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Halogens in the Troposphere

Reactive halogen species can have an important influence on the chemistry of the troposphere. For instance, chlorine atoms react faster with most hydrocarbons than OH does and inorganic bromine and iodine can catalytically destroy tropospheric ozone and oxidise mercury. These reactions have been shown to be important in in environments as different as the polar troposphere during the springtime ozone depletion events, the boundary layer over salt lakes, and volcanic plumes. There is strong evidence that halogens play a spatially even wider role in the marine boundary layer and free troposphere for ozone destruction, changes in the ratios of OH/HO2 and NO/NO2, destruction of methane, in the oxidation of mercury and in the formation of secondary aerosol. There are indications that both, oceanic sources as well as the chemistry of halogens and volatile organic compounds (VOCs) and oxygenated VOCs (OVOCs) in the tropics are linked with potential implications not only for the photochemistry but also the formation of secondary organic aerosol (SOA). More recently, marine emissions of active halogens have been linked to potential impacts on oxidants loading in coastal cities. Finally, bromine and iodine are also being proposed as proxies of past sea ice variability.

We invite contributions in the following areas dealing with tropospheric halogens on local, regional, and global scales:

- Model studies: Investigations of the chemical mechanisms leading to release, transformation and removal of reactive halogen species in the troposphere. Studies of consequences of the presence of reactive halogen species in the troposphere.

- 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 halogen species.

- Field experiments and satellite studies: Measurements of inorganic (X, XO, HOX, XONO2, ..., X = Cl, Br, I) and organic (CH3Br, CHBr3, CH3I, RX, ...) reactive halogen species and their fluxes in the troposphere with in situ and remote sensing techniques.

- Measurements and model studies of the abundance of (reactive) halogen species in volcanic plumes and transformation processes and mechanisms.

- All aspects of tropical tropospheric halogens and links to (O)VOCs: their chemistry, sources and sinks, and their impact on local, regional, and global scales.

Convener: Alfonso Saiz-Lopez | Co-conveners: Nicole Bobrowski, Rolf Sander, Ulrich Platt
| Mon, 23 May, 08:30–09:54 (CEST)
Room 0.31/32

Mon, 23 May, 08:30–10:00

Chairpersons: Nicole Bobrowski, Ulrich Platt

Juan Carlos Gomez Martin et al.

Iodine chemistry is a driver of new particle formation in the marine and polar boundary layer, with potential influence on cloud formation and properties. There are however conflicting views about how iodine gas-to-particle conversion proceeds. Laboratory studies indicate that iodine photooxidation yields iodine oxides, which are well-known particle precursors1. By contrast, nitrate ion chemical ionization mass spectrometry (CIMS) field and environmental chamber observations have been interpreted as evidence of nucleation of iodine oxoacids2,3. Here, we report flow tube laboratory experiments showing that iodine oxides react with nitrate core ions to generate the same ions observed by CIMS instruments. Therefore, we conclude that molecules unlikely to form in the atmosphere in the gas-phase such as iodic acid are not necessary to explain CIMS field measurements, but rather obscure their meaning, whereas iodine oxides explain the field observations and provide a thermochemically feasible mechanism to model the climatic impact of iodine-containing particles. In addition, we propose that a key iodine reservoir species such as iodine nitrate, which we observe as a product of the reaction between iodine oxides and the nitrate anion, can be also detected by CIMS in the atmosphere and has been potentially overlooked in previous field observations4.


1 Gómez Martín, J.C., et al. A gas-to-particle conversion mechanism helps to explain atmospheric particle formation through clustering of iodine oxides. Nat. Commun., 11, 4521, https://doi.org/10.1038/s41467-020-18252-8, 2020

2 Sipilä, M., et al. Molecular-scale evidence of aerosol particle formation via sequential addition of HIO3. Nature 537, 532–534, https://doi.org/10.1038/nature19314, 2016.

3 He et al., Role of iodine oxoacids in atmospheric aerosol nucleation, Science, 371, 589–595, https://doi.org/10.1126/science.abe0298, 2021.

4 Baccarini et al. Frequent new particle formation over the high Arctic pack ice by enhanced iodine emissions, Nat. Commun., 11, 4924, https://doi.org/10.1038/s41467-020-18551-0, 2020.

How to cite: Gomez Martin, J. C., Lewis, T. R., James, A. D., Plane, J. M. C., and Saiz-Lopez, A.: Ion-molecule reaction laboratory experiments show that iodine oxides explain CIMS atmospheric observations attributed to iodine oxoacids , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1452, https://doi.org/10.5194/egusphere-egu22-1452, 2022.

Lucia Iezzi et al.

Aerosols and clouds are complex systems containing organic and inorganic species, which play central roles in atmospheric chemistry and physics, climate, air pollution and public health. Particularly chemical reactions which occur in the aqueous phase can change the composition and oxidizing capacity of the troposphere via the production and release of trace gas species. Iron(III)-carboxylate complexes impact the chemistry of the atmospheric aqueous phase due to their photochemistry which can trigger free radical chemistry generating reactive oxygen species (ROS), such as HO2 and H2O2. Several studies have highlighted the importance of iodine chemistry due to its capability to influence both oxidative capacity and radiative balance of the atmosphere. A previous work of this group demonstrated a direct link between carbonyl compounds, ROS and iodine chemistry [1]. Furthermore, observed ratios of iodide to iodate in aerosol particles and cloud droplets of the troposphere are much higher than expected [2, 3]. This is indicative of active chemical recycling of iodine between the gas and particle phases, which may be driven by not well understood reductive processes involving iodate, which is thermodynamically the most favored iodine form in the aqueous phase under oxidizing conditions.

We performed coated wall flow tube experiments (CWFT) with aqueous films containing iodate and Iron(III)-citrate (fe-cit) using citric acid (CA) as a matrix since it is an established proxy for oxygenated atmospheric organic matter and with well characterized microphysical properties. The CWFT was coupled with a CE-DOAS instrument in order to detect I2 [4] resulting from iodate reduction. The results suggest that  photochemistry promotes efficient iodate reduction, linked to the photochemical turnover of the iron(III)-carboxylate complex and to the depletion of the iodine reservoir. We speculate that reduction of iodate is driven by H2O2 according to the Bray-Liebhafsky mechanism, where H2O2 is provided by fe-cit photochemistry. 

1. P. Corral Arroyo, et al., Atmospheric Chemistry and Physics, (2019)

2. A.R. Baker and C. Yodle, Atmos. Chem. Phys. Discuss., 2021, 1 (2021)

3. T.K. Koenig, et al., Sci Adv, 7, eabj6544 (2021)

4. R. Thalman, et al., Journal of Quantitative Spectroscopy and Radiative Transfer, 147, 171 (2014)

How to cite: Iezzi, L., Reza, M., Finkenzeller, H., Roose, A., Bartels-Rausch, T., Volkamer, R., and Ammann, M.: Iron(III)-carboxylate photochemistry induces iodate reduction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1922, https://doi.org/10.5194/egusphere-egu22-1922, 2022.

Markus Ammann et al.

Recently, Koenig et al. [1] measured both gas phase iodine species and particulate iodine (iodate and iodide) in the lower stratosphere indicating that tropospheric multiphase redox reactions prevent poorly soluble gaseous iodine species from removal by wet deposition leading to injections of inorganic iodine into the lower stratosphere. This may influence stratospheric ozone depletion both indirectly through activation of iodide (I-) to molecular halogens and directly through the aqueous phase reaction of ozone (O3) with iodide.  Also in the troposphere, measurements indicate higher than expected iodide to iodate ratios in the aerosol phase [2], suggesting the reaction of O3 with I- to be part of iodine cycling throughout the troposphere. The reaction of O3 with I- in the aqueous phase, leading to IO- and to I2 through the secondary reaction of IO- with I-, is rather well established and one of the main iodine source from oceans [3]. However, for the reaction in the aerosol phase, uncertainties exist with respect to the temperature dependence, effects of pH and ionic strength, and also the extent of a surface reaction pathway [4,5].  In addition, Sakamoto et al. [4] have suggested that from this reaction IO(g) may be released. The objectives of this work has been to determine the temperature dependence of the oxidation of I- by O3 as well as to have a better understanding of the parameters that lead to IO radical and I2 formation. We used a trough reactor [5] coupled to Cavity Enhanced – Differential Optical Absorption Spectroscopy (CE-DOAS) [6] to study the reactivity in dilute aqueous solution (273 – 291 K) and in concentrated ammonium sulfate solutions (255 – 291 K). Measurements at varying O3 mixing ratios indicate a substantial surface reaction component, especially at lower temperature. The IO/I2 ratio is in the range of 10-3 – 10-2. IO formation seems to result predominantly from a surface process. The experiments are also compared with results from theory.


[1]        T. K. Koenig et al., PNAS, 117, 4 (2020).

[2]        Baker, A. R., and Yodle, C.: Atmos. Chem. Phys., 21, 13067-13076, 2021.

[3]        L. J. Carpenter et al., Nat. Geosci., 6 (2013).

[4]        Y. Sakamoto et al., J. Phys. Chem. A, 113, 27 (2009).

[5]        C. Moreno et al., Phys. Chem. Chem. Phys., 22 (2020)

[6]        L. Artiglia et al., Nat. Commun., 8 (2017).

[7]        M. Wang et al., Atmos. Meas. Tech., 14, (2021).

How to cite: Ammann, M., Roose, A., Finkenzeller, H., Real, F., Vallet, V., Toubin, C., Gysin, S., Iezzi, L., and Volkamer, R.: IO radical yield from iodide oxidation by ozone on aqueous aerosol proxy surfaces, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5484, https://doi.org/10.5194/egusphere-egu22-5484, 2022.

Andrea Spolaor et al.

Polar stratospheric ozone has decreased since the 1970s due to anthropogenic emissions of chlorofluorocarbons and halons, resulting in the formation of an ozone hole over Antarctica. The effects of the ozone hole and the associated increase in incoming UV-radiation on terrestrial and marine ecosystems are well studied, however the impact on geochemical cycles of ice photoactive elements, such as iodine, remains almost unexplored. Here, we present the first iodine record from the inner Antarctic Plateau (Dome C) that covers approximately the last 212 years (1800-2012 CE). Our results show that iodine concentration in ice remained fairly constant during the pre-ozone hole period (1800-1974 CE) but has declined twofold since the onset of the ozone hole era (~1975 CE), closely tracking the total ozone evolution over Antarctica. Based on ice core observations, laboratory measurements and chemistry-climate model simulations, we propose that the iodine decrease since ~1975 is caused by enhanced iodine re-emission from snowpack due to the ozone hole driven increase in UV-radiation reaching the Antarctic Plateau. These findings suggest the potential for ice core iodine records from the inner Antarctic Plateau as an archive for past stratospheric ozone trends.

How to cite: Spolaor, A., Burgay, F., P. Fernandez, R., Turetta, C., Cuevas, C. A., Kim, K., Kinnison, D. E., Lamarque, J.-F., De Blasi, F., Barbaro, E., Corella, J. P., Vallelonga, P., Frezzotti, M., Barbante, C., and Saiz-Lopez, A.: Antarctic ozone hole modifies iodine geochemistry on the Antarctic Plateau, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3777, https://doi.org/10.5194/egusphere-egu22-3777, 2022.

Moritz Schöne et al.

Halogen radicals can drastically alter the atmospheric chemistry. In the polar regions, this is made evident by the ozone depletion in the stratosphere (ozone hole) but also by localized destruction of boundary layer ozone during polar springs. These recurrent episodes of catalytic ozone depletion, better known as “ozone depletion events” (ODEs) are caused by enhanced concentrations of reactive bromine compounds. The proposed mechanism by which these compounds are released into the troposphere is called “bromine explosion” - reactive bromine is formed autocatalytically from the condensed phase.

In comparison to previous satellite missions, the TROPOspheric Monitoring Instrument (TROPOMI) onboard ESA’s S5-P satellite allows for an improved localization and a more precise specification of these events due to its superior spatial resolution of up to 3.5 x 5.5 km2. Together with the better than daily coverage over the polar regions, this allows for investigations of the spatiotemporal variability of enhanced BrO levels and their relation to different possible bromine sources and release mechanisms.

We present tropospheric BrO column densities retrieved from TROPOMI measurements using Differential Optical Absorption Spectroscopy (DOAS). The advantage of our retrieval is its independence from any external input data. We used a modified k-means clustering and methods from statistical data analysis to separate tropospheric and stratospheric partial columns, thereby relying only on NO2 and O3 columns measured by the same instrument. This ensures in particular that the derived tropospheric BrO data set keeps the same spatial resolution as the TROPOMI instrument, because no model data with coarse resolution is used. In a second step, the BrO slant column densities (SCDs) are converted into vertical column densities (VCDs) by using an air mass factor (AMF). These AMFs are derived using a look-up table (LUT) generated by the McArtim radiative transfer model. From this LUT the AMF is calculated for each pixel using measured OSCDs and reflectance data. In a last step, satellite pixels are differentiated by their sensitivity to the lower troposphere using the determined AMF. This allows the exclusion of measurements deemed not sensitive to the troposphere from the dataset and gives a high confidence in the remaining retrieved values.

Our retrieval algorithm avoids systematic biases from external data sets and climatologies and is therefore particularly well suited to compare the retrieved VCDs to additional environmental parameters suspected to alter the release and distribution of BrO during Arctic spring. We examine tropospheric BrO enhancements through case studies, with particular emphasis on the interconnection of ODEs and meteorology. We focus here on the relation of tropospheric BrO to mean sea level pressure, surface air temperature, sea ice age and wind speed and direction. In addition, the spatiotemporal extent of events is studied and compared to WRF-Chem simulations.

How to cite: Schöne, M., Warnach, S., Borger, C., Herrmann, M., Gutheil, E., Beirle, S., Platt, U., and Wagner, T.: Analysis of environmental influences on tropospheric BrO in the Arctic using S5-P/TROPOMI measurements, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5449, https://doi.org/10.5194/egusphere-egu22-5449, 2022.

Bianca Zilker et al.

Bromine Explosion Events (BEEs) have been observed since the late 1990s in the Arctic and Antarctic during polar spring and play an important role in tropospheric chemistry. In a heterogeneous, autocatalytic, chemical chain reaction cycle, inorganic bromine is released from the cryosphere into the troposphere and depletes ozone often to below detection limit. Ozone is a source of the most important tropospheric oxidizing agent OH and the oxidizing capacity and radiative forcing of the troposphere are thus being impacted. Bromine also reacts with gaseous mercury, thereby facilitating the deposition of toxic mercury, which has adverse environmental impacts. Cold saline surfaces, such as young sea ice, frost flowers, and snow are likely bromine sources during BEEs. Different meteorological conditions seem to favor the development of these events: on the one hand, low wind speeds and a stable boundary layer, where bromine can accumulate and deplete ozone, and on the other hand, high wind speeds above approximately 10 m/s with blowing snow and a higher unstable boundary layer. In high wind speed conditions – occurring for example along fronts of polar cyclones – recycling of bromine on snow and aerosol surfaces may take place aloft.

To improve the understanding of weather conditions and bromine sources leading to the development of BEEs, case studies using high resolution S5P TROPOMI retrievals of tropospheric BrO together with meteorological simulations by the WRF model and Lagrangian transport simulations of BrO by FLEXPART-WRF are carried out. WRF simulations show, that high tropospheric BrO columns observed by TROPOMI often coincide with areas of high wind speeds. This probably points to release of bromine from blowing snow with cold temperatures favoring the bromine explosion reactions. However, some BrO plumes are observed over areas with very low wind speed and a stable low boundary layer.

In addition, BEEs over Ny-Ålesund and the prevailing weather conditions are examined. To monitor the amount of ozone depleted during BEEs, ozone sonde measurements from Ny-Ålesund were used. First evaluations show a drastic decrease in ozone, partly below the detection limit, while measuring enhanced BrO values at the same time. In order to analyze the origin of the BrO plumes observed in Ny-Ålesund, and to investigate transportation routes, FLEXPART-WRF runs are executed for the times of observed ozone depletion.


This work was supported by the DFG funded Transregio-project TR 172 “Arctic Amplification (AC)3“.

How to cite: Zilker, B., Blechschmidt, A.-M., Seo, S., Bougoudis, I., Bösch, T., Richter, A., and Burrows, J. P.: Investigation of weather conditions and tropospheric BrO transport during Bromine Explosion Events in the Arctic and ozone depletion in Ny-Ålesund observed by satellite and ground-based remote sensing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9667, https://doi.org/10.5194/egusphere-egu22-9667, 2022.

Shaddy Ahmed et al.

Polar halogen chemistry has long been known to be active, especially in spring, and has an important influence on the lifetime of some volatile organics, ozone, and mercury. Reactive chlorine and bromine species, produced from snow and aerosols, can have significant impacts on the oxidative capacity of the polar boundary layer. However, halogen production mechanisms from snow remain highly uncertain, making it challenging to include descriptions of halogen snow emissions in models and to understand the impact on atmospheric chemistry. In this work, we investigate the role of Arctic chlorine and bromine emissions from snow on boundary layer oxidation processes using a one-dimensional atmospheric chemistry and transport model (PACT-1D). We explore the impact of halogen snow emissions and boundary layer dynamics on atmospheric chemistry by modelling primary emissions of Cl2 and Br2 from snow, and heterogeneous recycling reactions on snow and aerosols. We present a two-day case study from the 2009 Ocean-Atmosphere-Sea Ice-Snowpack (OASIS) campaign at Utqiagvik, Alaska. 

The model reproduces both the diurnal cycle and high quantity of Cl2 measured, along with the observed concentrations of Br2, BrO, and HOBr. Due to a combination of chemical emissions, recycling, vertical mixing, and atmospheric chemistry, reactive chlorine is confined to the lowest 15 m of the atmosphere, whilst bromine impacts chemistry up to the boundary layer height. Following the inclusion of halogen emissions and recycling, HOx concentrations (HOx = OH+HO2) increase by as much as a factor of 30 at the surface at mid-day. Consequently, volatile organic compound (VOC) lifetimes are significantly reduced within a shallow layer near the surface, due to chlorine atoms from Cl2 snow emissions and increased HOx attributable to halogen chemistry.

How to cite: Ahmed, S., Thomas, J. L., Tuite, K., Stutz, J., Flocke, F., Orlando, J. J., Hornbrook, R. S., Apel, E. C., Emmons, L. K., Helmig, D., Boylan, P., Huey, L. G., Hall, S. R., Ullmann, K., Cantrell, C. A., and Fried, A.: Reactive halogen chemistry in the Arctic boundary layer over snow during spring: A 1D modelling case study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7516, https://doi.org/10.5194/egusphere-egu22-7516, 2022.

Simeng Li and Le Cao

The tropospheric Ozone Depletion Event (ODE), first observed at Barrow, Alaska (now known as Utqiagvik), is a phenomenon that occurs during the springtime of Arctic. During ODEs, the surface ozone declines rapidly from a background level of 40-60 ppbv to a few ppbv, within a couple of days or even hours. In the present study, we made a three-dimensional simulation of ODEs occurring during March 28 to April 5, 2019 at Barrow and its surrounding areas, using a 3-D multi-scale air quality model, CMAQ.

Three ODEs observed at Barrow were accurately captured in the model and analyzed thoroughly using the tool of process analysis. It was found that the first ODE occurred on March 29 was mostly caused by a transport of a low-ozone air to the west of the Chukchi Sea. In contrast, the occurrence of another ODE between March 30 and 31 is attributed to a horizontal transport of the ozone-lacking air from the Beaufort sea. This ozone-lacking air ascribes to a release of abundant sea-salt aerosols from the Bering Strait under a strong wind condition, resulted from a cyclone formed at the Chukotka Peninsula. Afterwards, bromine is activated from the sea-salt aerosols, consuming ozone over the sea. It was found that over the sea, the consumption of the surface ozone due to chemical processes reaches as large as 10 ppb. During this ODE, ozone drops to a level lower than 5 ppb. In contrast, BrO attains a maximum of approximately 100 ppt. This ozone-lacking air over the sea thus leads to the partial ODE occurring at Barrow through the horizontal transport. The third ODE occurring on April 2 was also found to be mainly caused by the horizontal advection from the sea. Later on, on April 3, ozone in the boundary layer is replenished by the strong vertical diffusion of ozone-rich air from the free troposphere, leading to the termination of this ODE. 

Our 3-D simulations also indicate that the vertical properties of the atmosphere exert a remarkable impact on the vertical distribution of chemical species. Under strong uplifting and warm underlying surfaces, the ozone-lacking air can break through the top of the boundary layer, affecting the free atmosphere. 

How to cite: Li, S. and Cao, L.: A three-dimensional simulation and process analysis of tropospheric Ozone Depletion Events (ODEs) during the springtime of Arctic using CMAQ, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-132, https://doi.org/10.5194/egusphere-egu22-132, 2022.

Rafael Pedro Fernandez et al.

Very Short-Lived (VSL) Halogens are primary organic compounds that are mainly emitted to the atmosphere from the biologically productive regions of the oceans, where the rapid and permanent vertical transport can uplift halogen-rich air-masses above the Marine Boundary Layer (MBL) well into the Free Troposphere (FT). Depending on the changes of convection strength, the regional distribution of oceanic sources, and the seasonality of the VSL photochemical losses, the release of inorganic halogen atoms from their initial organic sources due to reaction with OH and/or photolysis, can present a pronounced spatio-temporal variability. In addition, depending on the height and background where the initial inorganic halogen atoms are released, an additional atmospheric halogen source arising from the efficient halide uptake occurring over sea-salt aerosols (the so-called SSA-dehalogenation) enhances the total tropospheric halogen loading. Given the variable solubility and washout efficiency of the different gas-phase halogen species, considering their instantaneous partitioning, as well as their individual sinks for different in-cloud, below-cloud and clear-sky conditions, is of major importance to determine the total inorganic halogen budget within the MBL and FT. In this work, we present a modeling study performed with the state-of-the-art CAM-Chem model, oriented to determine the vertical, geographical and temporal distribution of the inorganic halogen sources and sinks on the global troposphere, distinguishing between the different regimes prevailing between tropical and high-latitude regions, as well as the distinctive behavior controlling the day/night and seasonal variability. A species-by-species inter-comparison for the VSL Chlorine, Bromine, Iodine families is presented, distinguishing the dominant sources, sinks and photochemical channels controlling the halogen burden at different heights, and highlighting the commonalities and differences existing among the chlorine, bromine and iodine families.

How to cite: Fernandez, R. P., Reynoso, A., Maldonado, A., Tomazzeli, O., Cremades, P., Berná, L., Lopez Noreña, A. I., Cuevas, C., Li, Q., and Saiz-Lopez, A.: Spatial and temporal variability of inorganic halogen sources and sinks over the marine boundary layer and free troposphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5165, https://doi.org/10.5194/egusphere-egu22-5165, 2022.

Qinyi Li et al.

Severe and persistent haze events in northern China, characterized by high loading of fine aerosol especially of secondary origin, negatively impact human health and the welfare of ecosystems. However, current knowledge cannot fully explain the formation of this haze pollution. Despite field observations of elevated levels of reactive halogen species (e.g., BrCl, ClNO2, Cl2, HBr) at several sites in China, the influence of halogens (particularly bromine) on haze pollution is largely unknown. Here, for the first time, we compile an emission inventory of anthropogenic bromine and quantify the collective impact of halogens on haze pollution in northern China. We utilize a regional model (WRF-Chem), revised to incorporate updated halogen chemistry and anthropogenic chlorine and bromine emissions and validated by measurements of atmospheric pollutants and halogens, to show that halogens enhance the loading of fine aerosol in northern China (on average by 21%) and especially its secondary components (~130% for secondary organic aerosol and ~20% for sulfate, nitrate, and ammonium aerosols). Such a significant increase is attributed to the enhancement of atmospheric oxidants (OH, HO2, O3, NO3, Cl, and Br) by halogen chemistry, with a significant contribution from previously unconsidered bromine. These results show that higher recognition of the impact of anthropogenic halogens shall be given in haze pollution research and air quality regulation.

How to cite: Li, Q., Fu, X., Peng, X., Wang, W., Badia, A., Fernandez, R. P., Cuevas, C. A., Mu, Y., Chen, J., Jimenez, J. L., Wang, T., and Saiz-Lopez, A.: Halogens enhance haze pollution in China, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4097, https://doi.org/10.5194/egusphere-egu22-4097, 2022.

Bastien Geil et al.

Halogens in volcanic plumes are important for both volcanic and environmental research. For example, changes in the composition of the volcanic plume can be an indication of changes in the activity of the volcano. In addition to entrained air components, volcanic plumes consist mainly of SO2, CO2, and H2O. However, HF, HCl and HBr are also significant constituents of volcanic emissions. A particularly interesting element in this context is bromine because of its atmospheric relevance, but also since BrO forms in the volcanic plume and, like SO2, can be determined spectroscopically using remote sensing techniques, making it ideal for monitoring and surveillance of volcanoes. However, to interpret and use BrO concentrations, we need a fully understanding of the formation and evolution of BrO in volcanic plumes. A step forward can be gained by measuring all relevant halogen species.

Currently, several methods are used to detect the various halogen compounds. Remote sensing methods exist for only a few so we use in-situ sampling methods such as diffusion separators, filter packs or aqueous alkali traps to collect reactive and total halogen species, respectively.

In this study, we will present the results of total fluorine, chlorine, bromine and sulfur as well as CO2 and their ratios between, for field campaigns at a closed volcanic system - Vulcano in September 2019 and October 2020 and at an open vent volcano Mt Etna in July 2021. The results will be discussed in the light of the different degassing activity and therefore different temperature and will be compared to earlier studies at Masaya, Nyamulagira and Etna.

How to cite: Geil, B., Gutiérrez, X., Karbach, N., Bobrowski, N., and Hoffmann, T.: Halogen measurements with in-situ sampling techniques: Studies at Vulcano and Mt. Etna (Italy), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9728, https://doi.org/10.5194/egusphere-egu22-9728, 2022.

Herizo Narivelo et al.

Volcanoes are known to be important emitters of atmospheric gases and aerosols, both through explosive eruptions and persistent quiescent degassing (von Glasow et al., 2009). The most abundant gases in volcanic emissions are H2O, CO2, SO2 and halogens (HCl, HBr, HF). In general, halogens play an important role in the atmosphere by modifying air composition and oxidizing capacity in the troposphere (von Glasow et al., 2004). The chemical processes occurring within the plume lead to the formation of BrO following the ‘bromine explosion’ mechanism as evidenced from both observations and modelling (e.g. Bobrowski et al., 2003; Roberts et al., 2009). Oxidized forms of bromine (BrO) are formed during daytime within the plume due to heterogeneous reactions of HBr on volcanic aerosols leading to ozone depletion. So far, modelling studies mainly focused on spatial scales ranging from 10m to ~1km and processes occurring within a few hours after eruption.

The objective of this study is to go a step further by analysing the impact at the regional scale namely over the whole Mediterranean basin of a single Mt Etna eruption event in December 2018. For this, we have further developed the MOCAGE model (Guth et al., 2016), a chemistry transport model run at a resolution of 0.2°× 0.2°, to quantify the impacts of the halogen species emitted by the volcano on air composition. We selected here the case of the eruption of Mt Etna around Christmas 2018 characterised by large amounts of emissions over several days.

The results show that MOCAGE represents the halogen chemistry in the volcanic plume quite well. The bromine-explosion cycle takes place during the day of the eruption, with a rapid increase in BrO concentration leading to a strong depletion in ozone and NO₂ concentrations across the Mediterranean as well as to changes in the air composition in particular for bromine compounds such as Br, HOBr, BrONO₂, Br2 and BrCl. Adding to this, BrO is formed again on the following day (25/12/2018) during daytime from the bromine reservoir species from night time leading to additional ozone depletion.

The comparison of the tropospheric columns of BrO and SO2 retrievals from the TROPOMI spaceborne instrument with the MOCAGE simulations shows that the tropospheric BrO and SO₂ columns have the same order of magnitude and that the locations of the simulated and observed plumes are overall in good agreement during the main eruption period and the following six days. The comparison shows also the similarity of the order of magnitude of the BrO/SO2 ratio between MOCAGE and TROPOMI, especially for the 25th of December 2018.

How to cite: Narivelo, H., Marécal, V., Hamer, P. D., Surl, L., Roberts, T., Pelletier, S., Lamotte, C., Bacles, M., Josse, B., Guth, J., Warnach, S., and Wagner, T.: Halogen chemistry in Mount Etna's volcanic plume in December 2018: Comparisons between 3D MOCAGE CTM simulations and TROPOMI satellite measurements, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2729, https://doi.org/10.5194/egusphere-egu22-2729, 2022.