) and merged satellite records (SAGE-CCI-OMPS). Total column ozone (TCO) also exhibits a significant increase during 2000–2024, with trends of 8.51 ± 6.03 DU/dec from merged satellite (MSAT) records and 6.51 ± 3.88 DU/dec from ground-based observations. Seasonal analysis of combined station data reveals robust positive trends in the southern Arctic (Lerwick, Scoresbysund, Sodankylä, Oslo) during autumn (9.11 ± 2.38 DU/dec) and spring (6.24 ± 4.71 DU/dec), while the other seasons exhibit weak but positive trends. Although the extreme Arctic ozone depletion event of 2020 influences trend estimates across different post-2000 periods. Nevertheless, all stations exhibit positive TCO trends from 2000 to 2024, providing strong evidence that Arctic ozone is undergoing recovery.
How to cite: Sathyanath, A. and Kuttippurath, J.: Tracing the emerging Recovery Signals of Arctic Stratospheric Ozone, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16273, https://doi.org/10.5194/egusphere-egu26-16273, 2026.
The recovery of the stratospheric ozone layer faces increasing challenges from the rising emissions of unregulated very short-lived substances (VSLS). While the rapid increase in chlorinated VSLS, particularly dichloromethane (DCM), has been considered as a measurable threat to ozone recovery timelines, the potential risks posed by iodinated alternatives remain under-characterized. Although iodine emissions are largely natural, climate change may lead to a change in source strength. It is also important to quantify the impact of any possible anthropogenic sources. Finally, the interaction of iodine with other (decreasing) halogens may affect the efficiency of some chemical ozone loss mechanisms.
We investigate the potential impact on the stratospheric ozone layer of the several emission scenarios of iodinated VSLS. Model sensitivity experiments with a global 3-D chemical transport model TOMCAT show a strong dependence of ozone depletion on emission locations. Emissions in the wider tropics, or localised in southeastern Asia, give depletion 4-6 times that from emission in the mid-latitudes of the northern hemisphere. We will show ozone responses to the emissions in terms of polar ozone loss, and global total column trends. We will present our results in terms of ozone depletion potential (ODP) and a new metric, integrated ozone depletion (IOD). We will compare the results for iodine with the widely discussed chlorinated VSLS, DCM, and the long-lived ozone-depleting substance, CFC-11.
How to cite: Wang, Z. and Chipperfield, M.: Impacts of Iodinated Very Short-Lived Substances on Stratospheric Ozone, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21403, https://doi.org/10.5194/egusphere-egu26-21403, 2026.
The recovery of the ozone layer is expected by the middle of the 21st century, after the significant depletion detected during the 1980s. However, confirming this recovery critically relies on high-quality and long-term measurements, which play a key role in monitoring changes in atmospheric constituents and in detecting global trends.
Here we present the homogenised ozone time series of Arosa/Davos. This time series is based on measurements performed by Dobson and Brewer spectroradiometers covering the period from 1926 to the present and constitutes the world’s longest continuous ground-based ozone dataset. This study focuses on the 1990 to 2024 period and the eventual recovery of ozone after the international efforts to reduce the chlorofluorocarbons emissions. We use the merged ozone times series of Arosa/Davos composed of three Brewer and three automated Dobson spectroradiometers data records. To reconcile the seasonal discrepancies between the Brewer and the Dobson dataset, we followed the methodology explained in previous studies. The improvements employed includes replacing the operational ozone absorption cross-section (Bass and Paur, 1985) with the measured by the University of Bremen (Serdyuchenko et al., 2014) and correcting the ozone effective temperature using the ozone sondes measurements from Payerne. Furthermore, the measurement uncertainty was derived for each of the six instruments to produce homogenised merged ozone dataset.
The relocation of the instruments from Arosa to Davos during the period 2011-2021 was carefully analysed and allowed the determination of a constant transfer factor to ensure homogeneity of total column ozone between both sites. This factor was found to be equal to the climatological tropospheric ozone column differences. Finally, the datasets from all instruments were merged to combine one consistent single record.
The robustness of this merged ozone time series should enable the detection of an ozone recovery signal, by reducing the possibility of misinterpretation due to instrumental artefacts. As a future work, we will aim to assess long-term ozone changes and evaluated the attribution of the stratospheric and tropospheric ozone from the potential recovery detection of this homogenised time series.
How to cite: Cabello, F., Gröbner, J., Egli, L., Zeilinger, F., Maillard Barras, E., Ruefenacht, R., and Stober, G.: Setting the path for evaluating ozone recovery in the Alps using a homogenised long-term ground-based ozone time series., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4020, https://doi.org/10.5194/egusphere-egu26-4020, 2026.
The Perseverance is a sailboat belonging to the "Polar Ocean" association, headed by Jean-Louis and Elsa Etienne. This vessel carries several scientific instruments, including five atmospheric measurement systems monitoring gaseous mercury, ozone, nitrogen oxides, radon, and a laser particle counter. Over the past six months, the ship departed Nice, France, in the Mediterranean Sea, crossed the Strait of Gibraltar and the North Atlantic to reach Nuuk, Greenland. The second leg took the ship from Nuuk to San Francisco, via the Northwest Passage and the Bering Strait. The third leg took the ship along the Mexican coast, to Clipperton Atoll, Papeete, Tahiti, and Christchurch, New Zealand. Atmospheric quality was continuously monitored during this period, and we will present the combined variations of these five parameters in space and time variabilities. As expected, pollution is highest in ports and decreases during the passage from the Atlantic to the Pacific, with a further decrease upon entering the Southern Hemisphere.
The Atmobox onboard system also has the unique feature of transmitting its data in real time for long term experiments, thus allowing its operation to be monitored by a team of scientists on Earth when there are no qualified personnel on board.
Aknowledgements: Jean Louis and Elsa Etienne head of the association "Océan Polaire" leadind the Persévérance.
How to cite: Losno, R., Colomb, A., Fourquez, M., Bouatir, F.-E., Knoery, J., Le Goff, H., Garçon, V., and Boye, M.: AtmoBox, a real time device to measure atmospheric pollutants on board of Perseverance: transoceanic and polar cruises, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21260, https://doi.org/10.5194/egusphere-egu26-21260, 2026.
Long-term measurements of aerosol particles and trace gases are available from several well-equipped research stations in Europe and North America, but global coverage of such measurements is far from complete. Notably, Welgegund measurement station in South Africa is the only site in continental Africa where e.g. submicron aerosol size distributions are continuously monitored. Welgegund is located in a grazed grassland savanna environment approx. 100 km west of Johannesburg (26.57°S, 26.94°E) at 1480 m above sea level. The station has been operational since May 2010 and is equipped with continuous measurements of aerosol properties such as submicron size distributions, PM10, aerosol particle scattering, absorption-based black carbon (BC) with a MAAP, basic trace gases (SO2, O3, NO, NOx, CO) as well as ecosystem fluxes (CO2, H2O).
Seasonality at Welgegund is characterised with a wet season from October to April, and a dry season from May to September. During the dry season, BC is elevated due to both increased sources (e.g. landscape fires) and reduced wet removal. In the BC time series, a decrease is observed between May 2015 and May 2017. Until May 2015, the mean wet season BC is 0.33 µg m-3, but after May 2017, the mean wet season BC is 0.24 µg m-3. Simultaneously, the mean dry season BC drops from 0.98 µg m-3 to 0.75 µg m-3. For both seasons, the decrease is statistically significant with p-value ≤ 0.001 using Mann-Whitney U test. The decrease in BC affects single scattering albedo at 635 nm, which increases from 0.88 to 0.91 for the wet season and from 0.81 to 0.86 for the dry season, respectively.
Last year, an ACSM for on-line measurement of non-refractory submicron aerosol chemical composition and an on-line GC-MS system for volatile organic compound measurements were added to Welgegund instrumentation. These new measurements, together with the existing long time series, enable more detailed characterisation of aerosol particles and their precursors at the grassland savanna environment at Welgegund.
How to cite: Vakkari, V., Bredenkamp, L., Kulmala, M., Laakso, L., Petäjä, T., and van Zyl, P. G.: 15 years of measurements at Welgegund atmospheric measurement site in South Africa, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19578, https://doi.org/10.5194/egusphere-egu26-19578, 2026.
Aerosol and cloud uncertainty dominates uncertainty in climate prediction (Masson-Delmotte 2021). Aerosol Cloud Interactions (ACIs) are mediated through cloud condensation nuclei (CCN), aerosol particles of large enough size and hygroscopicity to act as seeds upon which cloud droplet can form. Cloud droplet number concentration (CDNC) is determined by both the number of available CCN and the water vapour supersaturation these CCN experience. Variability and uncertainty in CCNC are primarily important in CCN-limited regimes where the CDNC is limited by the number of available CCN. These conditions prevail in much of the boundary layer and lower free troposphere (Rosenfeld et al. 2014). The number concentration of CCN is highly variable, both globally and locally (Schmale et al. 2018), depending on the abundance, size distribution and chemical composition of primary and secondary aerosols from both anthropogenic and biogenic sources. Therefore, CCN and related aerosol observations in different environments are needed to evaluate their representation in global models.
Here we use long-term in-situ observations of CCN number concentrations, particle number size distributions, and particle chemical composition from ground-stations to evaluate CCN representation in the TM5 chemical transport model. We evaluate the default version of TM5 alongside representation of some of the sources of aerosol uncertainty in the model, represented by one-at-a-time sensitivity studies of uncertain aerosol input parameters including emissions of sea salt and biomass burning aerosol, secondary organic aerosol precursors and removal by wet and dry deposition. The model was run for 2017 and 2018, and so ground stations with relevant publicly available observations over at least 9 months of this period are chosen for evaluation including US Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) site at Oklahoma, USA (Southern Great Plains) and ARM mobile facility deployment during the Layered Atlantic Smoke Interactions with Clouds (LASIC) campaign on Ascension Island (Andrews et al. 2025), SMEAR II station in Hyytiälä, Finland (Kulmala 2023) and Kennaook/Cape Grim Baseline Air Pollution Station in Tasmania (Keywood 2018).
References
Andrews, E., Zabala, I., Carrillo-Cardenas, G., et al. 'Harmonized aerosol size distribution, cloud condensation nuclei, chemistry and optical properties at 10 sites', Scientific Data, 12: 937.10.1038/s41597-025-04931-y 2025.
Keywood, M., Ward, J., Derek, N., GAW-WDCA. 'Cloud_condensation_nuclei_number_concentration at Kennaook / Cape Grim Baseline Air Pollution Station, data hosted by EBAS at NILU'.10.48597/Z8RB-RDC9 2018.
Kulmala, M., Petäjä, T. "Particle_number_concentration at Hyytiälä, data hosted by EBAS at NILU." In.https://doi.org/10.48597/RHAH-5H7M 2023.
Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou. "IPCC Climate Change 2021: The Physical Science Basis." In.: Cambridge University Press.10.1017/9781009157896 2021.
Rosenfeld, D., Andreae, M.O., Asmi, A., et al. 'Global observations of aerosol-cloud-precipitation-climate interactions', Reviews of Geophysics, 52: 750-808.https://doi.org/10.1002/2013RG000441 2014.
Schmale, J., Henning, S., Decesari, S., et al. 'Long-term cloud condensation nuclei number concentration, particle number size distribution and chemical composition measurements at regionally representative observatories', Atmos. Chem. Phys., 18: 2853-81.10.5194/acp-18-2853-2018 2018.
How to cite: Williamson, C., Bouchahmoud, M., Zhou, P., Mustonen, L., Bergman, T., Makkonen, R., and Zabala, I.: Evaluating aerosol representation in TM5 chemical transport model using in-situ observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6864, https://doi.org/10.5194/egusphere-egu26-6864, 2026.
Cloud condensation nuclei (CCN) play a central role in regulating cloud microphysical properties and, consequently, aerosol-cloud interactions, which are the largest source of uncertainty of radiative forcing (RF) in global climate models. For an aerosol to be able to act as CCN at certain atmospheric conditions, high enough aerosol hygroscopicity (κ) and particle size (dp) are required. These properties can be directly characterized using cloud condensation nuclei counters (CCNc) and, when measured over extended periods, provide valuable constraints for the representation of aerosol–cloud interactions in climate models. However, long-term CCN observations remain sparse in the Southern Hemisphere, limiting the ability to evaluate and improve model performance using observational constraints.
In this study we focus on measurements from the atmospheric measurement station in Welgegund, South Africa. The station is strategically located to capture air masses influenced by pristine grassland background as well as major anthropogenic source regions. The site is situated approximately 100 km southwest of the Johannesburg–Pretoria conurbation at approximately 1480 m above mean sea level. The coexistence of pristine and polluted air mass influences provides an opportunity to compare the CCN-activity of natural and anthropogenic aerosol in southern Africa, where other measurement stations are sparce.
The aim is to evaluate the potential of using long-term measurements of particle number size distributions (PNSD) produced since 2010 at Welgegund station as a proxy for CCN concentrations. This is done by utilizing an unpublished dataset from a measurement campaign with a CCNc counter during January 2017-April 2017. The analysis will evaluate the commonly used approximation of particles larger than 100 nm as a proxy for CCN during the campaign and then utilize this information to the 15-year PNSD data set. Applicable conditions are first determined by analyzing the characteristics of CCN (κ, critical diameter at given supersaturations dcrit), potential diurnal cycle of CCN concentrations, the correlation to other relevant meteorological parameters and sources of the air masses during the campaign.
In the future, the presented dataset is expected to contribute to the development of a standardized long-term CCN observational framework to support the integration of southern African measurements into global CCN databases. Thereby helping to address the current geographical imbalance of observations, that can be used to reduce climate model RF-uncertainty associated with aerosol–cloud interactions.
How to cite: Mustonen, L., Backman, J., van Zyl, P., Vakkari, V., and Williamson, C.: Exploring the Potential of long-term Aerosol Size Distribution Measurements as Proxies for Cloud Condensation Nuclei in Welgegund, South Africa , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10164, https://doi.org/10.5194/egusphere-egu26-10164, 2026.
Long-term monitoring of PM2.5 mass concentrations and chemical composition provides essential insights into the temporal variation of air pollutants and serves as a basis for evaluating the effectiveness of emission control strategies. Although the Taiwan Ministry of Environment (MOE) has established a nationwide air quality monitoring network comprising over 75 stations, routine measurements of PM2.5 chemical composition are not included. To address this gap, this study collected PM2.5 samples every six days from 2017 to 2023 at six MOE stations—Hualien, Banqiao, Zhongming, Douliu, Chiayi, and Xiaogang—to analyze their chemical composition. The results indicate that sulfate (SO42-), nitrate (NO3-), and organic carbon (OC) were the predominant components, jointly accounting for over 50% of the PM2.5 mass. All three species exhibited decreasing trends across the six sites during the study period. In 2023, compared to 2017, SO42 concentrations decreased by 1.09–2.06 μg m-3 (20–42%), NO3- by 0.27–2.32 μg m-3 (17–36%), and OC by 0.63–1.90 μg m-3 (27–43%). Positive Matrix Factorization (PMF) analysis resolved six major source factors: “Regional pollution,” “Mixed secondary pollution,” “Mixed primary pollution,” “Oil combustion,” “Sea spray,” and “Suspended dust.” The “Regional pollution” and “Oil combustion” sources were strongly associated with transboundary pollution. Notably, the “Oil combustion” factor exhibited a marked decline starting in 2020, coinciding with the implementation of the International Maritime Organization's global sulfur cap (IMO 2020), which limited the sulfur content in marine fuels. Over the seven-year period, the contributions from “Regional pollution” and “Oil combustion” decreased by an average of 29% and 76% across the six stations, respectively. In contrast, “Mixed primary” and “Mixed secondary” pollution were more closely linked to local sources, particularly traffic emissions. The “Mixed primary pollution” factor showed a strong correlation with CO (r = 0.65), with correlation coefficients exceeding 0.7 at the Douliu , Xiaogang, and Zhongming stations, indicating a significant influence from primary traffic emissions. While “Mixed secondary pollution” decreased significantly by 40% on average across the six sites over the last seven years, “Mixed primary pollution” showed only a marginal decline of 5%. In summary, the overall decline in PM2.5 concentrations from 2017 to 2023 can be attributed to reductions in regional pollution and secondary aerosols. However, the stagnation in reducing mixed primary pollution highlights a critical gap, suggesting that future control strategies must prioritize stricter regulations on primary pollutants, encompassing both traffic and industrial emissions.
How to cite: Sun, S. S.-E., Chou, C. C.-K., Lee, C.-T., and Chang, S.-Y.: Long-term reductions in regional pollutants contributed to decreased PM2.5 concentrations in Taiwan from 2017 to 2023, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16637, https://doi.org/10.5194/egusphere-egu26-16637, 2026.
The monitoring of inorganic chlorine species in the stratosphere, particularly hydrogen chloride (HCl), has been a critical measure for the success of the 1987 Montreal Protocol. As the most abundant chlorinated reservoir, HCl levels also reflect stratospheric variability caused by transient events, such as large wildfires. During December 2019 and January 2020, the Australian wildfires injected an unprecedented amount of smoke, containing organic aerosol, into the stratosphere. These particles provided surfaces for heterogeneous chemical reactions, altering the partitioning of chlorine species as a result. To investigate these effects, we used the TOMCAT 3-D chemical transport model to analyse the transport and chemical impact of smoke in the stratosphere in 2020. By incorporating an organic tracer (hexanoic acid) into our simulations, we modelled the evolution of smoke-related aerosol and its observed impact on the HCl distribution and variability.
Output from TOMCAT was evaluated using remote sensing data from the Atmospheric Chemistry Experiment - Fourier Transform Spectrometer (ACE-FTS) solar occultation instrument, along with data from the Aura Microwave Limb Sounder (MLS). ACE-FTS measurements show that HCl concentrations decreased to half their climatological values following the Australian wildfires. Reactivation processes on sulfate and organic aerosol particles contributed to this reduction, accompanied by an increase in active inorganic chlorine species and, in particular, approximately a 4% depletion of southern mid-latitude total column ozone.
Ongoing work explores the potential impact of similar wildfire smoke injections under future conditions, in an atmosphere with less chlorine (and increased methane and nitrous oxide), by performing TOMCAT simulations for the year 2050. These experiments provide insights into inorganic chlorine processing and ozone layer recovery under conditions of increasing wildfire frequency and intensity driven by climate change.
Overall, our findings highlight the role of smoke organic aerosol in perturbing stratospheric chlorine chemistry and ozone. With wildfires expected to become more frequent and severe due to climate change, understanding these processes is essential for attribution of observed trace gas variability and ensuring the underlying recovery of the ozone layer from halogenated ozone-depleting substances.
How to cite: Toso, L., Chipperfield, M., and Harrison, J.: Chlorine Processing by Organic Aerosol from the 2020 Australian Wildfires and Implications for Future Ozone Recovery, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19754, https://doi.org/10.5194/egusphere-egu26-19754, 2026.
