This session welcomes contributions related to the measurement and modeling of radicals, including:
1. Development of novel techniques for detecting radicals, their precursors, and intermediate species;
2. Laboratory studies: determination of gas- and aqueous-phase rate constants, study of complex reaction systems involving halogens, Henry's law and uptake coefficients, UV/VIS spectra, and other properties of reactive species.
3. Adaptation of instruments for various platforms (e.g., ground-based, mobile, shipborne, airborne);
4. Quality assurance and control, such as calibration procedures and intercomparison of different methods;
5. Model development, including new chemical mechanisms, model configurations, and uncertainty analysis;
6. Applications of radical measurements and modeling in field campaigns and satellite-measurements including volcanic plumes as well as chamber studies.
Orals: Fri, 8 May, 14:00–15:45 | Room M2
Bromine monoxide levels in the troposphere are usually very low. Under certain conditions, local concentrations can be enhanced, and if the enhancement is large enough, it can be detected in satellite observations using UV absorption spectroscopy.
Most satellite BrO observations focus on polar regions, where many BrO enhancements occur every spring, resulting in local ozone depletion and impacting atmospheric mercury chemistry. BrO enhancements are also observed in some volcanic plumes, and the BrO-to-SO2 ratio can help better understand magma conditions and possibly even predict changes in volcanic activity. Enhanced tropospheric BrO levels have also been detected in satellite data near salt lakes and salt marshes.
In this study, 8 years of TROPOMI BrO slant columns have been evaluated for stationary BrO signals indicating local sources. In addition to the emissions from Rann al Katch, the Dead Sea, and the Great Salt Lakes, which have already been reported in earlier work, many more local BrO enhancements could be identified, mostly linked to salt lakes and salt marshes. The BrO hotspots are evaluated for potential artefacts from enhanced albedo, surface spectral reflectance, and scene inhomogeneity. For the signals deemed real, the seasonal variation is analysed, and the magnitude of the BrO enhancement is estimated.
How to cite: Richter, A., Zilker, B., and Bösch, H.: A TROPOMI-based survey of stationary BrO sources , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13597, https://doi.org/10.5194/egusphere-egu26-13597, 2026.
Hydroperoxy radicals (HO₂) play a key role in atmospheric oxidative chemistry, participating in the transformation of primary emissions into secondary pollutants such as NO₂ and O₃. The uptake of HO₂ onto atmospheric aerosols can significantly impact ozone production in certain regions,[1] and may partly explain in some environments the overestimation of HO2 concentrations by atmospheric chemistry models compared to field measurements. However, currently there have been limited real time field measurements of the HO2 uptake coefficient (γHO2) for ambient air aerosol particles, conducted in Japan.[2-4]
In this study, a new instrument has been developed to directly measure γHO2 for the first time in the UK. A mixture of O₃ and H₂O vapour in air is introduced into a flow tube, where OH radicals are generated via photolysis of O₃ at 266 nm using a Nd:YAG laser. The OH radicals are then converted to HO₂ using excess CO. The temporal decay of HO₂ is measured by sampling the flow tube into a low pressure cell to sensitively monitor HO2 following its conversion to OH and detection at 308 nm using the laser induced fluorescence technique. To quantify the removal of HO₂ that is due to uptake onto ambient aerosols, the ambient aerosol surface area is first enhanced using a Versatile Aerosol Concentration Enrichment System (VACES).[2] Ambient air is passed through VACES and then into the HO₂ reactivity instrument. Alternating between sampling lines—one containing an aerosol filter and one without—allows separation of gas-phase HO₂ reactivity from the total reactivity. The difference in HO2 reactivity between the measurements with and without the filter is used to quantify the HO₂ uptake onto aerosols, and hence a real time observation of γHO2.
The instrument measured γHO2(ambient aerosols) vs. time at the Manchester Air Quality Supersite, UK in August 2025, alongside supporting measurements of aerosol composition and gas-phase species, including OH, HO2 and RO2 radicals and OH reactivity. This fieldwork enables the correlation of the measured γHO2vs. time with factors such as aerosol composition (e.g. transition metals, inorganic salts and organic species), temperature and humidity. The combined measurements will be used to improve the agreement of HO2 concentrations in atmospheric chemistry models with [HO2] in field measurements and understand the impact of the studied aerosol uptake on O3 production.
[1]. Ivatt et al., Nat. Geosci., 15, 536-540, 2022
[2]. Zhou et al., Atmos. Environ., 223, 117189, 2020
[3]. Zhou et al., Atmos. Chem. Phys., 21, 12243–12260, 2021
[4]. Li et al., Environ. Sci. Technol., 56, 12926−12936, 2022
How to cite: Onel, L., Qin, Z., Whalley, L., Flynn, M., Allan, J., Garner, N., Vallipparambil Babu, A., Boustead, G., and Heard, D.: Real-time field measurements of HO2 uptake coefficients onto ambient aerosols using laser flash photolysis coupled with laser induced fluorescence detection, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10812, https://doi.org/10.5194/egusphere-egu26-10812, 2026.
Tropospheric ozone (O3) is an important air pollutant and short-lived climate forcer that influences climate and poses risks to human health and crop productivity. While reactive halogens are known to destroy ozone, the role of mineral dust as a catalyst for halogen activation remains poorly represented in chemistry–climate models. Here we present a global quantitative assessment of ozone reduction driven by dust-catalyzed chlorine and iodine chemistry.
Using the Community Earth System Model (CESM) with explicit dust-induced halogen activation, we show that mineral dust substantially enhances reactive Cl and I production, particularly in marine outflow regions where dust mixes with sea-salt aerosol. This mechanism leads to a global annual mean reduction of ~5% in surface ozone and ~3% in the tropospheric ozone column. Modeled ozone responses are consistent with satellite observations, reproducing observed 3–6% tropospheric ozone column decreases over the tropical Atlantic during high-dust conditions and improving the spatial agreement of ozone responses to dust relative to simulations without dust-halogen chemistry.
Ozone depletion due to this mechanism is strongest over oceanic dust outflow pathways but propagates inland, affecting continental regions far from dust sources. As a result, dust-driven halogen chemistry reduces growing-season ozone exposure (AOT40) across major agricultural regions, increasing crop productivity by up to 9% in South Asia and by 1–7% across parts of Europe, North America, and West Central Asia. Lower ground-level ozone also reduces ozone-attributable premature mortality, with the largest health benefits occurring in densely populated, dust-influenced regions of Asia.
Our results identify dust-catalyzed halogen activation as a previously underrepresented natural global ozone sink with important implications for air quality, agriculture, human health, and the global oxidizing capacity.
How to cite: Meidan, D., Bossolasco, A., A. Cuevas, C., Villamayor, J., P. Fernandez, R., Li, Q., Fu, X., Sun, X., and Saiz-Lopez, A.: Global Ozone Reduction Driven by Dust-Catalyzed Halogens, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5324, https://doi.org/10.5194/egusphere-egu26-5324, 2026.
ROx radicals (including OH, HO2 and RO2) are central to atmospheric chemistry, governing the removal of trace gases and the formation of secondary pollutants such as ozone and secondary organic aerosols. Despite decades of research since OH radical was recognized as the core atmospheric oxidant, the chemical production and destruction processes of ROx radicals under varied NOx levels remain insufficiently constrained, limiting a mechanistic comprehension of atmospheric oxidation capacity. To address this, the Ensembled eXperiment of Atmospheric oxidation Capacity in the Troposphere (EXACT) campaign was conducted over one year across urban, regional, and background sites in the North China Plain. OH, HO2 and RO2 were measured online using an updated Peking University Laser Induced Fluorescence (PKU-LIF) system during one representative month per season (autumn, winter, spring, summer).
Preliminary results indicate that the daily maximum OH concentrations reached up to 1.5×107 molecules cm-3 in summer, which is five times higher than in winter (~3×106 molecules cm-3). HO2 and RO2 concentrations typically peaked at (2-3)×109 molecules cm-3 in summer across different sites, approximately an order of magnitude higher than (1-2)×108 molecules cm-3 in winter, with spring and autumn exhibiting intermediate levels. Total OH reactivity (kOH) showed distinct spatiotemporal patterns, with daily peak values ranging from 10 s-1 at the background site to over 30 s-1 at the regional site, reflecting the complex mixture of anthropogenic and biogenic VOCs. The seasonal and diurnal variability of ROx concentrations highlights distinct patterns influenced by local environmental conditions and photochemical activity. Based on the comprehensive observational datasets, we perform a detailed experimental budget analysis for individual radicals and their sum (ROx). The research quantifies the contributions of critical radical sources and sinks, and identifies the dominant chemical pathways driving ROx levels under varying NOx conditions. Our findings advance the mechanistic understanding of radical chemistry and provide observational constraints that refine current chemical mechanisms for simulating atmospheric oxidation capacity and secondary pollution formation.
How to cite: Zang, Q., Zhang, C., Ma, X., Tan, Z., Lu, K., Lou, S., and Hu, R.: OH, HO2 and RO2 Radical Chemistry Across North China Plain Informed by Multi-seasonal Observations and Experimental Budgets, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17415, https://doi.org/10.5194/egusphere-egu26-17415, 2026.
The photolysis of nitrous acid (HONO) produces the hydroxyl radical (OH). For decades. HONO measurements have exceeded model predictions, which are often based on gas phase chemistry, and various mechanisms have been proposed as sources of this excess HONO. We report here on airborne remote sensing observations from the mini-DOAS instrument onboard the HALO aircraft during several research missions from various regions (Europe, Asia, the Atlantic) at altitudes up to 15 km. HONO slant column densities detected from limb scattered skylight in the ultraviolet wavelength range using the DOAS technique are converted to volume mixing ratios with the O3/O4 scaling method. These observations form a C-shaped profile in the troposphere which exceed model (EMAC/MECO(n)) predictions by up to an order of magnitude, with volume mixing ratios up to 150 ppt in the boundary layer and more than 100 ppt in the upper troposphere. Together with a plethora of atmospheric parameters and trace gases measured simultaneously onboard HALO, various formation mechanisms are explored to investigate in situ HONO sources. While the photolysis of particulate nitrate can explain HONO in the marine boundary layer over the remote Atlantic, HONO formation in the polluted lower troposphere remains difficult to explain quantitatively. In the cold upper troposphere of the tropics, the aerosol loading was not sufficient to explain the necessary HONO source with heterogeneous chemistry, and a novel gas phase formation mechanism is proposed. The potential formation, lifetime, and oxidation of peroxynitrous acid in the upper troposphere is investigated in some detail.
How to cite: Weyland, B., Rosanka, S., Taraborrelli, D., Bohn, B., Zahn, A., Obersteiner, F., Förster, E., Mertens, M., Jöckel, P., Ziereis, H., Kaiser, K., Fischer, H., Crowley, J. N., Wang, N., Edtbauer, A., Williams, J., Andrés Hernández, M. D., Burrows, J. P., Butz, A., and Pfeilsticker, K.: Potential sources of excess nitrous acid in the troposphere inferred from airborne remote sensing, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14785, https://doi.org/10.5194/egusphere-egu26-14785, 2026.
Mercury is a persistent environmental pollutant with strong impacts in polar regions, where atmospheric oxidation and subsequent deposition drive ecosystem loading and human exposure via methylmercury bioaccumulation. However, atmospheric mercury chemistry remains poorly constrained because gaseous oxidized mercury (Hg(II)) has rarely been resolved at the molecular level under ambient conditions. Most field observations rely on hours-to-days preconcentration techniques that provide limited speciation and are subject to sampling artefacts, leaving key oxidation pathways and deposition estimates largely unvalidated.
Here we present novel in-situ, online molecular measurements of individual oxidized mercury species in remote polar environments. We deployed nitrate-based chemical ionization atmospheric pressure interface time-of-flight mass spectrometry (NO₃⁻ CI-APi-TOF) to detect neutral Hg(II) compounds in real time, complemented by measurements of naturally charged ambient ions (APi-TOF). Observations were conducted in Antarctica at the Aboa station (austral summer 2014–2015) and in the central Arctic during the MOSAiC expedition (spring 2020, >80°N).
In Antarctica, we observe chemically diverse Hg(II) halides, including HgCl₂, HgBr₂, BrHgCl, and iodinated species (ClHgI, BrHgI, HgI₂), with episodic enhancements reaching several hundred pg Hg m⁻³ (reported as Hg mass concentration at STP). In the central Arctic, HgBr₂ is the only Hg(II) halide detected above the limit of detection during April 2020, with concentrations up to ~80 pg Hg m⁻³ and a decline to below detection by June. HgBr₂ maxima coincide with collocated Hg⁰ depletion and ozone variability, consistent with tight coupling to springtime halogen photochemistry.
Thermodynamic calculations support stable clustering of several mercuric halides with NO₃⁻ under inlet conditions, enabling selective detection of pure halides. While the ionization efficiency implies the derived concentrations represent lower limits, the observed magnitudes agree with other polar measurements, indicating that mercuric halides are major contributors to oxidized mercury in the polar boundary layer. The dominance of HgBr₂, and the presence of iodinated Hg(II) species in Antarctica, challenge current chemical transport models that typically predict HgCl₂ and Hg(OH)₂/HOHgBr as dominant oxidized forms. Because individual Hg(II) species differ strongly in photolysis rates, solubilities, and particle uptake, these new speciation constraints imply potentially substantial shifts in predicted mercury lifetime, transport, and deposition.
Our results demonstrate that real-time molecular speciation of oxidized mercury is now feasible in remote environments and provides a critical observational foundation for improving mercury redox chemistry in models and strengthening policy-relevant assessments of polar mercury deposition.
How to cite: Jokinen, T., Gómez Martín, J. C., Feinberg, A., Mahajan, A., Plane, J., Acuña, U., Dávalos, J., Cuevas, C., Quéléver, L., Beck, I., Schmale, J., Junninen, H., Sipilä, M., Kulmala, M., Petäjä, T., and Saiz-Lopez, A.: Direct in-situ molecular speciation of atmospheric oxidized mercury in polar regions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20827, https://doi.org/10.5194/egusphere-egu26-20827, 2026.
Carbonyl oxides, known as Criegee intermediates, are transient species produced in the ozonolysis of unsaturated hydrocarbons. These intermediates play a key role in the chemistry of the troposphere, effecting complex reaction pathways that lead to production of OH radicals, peroxy radicals, highly oxygenated molecules, etc. Currently, Criegee intermediates are studied in isolation from the ozonolysis reaction by synthesis of stabilized carbonyl oxides through the photodissociation of a corresponding iodoalkane and a subsequent addition of O2. This method has permitted the study of various kinetic rate constants and product yields of reactions of Criegee intermediates with compounds of atmospheric interest. However, the ozonolysis reaction is highly exothermic, and the produced Criegee intermediates have a broad energy distribution. Thus, research on Criegee intermediates as a key step of the ozonolysis reaction network, and their effect on the different reaction pathways, requires also the ability of measuring these transient species in the actual ozonolysis reaction.
Here, we report on the direct measurements of formaldehyde oxide produced from ozonolysis of ethene in a flow cell using cavity ring-down spectroscopy. The gas flow and pressure in the optical cavity were carefully controlled to allow the reaction cell to behave as a plug-flow reactor, and high-resolution (0.01nm) ultraviolet spectra were obtained for the ozonolysis of ethene under different reaction conditions. An a priori chemical mechanism was simulated in the plug-flow reactor to determine reaction conditions that would enhance the quasi steady-state production of formaldehyde oxide, which was quantified by fitting the measured ultraviolet spectra with the known cross-section of its B̃(1A′) ← X̃(1A′) transition. Average concentrations of CH2OO were determined in the flow cell under different residence times, and time profiles were obtained corresponding to different steady states. The time profiles serve as constrains to benchmark a posterior reaction mechanism of ethene ozonolysis, allowing for the determination of yields and other kinetic information, as well as providing insights on some yet-unexplored reactions pathways in the ozonolysis reaction network.
How to cite: Campos-Pineda, M., Yang, L., and Zhang, J.: Direct measurements of the Criegee intermediate formaldehyde oxide, CH2OO, produced from ozonolysis of ethene in a plug-flow optical cavity., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14403, https://doi.org/10.5194/egusphere-egu26-14403, 2026.
Chemically reactive atmospheric radicals and their precursors species (such as HO2, NO3, HONO, H2CO, etc.) play a crucial role in the atmospheric chemistry processes. Reliable and real-time assessment of the concentration change of such reactive species in the atmosphere is essential for understanding the oxidation capacity of the atmosphere, which might have a severe impact on air pollution models, prediction of tropospheric chemical processes, regional air quality and global climate change, and political decisions related to emission control strategies. Contrary to long-lived species (such as greenhouse gases), fast, interference-free, accurate, and precise in situ monitoring of such strongly reactive species represents a real challenge due to their very high reactivity resulting in short lifetimes (down to seconds), ultralow concentrations ranging from ppbv (10−9) to ppqv (10−15), and due to the complex reaction networks they participate in.
In this presentation, we will overview our recent progress in the development of spectroscopic measurement technique for optical monitoring of radicals and their precursors, including : (1) novel technique development for lab investigation; (2) intercomparison of different methods in simulation chamber and in real-world field campaign; as well as intercompaison through modeling; (3) applications to field campaigns and chamber studies.
Acknowledgments
This work is partially supported by the French national research agency (ANR) under the Labex CaPPA (ANR-10-LABX-005), ANR MULTIPAS, ANR MABCaM, ANR ICAR-HO2 and PIA SEAM contracts; the PHC-ORCHID project; the EU-INTERREG SAFESIDE project; the EU H2020-ATMOS project (Marie Skłodowska-Curie grant agreement No 872081), and the regional CPER ECRIN, CPER-IRENE, CPER-CLIMIBIO programs.
References
[1] H. Yi, M. Cazaunau, A. Gratien, V. Michoud, E. Pangui, J.-F. Doussin, W. Chen, Intercomparison of IBBCEAS, NitroMAC and FTIR for HONO, NO2 and CH2O measurements during the reaction of NO2 with H2O vapour in the simulation chamber CESAM, Atmos. Meas. Tech. 14 (2021) 5701–5715.
[2] H. Yi, L. Meng, T. Wu, A. Lauraguais, C. Coeur, A. Tomas, H. Fu, X. Gao and W. Chen, Absolute determination of chemical kinetic rate constants by optical tracking the reaction on the second timescale using cavity-enhanced absorption spectroscopy, Phys. Chem. Chem. Phys. 24 (2022) 7396-7404.
[3] W. Chen, H. Yi, T. Wu, W. Zhao, C. Lengignon, G. Wang, E. Fertein, C. Coeur, G. Wysocki, T. Wang, M. W. Sigrist, X. Gao and W. Zhang, Photonic Sensing of Reactive Atmospheric Species, in Encyclopedia of Analytical Chemistry © 2017 John Wiley & Sons, Ltd.
How to cite: Chen, W.: Advance in spectroscopic measurements of key atmosperic radicals and their applications in simulation chamber and field campaign, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14214, https://doi.org/10.5194/egusphere-egu26-14214, 2026.
Tropospheric ozone (O3), the third most important greenhouse gas, has harmful effects on human health, vegetation and climate. Indeed, increases in O3 are associated with a higher risk of respiratory illnesses, and significant impacts on crop yields have been reported.The formation chemistry of tropospheric ozone is complex and nonlinear, involving photochemical reactions driven by nitrogen oxides (NOx = NO + NO2) and volatile organic compounds (VOCs). Locally, the O3 budget is governed by advection, net local production, and dry deposition. To identify the major production pathways contributing to the net local production rate, P(O3), and distinguish it from advected O3 pollution, a technology capable of monitoring P(O3) has been developed. This instrument is referred to in the literature as Measurement of Ozone Production Sensor (MOPS) or Ozone Production Rate instrument (OPR).
Before field deployment, the performance of this type of instruments must be tested to ensure its reliability and accuracy. In this study, we present an evaluation methodology developed to assess the performance of an OPR instrument. We demonstrate how a small gas-generation unit, capable of providing synthetic air mixtures of VOCs and NOx to the OPR, can be combined with a lamp-based irradiation system covering the OPR to evaluate its performance. In this approach, the ozone production rate P(O3) within the OPR is simulated using the Framework for 0-D Atmospheric Modeling (F0AM), an open-source MATLAB-based box model. We present laboratory tests of the IMT OPR instrument under various controlled conditions spanning ozone production regimes from NOx-limited to NOx-saturated. The reliability and limitations of this combined experimental–modeling approach and the performance of the IMT OPR instrument are discussed.
Acknowledgments. This work was performed as part of the OSEAMS project, funded by the French national agency (ANR) and the National Science and Technology Council (NSTC).
How to cite: Ferrand, B., Jamar, M., Tomas, A., and Dusanter, S.: A New Methodology for Evaluating Ozone Production Rate Instruments , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9337, https://doi.org/10.5194/egusphere-egu26-9337, 2026.
Changes of O3 and OH are important because they are the major atmospheric oxidants. Both O3 and OH concentrations in Pearl River Delta in southern China have been increasing significantly since 2006, raising serious environmental concerns. In this study, Observation Based Methods (OBM) are developed for OH and Photochemical O3 Production Index (PPI) to investigate the inter-annual variability and trends of OH and O3. We found that the overall trends of PPI, OH and O3 in 2006-2021 could mostly be attributed to the reduction in NO2 concentrations due to emission control of NOx. However, the short-term (less than 5 years) inter-annual variations of PPI, O3 and OH were primarily driven by meteorological processes.
How to cite: Liu, S. C.: Changes of O3 and OH in Pearl River Delta, China in 2006-2021, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6616, https://doi.org/10.5194/egusphere-egu26-6616, 2026.
Posters on site: Fri, 8 May, 10:45–12:30 | Hall X5
Roughly 90 % of the oxidation of the key greenhouse gas (GHG) methane (CH4) is driven by reaction with the hydroxyl radical (OH) with ~50 % of this processing occurring over the oceans. Ocean emissions of volatile organic compounds (VOCs) have the potential to modify the oxidation capacity (by acting as a sink for OH) and influence the lifetime of CH4. The oxidation of ocean-emitted VOCs may also lead to the formation of secondary organic aerosols (SOA) and ozone (another GHG) and further influence the climate.
Combined observations of OH, peroxy radicals and OH reactivity within the remote marine boundary layer are sparse. Ground-based observations can provide insights into factors influencing the oxidation capacity in this type of environment, but do not allow any spatial variability in ocean emissions to be determined.
Here, ship-borne observations of OH, HO2, RO2 and OH reactivity made in the North Atlantic Ocean on board the RSS Discovery in June 2025 are presented. The observed OH, HO2 and RO2 will be compared to a preliminary radical budget analysis to assess the major radical sources and sinks. The OH reactivity observed in the North Atlantic as the ship travelled through waters with a range of marine biological activity will be compared to OH reactivity calculated from the coordinated observations of CO, CH4, O3, NOx and VOCs (including oxygenated VOCs measured using PTR-MS and alkanes, alkenes and aromatics measured using canister samples and subsequent GC analysis) to assess the variability in oceanic emissions, the variability in any missing OH reactivity and the impact this missing OH reactivity has on our understanding of the oxidation capacity.
How to cite: Whalley, L., Mostapha, S., Stone, D., Heard, D., Yang, M.-X., Monreal-Campos, I., An, H., Hopkins, J., Stapleton, C., Drysdale, W., Job, J., Lee, J., Petherick, P., and Edwards, P.: Ship-borne observations of OH, HO2, RO2 and OH reactivity in the North Atlantic Ocean, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6732, https://doi.org/10.5194/egusphere-egu26-6732, 2026.
The hydroxyl (OH) radical serves as the core driver of atmospheric oxidation processes. However, its low concentration and high reactivity pose substantial challenges to accurate measurement in complex atmospheric environments. This study explores a high-sensitivity Laser-Induced Fluorescence (LIF) detection approach based on chemical modulation. An efficient Chemical Titration Cell (CTC) was developed, and key parameters including OH scavenger concentration and flow rate were systematically optimized, resulting in an OH removal efficiency of over 99% and a transmission efficiency of 89%. A high-sensitivity detection system for atmospheric OH radicals based on chemical modulation (CM-LIF) is proposed herein. By optimizing the fluorescence cell, Sampling structure, and minimizing background laser scattering, the system’s measurement accuracy and detection sensitivity are improved. The detection limit reaches (1.78 ± 0.17) × 105 cm-3 with an integration time of 30 s. A comprehensive set of field observation experiaments and comparative analyses were carried out. Measurement results obtained via chemical modulation and laser wavelength modulation analyses show excellent consistency (slope = 0.95, R2 = 0.89). Moreover, in environments with high ozone levels and elevated alkene concentrations, no unknown interferences were detected other than the well-quantified ozone laser photolysis interference. This study demonstrates that the CM-LIF technique offers a reliable solution for the precise measurement of OH radicals in complex atmospheres. This achievement holds significant scientific value, as it enables quantitative assessment of atmospheric oxidation capacity and facilitates the investigation of secondary pollution transformation mechanisms.
How to cite: Hu, R., Cai, H., Lin, C., Zhang, G., and Xie, P.: Enhanced laser-induced fluorescence instrument based on chemical modulation for OH radical measurement: High-sensitivity detection and interference evaluation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9153, https://doi.org/10.5194/egusphere-egu26-9153, 2026.
As a key reactive iodine species, iodine monoxide (IO) plays a significant role in atmospheric oxidative capacity and particle formation. We developed a newly designed dual-optical cell Differential Optical Absorption Spectroscopy (DOAS) system to generate and measure IO radical. IO was produced through the photochemical interaction between molecular iodine (I₂) and ozone (O₃), allowing independent control of precursor and oxidant levels. By varying I2 or O₃ concentrations under stable environmental conditions, we demonstrate that IO can be generated reproducibly and maintained at steady concentrations over experimental timescales. The measured IO concentrations were subsequently used to constrain a zero-dimensional box model incorporating state-of-the-art iodine chemistry. Model development focused on revising key reaction pathways governing I₂-O₃ interactions and subsequent IO formation, motivated by discrepancies between observed and simulated IO at high oxidant levels. Adjustments to branching ratios significantly improved model performance, with correlation coefficients (R) between observed and simulated values exceeding 0.9 and slope error below 23%. The dual-optical cell DOAS system is suitable to provide a stable and reproducible IO source for instrument calibration and chemical mechanism evaluation.
How to cite: Wang, S., Yan, Y., Jiang, Z., and Zhou, B.: A newly designed dual-optical cell DOAS system for generating and measuring iodine monoxide radical and observation-constrained model development, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-23025, https://doi.org/10.5194/egusphere-egu26-23025, 2026.
Atmospheric chlorine radical plays essential roles in tropospheric photochemical processes, such as affecting the oxidation capacity and aerosol formation. Tropospheric chlorine chemistry was initially known to be important in the marine and polar atmosphere; nevertheless, more and more recent studies have indicated that chlorine chemistry was also active in polluted areas including the urban and marine-coastal environment. Here, we will present the vital chlorine radical precursors, such as nitryl chloride (ClNO2), molecular chlorine (Cl2) and hypochlorous acid (HOCl) that were observed recently in a typical polluted urban (Shijiazhuang) and a marine-coastal (Zhuhai) atmosphere of China. We measured significant concentrations of ClNO2, Cl2, and HOCl at the polluted urban and marine-coastal sites, showing there is active chlorine chemistry at both environments. We will discuss the formation mechanism of these species, as well as the possible of influence from anthropogenic chlorine sources. We will finally discuss their contribution the radical formation and impacts on the atmospheric oxidation capacity at both environments.
How to cite: Tham, Y. J., Zhu, X., and Tao, W.: Chlorine chemistry and its impacts in the polluted urban and marine-coastal atmosphere, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17095, https://doi.org/10.5194/egusphere-egu26-17095, 2026.
Atmospheric radicals critically govern tropospheric oxidation processes, yet chemical models systematically underestimate OH and HO2 under high- and low-NOₓ conditions, limiting accurate prediction of haze and ozone in polluted regions like China. To address these gaps, the Ensembled eXperiment of Atmospheric oxidation Capacity in the Troposphere (EXACT) was conducted across the North China Plain, deploying advanced instrumentation at urban (Beijing), rural (Luancheng), and remote (Shangdianzi) sites over four seasons from autumn 2024 to summer 2025.
Preliminary results reveal strong seasonal variability: peak OH concentrations reached ~2×107 cm-3 in spring and summer but dropped to ~2×106 cm-3 in winter. Significant nighttime HO2 and RO2 were observed in rural and remote areas, indicating active dark chemistry. OH-j(O1D) correlations strengthened from winter (R2≈0.5) to summer (R2≈0.8), reflecting increasing photochemical dominance. HONO photolysis dominated ROx production in winter, while O3 and carbonyl photolysis became more important in warmer seasons. Chlorine chemistry also contributed significantly to ROₓ, with distinct diurnal ClNO2 patterns suggesting multiple source mechanisms.
Compared to earlier campaigns, EXACT shows elevated OH turnover rates since 2020, offering a partial explanation for slowed PM2.5 decline and rising ozone. Building on these findings, the EXACT-Plus campaign will expand into central China’s Gan-E-Xiang region, where complex terrain, high humidity, and unique chlorine sources, such as kilns, fireworks, and biomass burning, may drive unexplored oxidation pathways. This work advances understanding of radical-driven pollution and supports improved model development and air quality management.
How to cite: Tan, Z., Ma, X., Lu, K., Hu, R., and Lou, S.: Overview of the EXACT Campaign and Establishing an Oxidation Network in China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16530, https://doi.org/10.5194/egusphere-egu26-16530, 2026.
The monitoring of greenhouse gas (GHG) emissions is essential to reliably assess key drivers of climate change. Accurate GHG inventories provide the quantitative basis for mitigation and adaption strategies under global warming. The ITMS project (“Integriertes Treibhausgas Monitoringsystem”, in English “integrated GHG monitoring system”)[1], is designed to establish an operational GHG data assimilation service at the German Meteorological Service (DWD) based on the model system ICON-ART[2] to enable Germany to operationally monitor the sources and sinks of three important GHGs: carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O).
In the first phase of the ITMS project DWD together with the Karlsruhe Institute of Technology (KIT) and other partners are focusing on the emission, distribution and depletion of methane. In the troposphere, methane is mainly depleted by the chemical reaction with the OH radical. Tropospheric OH is created mostly by photodissociation of ozone (O3) and thus its abundance depends mainly on the available solar UV radiation and the ozone concentration. The calculation of this chemical system is computationally expensive. Therefore, a simplified calculation of the OH chemistry has to be included in the ICON-ART forward model.
Here, we present a super-simplified OH chemistry scheme for ICON-ART, a data-driven approach based on Minschwaner et al., 2011[3]. The OH concentration is hereby estimated based on the solar zenith angle (SZA) at the respective grid cell. The required parameters are pre-trained on SZA information and OH concentration. We test two independent training datasets – the CAMS global reanalysis (EAC4)[4] and an in‑house chemistry‑climate simulation using the EMAC (ECHAM/MESSy Atmospheric Chemistry) model[5] – and find that the scheme yields reasonable results for both.
[1] www.itms-germany.de
[2] Schröter, J., Rieger, D., Stassen, C., Vogel, H., Weimer, M., Werchner, S., Förstner, J., Prill, F., Reinert, D., Zängl, G., Giorgetta, M., Ruhnke, R., Vogel, B., and Braesicke, P.: ICON-ART 2.1: a flexible tracer framework and its application for composition studies in numerical weather forecasting and climate simulations, Geosci. Model Dev., 11, 4043–4068, https://doi.org/10.5194/gmd-11-4043-2018, 2018.
[3] Minschwaner, K., Manney, G. L., Wang, S. H., and Harwood, R. S.: Hydroxyl in the stratosphere and mesosphere – Part 1: Diurnal variability, Atmos. Chem. Phys., 11, 955–962, https://doi.org/10.5194/acp-11-955-2011, 2011.
[4] Inness, A., Ades, M., Agustí-Panareda, A., Barré, J., Benedictow, A., Blechschmidt, A.-M., Dominguez, J. J., Engelen, R., Eskes, H., Flemming, J., Huijnen, V., Jones, L., Kipling, Z., Massart, S., Parrington, M., Peuch, V.-H., Razinger, M., Remy, S., Schulz, M., and Suttie, M.: The CAMS reanalysis of atmospheric composition, Atmos. Chem. Phys., 19, 3515–3556, https://doi.org/10.5194/acp-19-3515-2019, 2019.
[5] Jöckel, P., Kerkweg, A., Pozzer, A., Sander, R., Tost, H., Riede, H., Baumgaertner, A., Gromov, S., Kern, B., Development cycle 2 of the Modular Earth Submodel System (MESSy2), Geoscientific Model Development, 3, 717-752, https://doi.org/10.5194/gmd-3-717-2010, 2010.
How to cite: Dietz, P., Ruhnke, R., Kirner, O., and Braesicke, P.: A super-simplified OH chemistry scheme for ICON-ART, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12995, https://doi.org/10.5194/egusphere-egu26-12995, 2026.
The hydroxyl radical, OH, is the major daytime oxidant in the troposphere, it controls the lifetime of methane and reacts with volatile organic compounds (VOCs), emitted from both anthropogenic and biogenic sources, often forming formaldehyde as a product. OH is technically difficult to measure, owing to its low atmospheric concentrations, but Wolfe et al., demonstrated that the variation in HCHO concentration can reflect the variation in OH, methane and VOC concentrations and using this relationship were able to estimate OH concentrations during ATom flights [1].
Taking measurements of HCHO made during the PEROXY campaign at the Cabo Verde observatory in 2023, this work presents, the effective yield of HCHO from all OH reactions (α) calculated by determining α from each VOC measured during the campaign and also using a detailed box model run with the Master Chemical Mechanism [2] and constrained to the observed VOCs to account for HCHO formed from OH reactions with the model generated intermediate species. The daytime average α calculated from the model was ~ 0.126, whilst α calculated from the individual VOCs was ~0.08 demonstrating that the reaction of OH with model-generated intermediates species like PAN can act as a small source of HCHO and should be taken into account.
Using the α determined by the model, the concentration of OH was calculated and compared to the OH measured during the campaign using 1) the model-predicted kOH and modelled HCHO and 2) the measured kOH and measured HCHO from the campaign. OH calculated using measured kOH and HCHO was found to be greater than the OH calculated using the modelled predicted values and greater than the observed OH. This suggests that missing kOH is likely an unmeasured VOC which acts as a source of HCHO and, as such, α is likely greater than calculated by the model. This finding highlight that the unknown VOCs (if not considered) could lead to OH concentrations being over-estimated using the approach outlined.
[1] Wolfe G. M. et al., Mapping hydroxyl variability throughout the global remote troposphere via synthesis of airborne and satellite formaldehyde observations, PNAS, 2019, 116, 11171-11180.
[2] Master Chemical Mechanism, MCMv3.3.1, http://mcm.york.ac.uk/MCM/, (accessed April 2025).
How to cite: Babu, A., Seldon, S., Boustead, G., Lade, R., Read, K., Callaghan, A., Punjabi, S., Lee, J., Carpenter, L., Neves, L., Heard, D., and Whalley, L.: A Detailed Study Calculating Hydroxyl Radical Concentration from Formaldehyde and VOC Measurements Made During the PEROXY Campaign, Cape Verde,2023, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6339, https://doi.org/10.5194/egusphere-egu26-6339, 2026.
The ozone layer acts as Earth’s primary shield against harmful ultraviolet radiation. Since the mid-20th century, anthropogenic emissions of long-lived chlorinated compounds have disrupted the photochemical balance controlling stratospheric ozone abundance, leading to severe depletion most evident with the formation of the Antarctic ozone hole. While the dominant role of anthropogenic chlorine in global stratospheric ozone depletion is well established, the influence of naturally emitted short-lived halogens, particularly bromine and iodine, on the timing, magnitude and regional variability of ozone loss has been so far overlooked. Using comparative chemistry-climate modeling experiments that include and exclude natural halogen sources for the 1910-2100 period, we show that natural halogen chemistry accounts for up to half of the total halogen-induced ozone loss in the lower extrapolar (60º S – 60º N) stratosphere during recent decades (1990-2020). This contribution is projected to rise sharply, exceeding 80% by the end of the century (2080-2099). Natural halogens also amplify lower-stratospheric ozone loss along the Antarctic periphery by about 35% in recent decades, most notably delaying the projected recovery of its natural seasonal ozone cycle by nearly five decades. Our results demonstrate the disproportionate per-unit-of-mass efficiency of natural bromine and iodine relative to anthropogenic chlorine in controlling lower stratospheric ozone loss. These findings underscore the key but previously overlooked role of natural halogens in the past-to-future spatiotemporal evolution of global stratospheric ozone balance and highlight the need to accurately represent natural halogen chemistry in past and future projections of the stratospheric ozone layer.
How to cite: Villamayor, J., Fernandez, R. P., Meidan, D., Reynoso, A., Cuevas, C. C., Kinnison, D. E., and Saiz-Lopez, A.: Natural Halogens Modulate the Evolution of Global Stratospheric Ozone Depletion , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6849, https://doi.org/10.5194/egusphere-egu26-6849, 2026.
Halogen chemistry is a central element of tropospheric ozone depletion events (ODEs) during polar spring. Key processes such as sources of reactive halogen species, their transport, and interhalogen interactions as well as the influence of anthropogenic pollution and climate change, however, remain in the focus of Arctic research.
We deployed a long-path DOAS (Differential Optical Absorption Spectroscopy) instrument in Utqiagvik (formerly Barrow), Alaska, in December 2023, and observed enhanced bromine monoxide (BrO) coinciding with reduced ozone concentrations between March and May in 2024 and 2025. By linking these ground-based measurements with satellite observations from TROPOMI and GOME-2B, we aim to improve our understanding of local, regional, and large-scale processes. The results of this comparison highlight the importance of considering the different measurement geometries to capture both near-surface and elevated BrO layers. The findings further suggest that the long-path DOAS measurements are particularly sensitive to bromine activation at an early stage. Therefore, continued ground-based observations are necessary to better characterise near-surface BrO abundances, complementing advances in global satellite monitoring.
How to cite: Lauster, B., Donner, S., Frieß, U., Platt, U., Reischmann, L., Richter, A., Simpson, W., Ziegler, S., Zilker, B., and Wagner, T.: Bridging the Gap: Combining Long-Path DOAS and Satellite Observations to Understand Arctic Bromine Chemistry, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9133, https://doi.org/10.5194/egusphere-egu26-9133, 2026.
In this work, we examine the ozonolysis of selected HFOs and HCFOs in the 123 L EXTreme RAnge (EXTRA) chamber, a Teflon®-coated stainless-steel reactor,⁵ under atmospheric conditions (25 °C, 1 atm). Studies of four HFOs demonstrate that ozonolysis can produce either the GHG HFC-23 or carbon tetrafluoride (PFC-14). HFC-23 is formed from HFO-1234ze(E) in a yield of
Figure 1. Experimentally determined ozonolysis product yields at 298 K and 1 atm pressure of: Left panel: HFC-23 from HFO-1234ze(E); Middle panel: PFC-14 from HFO-1225ye(E), HFO-1225ye(Z), and HFO-1234yf; Right panel: CFC-13 from HFCO-1233xf. Different symbols distinguish separate experiments. The panels show the ratio of products to initial HFO or HCFO concentrations plotted against the fractional change in the HFO or HCFO concentration.
1 B. Burkholder, R. A. Cox, A. R. Ravishankara, Chem. Rev., 2015, 115, 3704.
2 J. Wallington, M. P. Sulbæk Andersen, O. J. Nielsen, Chemosphere, 2015, 129, 135.
3 R. McGillen, Z. T. P. Fried, M. A. H. Khan, K. T. Kuwata, C. M. Martin, S. O’Doherty, F. Pecere, D. E. Shallcross, K. M. Stanley, K. Zhang, Proc. Natl. Acad. Sci. USA, 2023, 120, e23127141204.
4 J. Nielsen, M. P. Sulbaek Andersen, T. J. Wallington, Atmos. Environ., 2025, 343, 120953.
5 E. Leather, M. R. McGillen, C. J. Percival, Phys. Chem. Chem. Phys.,2010, 12, 2935.
6 M.d.l.A. Garavagno, A. Wenger, R. E. T. Holland, B. R. Fena, S. D. Goldstein, D. E. Hicks, F. Liu, J. B. Madell, S. J. Solomon, K. T. Kuwata, M. R. McGillen, M. A. H. Khan, D. E. Shallcross, K. M. Stanley, A. J. Orr-Ewing, Environ. Sci. Technol., 2025, 59, 26031.
How to cite: Garavagno, M. D. L. A., Stanley, K., Shallcross, D., and Orr-Ewing, A.: Tropospheric degradation of Fourth-Generation halocarbons by O3: Formation of long-lived greenhouse gases and ozone-depleting substances, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11358, https://doi.org/10.5194/egusphere-egu26-11358, 2026.
Volcanoes are a natural source of halogens for the atmosphere. After water, carbon dioxide and sulphur compounds, halogens are often the most common gases in volcanic plumes. Over the past two decades, progress has been made in the study of volcanic emissions, particularly those of the heavy halogens bromine and iodine. This contribution provides an interdisciplinary literature review on the current state of the art, and including also some unpublished data, in particularly with regard to bromine and iodine emissions. A detailed global emission estimate is provided, including an analysis of global distribution and comparison with different natural sources. Although volcanoes are point sources with sometimes very high halogen concentrations (mixing ratios in the ppb range), after all their global source strength is rather low compared to other natural halogen sources such as the ocean. The contribution of volcanoes to global halogen emissions into the atmosphere is only in the low percentage range, with the possible exception of extremely large eruptions. However, the spatial distribution of the emissions is quite inhomegeous, so that halogen emissions from volcanoes can still have a local and regional impact on the atmosphere that has not yet been sufficiently investigated.
How to cite: Bobrowski, N.: Reviewing volcanic halogen emissions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12396, https://doi.org/10.5194/egusphere-egu26-12396, 2026.
The hydroxyl radical (OH) is the primary oxidizing agent in the atmosphere, making characterization of its variability essential for accurate forecasting and reanalysis of greenhouse gases and air pollutants such as methane. We seek to understand and quantify the processes governing OH anomalies, with a focus on the El Niño–Southern Oscillation (ENSO). In this presentation, we share results from the Tropospheric Chemical Reanalysis (TCR) data assimilation system, analyzed using a machine learning approach. Our results indicate that the spatio-temporal variability of monthly mean OH anomalies in the tropics from 2019-2024 can, to a large extent, be attributed to variations in nitrogen dioxide (38%), ozone (20%), carbon monoxide (15%), and specific humidity (21%). We find that anomalies in these species are linked to ENSO in both space and time. The spatial pattern of OH variability in the Tropics also shows the imprint of ENSO through these gases. When considering the time-mean OH anomaly, three variables are sufficient to explain the majority of the variance, namely nitrogen dioxide (46%), carbon monoxide (30%), and ozone (15%). These findings imply that questions regarding the contribution of the OH sink to the observed global growth rate of atmospheric methane may be addressed using only these three historically well-observed variables. Furthermore, our method delivers important new Information about regional variations in OH, required for a reliable process attribution in inverse modeling studies.
How to cite: Rijsdijk, P., Miyazaki, K., Sekiya, T., Eskes, H., and Houweling, S.: Attribution of tropical hydroxyl radical variability from amulti-species chemical data assimilation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18483, https://doi.org/10.5194/egusphere-egu26-18483, 2026.
Dinitrogen pentoxide (N₂O₅) plays a central role in nighttime nitrogen oxide chemistry, acting as both a temporary NOx reservoir and an efficient pathway for permanent NOₓ removal through heterogeneous uptake on to aerosols. The nitrate radical (NO₃) serves as a key intermediate linking ozone and nitrogen dioxide to N₂O₅ formation and exists only under nighttime conditions, making it a critical component of nocturnal oxidation chemistry. In this study, we examine nighttime NO3 and N₂O₅ behavior at two urban sites in Taiwan with contrasting fog frequencies, using surface observations of trace gases and meteorology together with satellite-based identification of fog and low cloud conditions. A box modeling framework was employed to estimate the nighttime evolution of NO₃ and N₂O₅ concentrations across a range of fog-likely and fog-free conditions. By comparing the nocturnal N2O5 chemistry across these conditions, we assess how the presence of liquid water modifies the partitioning of reactive nitrogen and the efficiency of nocturnal NOₓ loss. The analysis focuses on differences in inferred N₂O₅ abundance and persistence, with particular attention to conditions favorable for enhanced nitrate production. Model results indicate that efficient N₂O₅ loss to fog droplets shifts the NO₃ / NO₂ / N2O5 equilibrium, reinforcing N₂O₅ formation and accelerating reactive nitrogen removal from the gas phase. These findings underscore the importance of fog in regulating nighttime NOₓ chemistry and highlight N₂O₅ as a major pathway linking urban emissions to secondary aerosol nitrate formation.
How to cite: Griffith, S. M., Wang, J.-L., and Lin, N.-H.: Nighttime N₂O₅ Chemistry in Fog-Influenced Urban Environments: Implications for NOₓ Removal and Aerosol Nitrate Formation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18091, https://doi.org/10.5194/egusphere-egu26-18091, 2026.
An upgraded Peking University Laser-Induced Fluorescence (PKU-LIF) system for synchronized measurements of atmospheric OH, HO₂, and RO₂ radicals will be presented. The system features five integrated modules: (1) A Laser Source based on a frequency-doubled dye laser delivering 308 nm radiation at 8 kHz, with 90% power allocated to ambient measurements and 10% to reference monitoring; (2) An Ambient Radical Measurement Module comprising two detection cells, OH-HOx and HOx-ROx, where OH-HOx is used for the measurement of OH and HO2, and HOx-ROx cell combined with a convertor is used for the efficient conversion and detection of RO2. (3) A Calibration Module employing 185 nm Hg lamp photolysis to generate equal OH/HO₂ concentrations, with CO or CH₄ addition enabling quantitative conversion to HO₂ or CH₃O₂ for sensitivity determination; (4) A Chemical Modulation Module featuring a specially designed Teflon cylinder that ensures vertical airflow alignment and provides 96% OH scavenging efficiency through propane/N₂ injection; (5) A Reference Module with real-time wavelength stabilization using thermocatalytically generated OH, demonstrating exceptional long-term stability (0.2%/hour drift). Recently, the upgraded PKU-LIF system has been applied to the EXACT (Ensembled eXperiments of Atmospheric oxidation Capacity in the Troposphere) campaign to investigate the seasonal evolution of atmospheric radical chemistry and atmospheric oxidation capacity.
How to cite: Zhang, C., Chen, S., Zang, Q., Wang, Y., Ma, X., Tan, Z., Lu, K., and Zhang, Y.: An Updated PKU-LIF System for Synchronized Measurements of OH, HO2 and RO2, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10405, https://doi.org/10.5194/egusphere-egu26-10405, 2026.
Methyl bromide (CH₃Br) and sulfuryl fluoride (SO₂F₂) are widely used fumigants in agriculture and quarantine and pre-shipment activities, leading to atmospheric emissions. While methyl bromide is both anthropogenic and naturally emitted, its regulation under the Montreal Protocol has driven a strong decline in use due to its ozone-depleting potential (ODP = 0.57) and short atmospheric lifetime (~0.8 years). In contrast, SO₂F₂ has increasingly been adopted as a replacement for CH₃Br and is a potent greenhouse gas, with a 100-year global warming potential of 4090.
We present an observation-based analysis of European emissions of CH₃Br and SO₂F₂ covering the period 2003–2023. Emissions are quantified using long-term atmospheric measurements from four European stations combined with an atmospheric transport model and an inversion framework. Our results show a marked decline in CH₃Br emissions consistent with regulatory controls, alongside a rise in SO₂F₂ emissions until around 2020.
This study provides the first long-term, top-down assessment of European SO₂F₂ emissions and evaluates regulatory compliance for CH₃Br. The findings highlight the importance of sustained atmospheric monitoring to track substitution effects and assess the climate implications of ozone-safe but high-GWP alternatives.
How to cite: Graziosi, F., Manning, A., Western, L., and Maione, M.: Replacing Methyl Bromide with Sulfuryl Fluoride: Long-Term Trends in European Fumigant Emissions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11318, https://doi.org/10.5194/egusphere-egu26-11318, 2026.
Tropospheric ozone (O₃) is a key greenhouse gas that adversely affects human health, ecosystems, and climate; the economic cost associated with ozone pollution worldwide is already substantial and tropospheric ozone concentrations are projected to increase under future climate change scenarios, particularly in Southeast Asia. Ambient O3 concentrations are driven by various physicochemical processes including air mass transport, net chemical in-situ production, P(O3), and dry deposition, but the chemistry driving P(O3) is highly complex and characterized by a nonlinear set of photochemical reactions involving nitrogen oxides (NOx = NO + NO2) and volatile organic compounds (VOCs). The inherit uncertainty of estimating P(O3) limits our understanding of the tropospheric ozone budget, i.e. distinguishing between locally-produced ozone and transported pollution, while measuring P(O3) in-situ would provide an important constraint on the ozone budget.
As part of the bilateral France-Taiwan OSEAMS (tropospheric Ozone in Southeast Asia: budget and Mitigation Strategies) project, a five-week field campaign was conducted in a highly polluted urban-industrial area of Kaohsiung, Taiwan. An Ozone Production Rate (OPR) instrument that measures P(Ox) [Ox=O3+NO2], as well as complementary instruments such as a Proton Transfer Reaction-Mass Spectrometer, were deployed next to existing Taiwan-EPA and PAMS (Photochemical Assessment Monitoring Stations) stations. In this study, we present preliminary results including measurements of VOCs, NOx and ozone production rates. We discuss the diurnal variability of these measurements and provide first insights into the contribution of in-situ O3 production to ambient O3 levels, as well as the main chemical pathways of ozone formation affecting an industrial-urban area in southern Taiwan.
Acknowledgments. This work was performed as part of the OSEAMS project, funded by the French National Research Agency (ANR) and the National Science and Technology Council (NSTC) in Taiwan.
How to cite: Dusanter, S., Ferrand, B., Lee, Y.-H., Jamar, M., Wang, J.-L., Lin, N.-H., Griffith, S., and Tomas, A.: Experimental investigation of the ozone budget in Taiwan during the OSEAMS campaign, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16634, https://doi.org/10.5194/egusphere-egu26-16634, 2026.
