AS3.23

Aside from capable of influencing atmospheric oxidation capacity, iodine species are known to contribute to particle formation processes. Iodine particle formation was commonly believed to be important in coastal regions only, e.g. Mace Head, but emerging evidence shows that it also plays an important role in Arctic regions.

Although the nucleation mechanisms have been proposed to involve mainly iodine oxides, recent field observations suggest that HIO₃ plays a key role in the cluster formation processes. Despite these advances, experiments with atmospherically relevant vapor concentrations are lacking and the time evolution of charged cluster formation processes has never been detected at the molecular level to validate the mechanisms observed in the field.

In this study, we carried out iodine particle formation experiments in the CLOUD chamber at CERN. The precursor vapor (I₂) and oxidation products were carefully controlled at concentrations relevant to those in marine boundary layer conditions. Natural galactic cosmic rays were used to produce ions in the chamber which further initiated ion-induced nucleation processes. An atmospheric pressure interface time-of-flight mass spectrometer was used to trace the time evolution of charged iodine clusters which revealed HIO₃ as the major contributor.

How to cite: He, X.-C., Iyer, S., Tham, Y. J., Sipilä, M., Kirkby, J., Kurtén, T., Kulmala, M., and collaboration, T. C.: Ion-induced iodic acid nucleation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10470, https://doi.org/10.5194/egusphere-egu21-10470, 2021.

Field observations of IO³⁻ and HIO³⁻-containing cluster anions by chemical ionization–atmospheric pressure interface–time-of-flight mass spectrometry (CI-API-ToF-MS) have been reported1. These observations, which employ nitrate (NO³⁻) reagent ions for reaction with the analytes, have been interpreted as resulting from atmospheric gas-phase iodic acid (HOIO₂) and molecular cluster formation via HOIO₂ addition steps. CI-API-ToF-MS chamber measurements with alternative ionization schemes have also reported signals that could be attributed to gas-phase HOIO and HOIO₂. However, well-established chemical kinetics and thermochemistry do not indicate any straightforward route to gas-phase iodine oxyacids and HOIO2 particle formation in the atmosphere. This does not only hinder the ability of chemical models for linking iodine emissions and particle formation, but also calls into question the interpretation of these CI-API-ToF-MS measurements. It has been proposed that water plays an important role in generating gas phase and HOIO₂-containing molecular clusters, but recent flow tube experiments have established extremely low upper limits to the rate constants of possible reactions between iodine oxides (IO_x and I_xO_y) and water. In this presentation, we discuss experimental and theoretical kinetics and thermochemistry of proposed routes to gas-phase HOIO and HOIO₂ in the atmosphere as well as potential ion-molecule reactions turning iodine oxides into IO^3- ions in the CI-API-ToF-MS inlet. We show that there is an important ambiguity in the interpretation of IO^3- and other signals observed with CI instruments as a result of barrierless reactions between I_xO_y and the reagent ions. Experiments for solving this ambiguity and reconciling conflicting results are proposed.

How to cite: Lewis, T., Gomez Martin, J. C., Blitz, M., Saiz-Lopez, A., and Plane, J.: Are iodic acid measurements by chemical ionization unambiguous? , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13817, https://doi.org/10.5194/egusphere-egu21-13817, 2021.

Iodine in the atmosphere results from emissions of precursors from the oceans [1, 2] and undergoes continuous multiphase cycling. This cycling also prevents poorly soluble gaseous iodine species from removal by wet deposition. Thus, tropical convective outflow can even inject inorganic iodine into the lower stratosphere [3]. In the troposphere [1] and in the stratosphere [4], iodine appears in the gas- and particulate phase. In both compartments, particulate iodine exists not only in oxidized (as iodate) but also in reduced (as iodide) form [1, 4]. As iodide reacts with ozone in the aqueous phase [2] (which is also a major process related to iodine emission from the oceans), the reaction of ozone with iodide is one wheel of the cycles in the troposphere and may even represent a direct ozone sink in the stratosphere. However, only few kinetic data exist for this reaction. The temperature dependence of the reaction rate coefficient between 275 and 293 K was determined once and extrapolation of its value below 275 K rely on an activation energy estimate with an error of about 40 % [5]. Therefore, we performed laboratory experiments to extend the temperature range of the rate coefficient determination. We used a trough flow reactor [6] for our measurements and analyzed the data with a quasi steady state resistance model [7] to determine the essential physical parameters describing the reaction kinetics and their temperature dependence. Our results help to increase the understanding of atmospheric iodine chemistry and to better assess iodine’s impact on ozone in both, the troposphere and the stratosphere.

Bibliography
[1]          A. Saiz-Lopez et al., Chem. Rev., 112, 3 (2012)
[2]          L. J. Carpenter et al., Nat. Geosci., 6 (2013)
[3]          A. Saiz-Lopez et al., Geophys. Res. Lett., 42, 16 (2015)
[4]          T. K. Koenig et al., PNAS, 117, 4 (2020)
[5]          L. Magi et al., J. Phys. Chem. A, 101 (1997)
[6]          L. Artiglia et al., Nat. Commun., 8 (2017)
[7]          M. Ammann et al., Atmos. Chem. Phys., 13 (2013)

How to cite: Gysin, S., Roose, A., Volkamer, R., Peter, T., and Ammann, M.: Temperature dependent kinetics of the reaction of ozone with iodide, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10032, https://doi.org/10.5194/egusphere-egu21-10032, 2021.

Every year during polar sunrise, a series of photochemical events are observed episodically in the troposphere over the Arctic and Antarctic, including bromine explosion events (BEEs), ozone depletion events (ODEs), and mercury depletion events (MDEs). Extensive studies show that all these events are triggered by gas-phase reactive bromine species that are photochemically activated from sea-salt bromide via multi-phase reactions under freezing air temperatures. However, major knowledge gaps exist in both fundamental cryo-photochemical processes and local meteorological conditions that may affect the timing and magnitude of those events. Here, we present an outdoor mesocosm-scale experiment in which we studied the depletion of surface ozone and gaseous elemental mercury at the Sea-ice Environmental Research Facility (SERF) in Winnipeg, Canada, in an urban and non-polar region. Temporal changes in ozone and gaseous elemental mercury concentrations inside acrylic tubes were monitored over bromide-enriched artificial seawater during entire sea ice freeze-and-melt cycles and open water periods. Mid-day photochemical loss of both gas species was observed in the boundary layer air immediately above the sea ice surface, in a pattern that is characteristic of BEE-induced ODEs and MDEs in the Arctic. The importance of UV radiation and sea ice presence in causing such observations was demonstrated by sampling from UV-transmitting and UV-blocking acrylic tubes under different air temperatures. The ability of reproducing mesocosm-scale BEE-induced ODEs and MDEs in a non-polar region provides a new platform with opportunities to systematically study the cryo-photochemical mechanisms leading to BEEs, ODEs, and MDEs in the Arctic, their role in biogeochemical cycles across the ocean-sea ice-atmosphere interfaces, and their sensitivities to a changing climate. 

How to cite: Gao, Z., Wang, F., and Geilfus, N.-X.: Reproducing polar springtime bromine explosion events, ozone depletion events and atmospheric mercury depletion events in an outdoor mesocosm sea-ice facility, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6296, https://doi.org/10.5194/egusphere-egu21-6296, 2021.

Mercury is transported globally through the atmosphere as atomic mercury, but mostly it is transferred from the atmosphere to ecosystems in the form of Hg(II) compounds. As a result, scientists are increasingly focused on oxidation-reduction chemistry of mercury in the atmosphere. At present, little is known about the interaction of mercury compounds with environmental surfaces, which commonly possess adsorbed water.

As a first step towards understanding these interactions, we have theoretically studied the reaction of BrHgO• + CO → BrHg• + CO₂, which constitutes a potentially important mercury reduction reaction in the atmosphere. We characterized the potential energy surface with CCSD(T)/CBS energies (with corrections for relativistic effects) at MP2 geometries. Master Equation simulations were used to reveal the factors controlling the overall rate constant.

In a second step and for the first time, the monohydration of several oxygenated mercury-containing compounds (BrHgO, BrHgOH, BrHgOOH, BrHgNO₂ and its isomers, and HgOH) with one water molecule has been theoretically studied using the ωB97X-D/aug‐cc‐pVTZ level of theory. The thermodynamic properties of the hydration reactions have been calculated using DFT geometries with energies with coupled-cluster calculations DK-CCSD(T) and the ANO‐RCC‐Large basis sets. Standard reaction enthalpy and standard Gibbs free reaction energy were computed. The temperature dependences of Δ_rG°(T) were evaluated for all studied aggregates over the temperature range 200 - 400 K. For the first time, the monohydration processes have been studied to elucidate the role of hydrating water molecules. Atmospheric implications have been discussed.

How to cite: Taamalli, S., Louis, F., Pitonak, M., Cernusak, I., and Dibble, T. S.: Atmospheric chemistry of oxygenated mercury-containing compounds, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5839, https://doi.org/10.5194/egusphere-egu21-5839, 2021.

Alkyl hydroperoxides are essential intermediates in the atmospheric oxidation of hydrocarbons and in low-temperature combustion processes [1]. Chlorinated alkyl hydroperoxides play a similar role in the atmospheric oxidation of chlorinated hydrocarbons. It is important to study the thermodynamic parameters for these species to understand and predict the reaction pathways, rate constants, and equilibrium constants. There are relatively few experimental studies on the thermodynamic properties of alkyl hydroperoxides due to their rapid interconversion and instability, which makes the studies of these species complex.

The main objective of this work is to provide reliable kinetic and thermodynamic data for the gas phase reaction of hydroxyl radicals with chloromethyl hydroperoxyl (CH₂ClOOH). Several possible reaction pathways could be feasible: H-abstraction, Cl-abstraction, and OH-abstraction. The reaction mechanism involves many stationary points on the potential energy surface and reveals some unusual features for the H-abstraction. Theoretical calculations were performed with the augmented correlation consistent basis sets aug-cc-pVTZ for H and O atoms and the aug-cc-pV(T+d)Z for Cl atom including tight d polarization functions. The potential energies have been calculated at the DK-CCSD(T)/ANO-RCC (VTZP and VQZP) level of theory on the geometries optimized previously.

Implications for atmospheric chemistry are presented and discussed.

References

[1] H. Sun, C. Chen, and J. Bozzelli, “Structures, Intramolecular Rotation Barriers, and Thermodynamic Properties (Enthalpies, Entropies and Heat Capacities) of Chlorinated Methyl Hydroperoxides (CH₂ClOOH, CHCl₂OOH, and CCl₃OOH)”, The Journal of Physical Chemistry A, 2000; 104 (35): 8270-8282, https://doi.org/10.1021/jp0013917

How to cite: Srour, Z., Taamalli, S., Fèvre-Nollet, V., Marécal, V., Cernusak, I., and Louis, F.: Investigation of the reaction OH+CH2ClOOH of atmospheric interest, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5605, https://doi.org/10.5194/egusphere-egu21-5605, 2021.

Laboratory experiments are presented on the phase change at the surface of sodium chloride – water mixtures at temperatures between 259 K and 240 K. Chloride is a ubiquitous component of polar coastal surface snow. The chloride embedded in snow is involved in reactions that modify the chemical composition of snow as well as ultimately impact the budget of trace gases and the oxidative capacity of the overlying atmosphere.  Multiphase reactions at the snow – air interface have found particular interest in atmospheric science. Undoubtedly, chemical reactions proceed faster in liquids than in solids; but it is currently unclear when such phase changes occur at the interface of snow with air.

In the experiments reported here, a high selectivity to the upper few nanometres of the frozen solution – air interface is achieved by using electron yield near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. We find that sodium chloride at the interface of frozen solutions, which mimic sea-salt deposits in snow, remain as supercooled liquid down to 240 K, which is about 10 K lower than the freezing temperature of sodium chloride solutions. Below this temperature, hydrohalite exclusively precipitates, anhydrous sodium chloride is not detected. In this work, we present the first NEXAFS spectrum of hydrohalite. The hydrohalite is found to be stable while increasing the temperature towards the eutectic temperature of 253 K.

Taken together, this study reveals no differences in the phase changes of sodium chloride at the interface as compared to the bulk. That sodium chloride remains liquid at the interface upon cooling down to 240 K, which spans the most common temperature range in Polar marine environments, has consequences for interfacial chemistry involving chlorine as well as for any other reactant for which the sodium chloride provides a liquid reservoir at the interface of environmental snow. Implications for the role of surface snow on atmospheric chemistry are discussed. 

How to cite: Bartels-Rausch, T., Kong, X., Orlando, F., Artiglia, L., Waldner, A., Huthwelker, T., and Ammann, M.: Supercooled liquid sodium chloride solution on ice and snow surfaces, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2202, https://doi.org/10.5194/egusphere-egu21-2202, 2021.

Volcanic plumes are known to contain reactive halogen species, especially bromine oxide. Therefore, local ozone (O₃) depletion (OD) is expected inside volcanic plumes. This OD has been measured in several field studies and is also found in several modelling studies. Recently, in order to quantify O₃ mixing ratios in volcanic plumes, mainly UV absorption monitors have been used as these have become the standard technique for ambient O₃ monitoring. However, these instruments show a large positive interference with sulphur dioxide (SO₂). In fact, these instruments are approximately only 100 times more sensitive to O₃ than to SO₂. This poses a significant problem for volcanic measurements since SO₂ mixing ratios can exceed O₃ mixing ratios by factors of 1000 or more. Thus, laborious SO₂ filtering introducing further problems, as e.g. humidity dependence, needed to be employed.

In this work simultaneous O₃ measurements inside a fumarole were conducted with a compact and mobile (backpack-size, ~10kg) chemiluminescence (CL) ozone monitor and a conventional UV absorption monitor at the summit of Mt Etna volcano, Italy. In parallel, SO₂ and CO₂ measurements were carried out with a MultiGAS-instrument. The CL monitor was used since no interference from trace gases contained in volcanic plumes is expected. Indeed, in this first field study inside a fumarole, we observed no significant interference with volcanic SO₂ concentrations for the CL monitor. Under field conditions the CL monitor’s detection limit was determined to be ~1 ppb (1σ) at an integration time of 1 second.

Additionally, a rough calculation to estimate the expected OD in volcanic plumes was made. Contrary to popular belief, this calculation suggests for typical bromine oxide concentrations no significant (i.e. <1%) reactive halogen catalysed O₃-loss in volcanic plumes.

How to cite: Rüth, M., Fuchs, C., Kuhn, J., Bobrowski, N., Platt, U., and Schmitt, S.: Is there an ozone depletion in volcanic plumes?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1040, https://doi.org/10.5194/egusphere-egu21-1040, 2021.

Reactive iodine plays a key role in determining the oxidation capacity of the atmosphere in addition to being implicated in the formation of new particles in the marine environment. Recycling of reactive iodine from heterogeneous processes on sea-salt aerosol was hypothesized over two decades ago but the understanding of this mechanism has been limited to laboratory studies and has not been confirmed in the atmosphere until now. Here, we report the first direct ambient observations of hypoiodous acid (HOI) and heterogeneous recycling of iodine monochloride (ICl) and iodine monobromide (IBr) at Mace Head Observatory in Ireland (53°19’ N, 9°54’ W) during the summer of 2018. A newly developed bromide based chemical ionization atmospheric pressure interface time-of-flight mass spectrometer (Br-CI-APi-TOF) was deployed to measure I₂, HOI, ICl, and IBr. Significant levels of ICl and IBr, with mean daily maxima of 4.3 and 3.0 pptv (1 min-average), respectively, have been observed throughout the campaign. We show that the heterogeneous reaction of HOI on marine aerosol and subsequent production of iodine interhalogens (ICl and IBr) are much faster than previously thought. These results indicate that the fast formation of iodine interhalogens, together with their rapid photolysis, results in more efficient recycling of atomic iodine than currently estimated by the models. The photolysis of the observed ICl and IBr leads to 32% increase in the daytime average of atomic iodine production rate, thereby enhancing the average daytime iodine-catalyzed ozone loss rate by 10-20%. Our findings provide the first direct field evidence that the autocatalytic mechanism of iodine release from marine aerosol is important in the atmosphere and can have significant impacts on atmospheric oxidation capacity and new particle formation in the troposphere.

How to cite: Tham, Y. J., He, X.-C., Li, Q., Cuevas, C. A., Ceburnis, D., Maier, N. M., O’Dowd, C., Dal Maso, M., Saiz-Lopez, A., and Sipilä, M. and the Mace Head Study Team: Field evidence of autocatalytic iodine release from atmospheric aerosol, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10593, https://doi.org/10.5194/egusphere-egu21-10593, 2021.

Bromine compounds play an important role in atmospheric chemistry with respect to ozone chemistry and the resulting oxidation capacity. Large amounts of reactive bromine can be released by an autocatalytic heterogeneous mechanism called “bromine explosion”, and plumes of enhanced bromine monoxide (BrO) have been observed over polar sea ice regions by satellite measurements in spring. These enhancements of BrO columns result from increases in stratospheric or tropospheric bromine columns or both. As nadir-viewing UV-visible spectrometers have limited vertical resolution, it is not straight-forward to separate total BrO columns into tropospheric and stratospheric partial columns using satellite data.

In this study, an algorithm for tropospheric BrO retrieval from satellite measurements including TROPOMI, which provides much improved spatial resolution, was developed. The retrieval algorithm is based on the Differential Optical Absorption Spectroscopy (DOAS) technique and three different stratospheric correction methods were tested based on: output from a 3D atmospheric chemistry model, a climatology of stratospheric BrO profiles, and an empirical multiple linear regression model to separate the tropospheric partial column from the total column.

Retrieved tropospheric BrO columns from satellite measurements were compared with ground-based MAX-DOAS BrO observations at the NDACC station in Ny-Ålesund. The comparisons between ground-based and satellite measurements of tropospheric BrO show good agreement in both time-series and scatter plots, demonstrating the satellite retrieval algorithm is valid and applicable to study bromine release in the tropospheric layer. In particular, TROPOMI shows improved validation results for short distance collection compared to previous satellite data, which suggests the applicability of high-resolution satellite data on small-scale bromine explosion events observed during the MOSAiC campaign.

How to cite: Seo, S., Richter, A., Blechschmidt, A.-M., Bougoudis, I., Wittrock, F., Bösch, T., and Burrows, J. P.: Retrieval of tropospheric BrO columns from TROPOMI and their validation using MAX-DOAS measurements in Ny-Ålesund, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10293, https://doi.org/10.5194/egusphere-egu21-10293, 2021.

Within the framework of the International Arctic Systems for Observing the Atmosphere (IASOA), we report a modelling-based study on surface ozone across the Arctic. We use surface ozone from six sites: Summit (Greenland), Pallas (Finland), Barrow (USA), Alert (Canada), Tiksi (Russia), and Villum Research Station (VRS) at Station Nord (North Greenland, Danish Realm), and ozonesonde data from three Canadian sites: Resolute, Eureka, and Alert. Two global chemistry models: a global chemistry transport model (p-TOMCAT) and a global chemistry climate model (UKCA), are used for model-data comparisons. Remotely sensed data of BrO from the GOME-2 satellite instrument at Eureka, Canada are used for model validation.

The observed climatology data show that spring surface ozone at coastal Arctic is heavily depleted, making ozone seasonality at Arctic coastal sites distinctly different from that at inland sites. Model simulations show that surface ozone can be greatly reduced by bromine chemistry. In April, bromine chemistry can cause a net ozone loss (monthly mean) of 10-20 ppbv, with almost half attributable to open-ocean-sourced bromine and the rest to sea-ice-sourced bromine. However, the open-ocean-sourced bromine, via sea spray bromide depletion, cannot by itself produce ozone depletion events (ODEs) (defined as ozone volume mixing ratios VMRs < 10 ppbv). In contrast, sea-ice-sourced bromine, via sea salt aerosol (SSA) production from blowing snow, can produce ODEs even without bromine from sea spray, highlighting the importance of sea ice surface in polar boundary layer chemistry.

Modelled total inorganic bromine (Br_Y) over the Arctic sea ice  is sensitive to model configuration, e.g., under the same bromine loading, Br_Y in the Arctic spring boundary layer in the p-TOMCAT control run (i.e., with all bromine emissions) can be 2 times that in the UKCA control run. Despite the model differences, both model control runs can successfully reproduce large bromine explosion events (BEEs) and ODEs in polar spring. Model-integrated tropospheric column BrO generally matches GOME-2 tropospheric columns within ~50% in UKCA and a factor of 2 in p-TOMCAT. The success of the models in reproducing both ODEs and BEEs in the Arctic indicates that the relevant parameterizations implemented in the models work reasonably well, which supports the proposed mechanism of SSA production and bromide release on sea ice. Given that sea ice is a large source of SSA and halogens, changes in sea ice type and extent in a warming climate will influence Arctic boundary layer chemistry, including the oxidation of atmospheric elemental mercury. Note that this work dose not necessary rule out other possibilities that may act as a source of reactive bromine from sea ice zone.

How to cite: Yang, X., Blechschmidt2, A.-M., Bognar, K., McClure–Begley, A., Morris, S., Petropavlovskikh, I., Richter, A., Skov, H., Strong, K., Tarasick, D., Utall, T., Vestenius, M., and Zhao, X.: Pan-Arctic surface ozone seasonality modified by sea-ice-sourced bromine: modelling vs measurements, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1262, https://doi.org/10.5194/egusphere-egu21-1262, 2021.

Halogen halides emitted by volcanoes are known to rapidly convert within plumes into BrO while depleting ozone, as clearly shown by observations and models over the past 2 decades (e.g. review by Gutmann et al., 2018). So far, most of the modelling studies have focused on the plume processes occurring in the first few hours after the emission. The only study at the regional scale is that of Jourdain et al. (2016). They assessed the impact of volcanic halogens for a period of strong degassing of the Ambrym volcano, showing in particular its effect on the atmospheric oxidizing capacity and methane lifetime.

A step further would be to quantify the impact of volcanic halogens at the global scale using global chemistry models. This type of model uses a horizontal resolution (greater than 50 km) that is much coarser than the plume size. This raises the issue of, whether at this resolution, it is possible to represent the chemistry occurring under high concentrations within the plume. To assess this, a sub-grid scale parameterization is proposed. It has been tested in the 1D version of MOCAGE global and regional chemistry transport model for a short eruption of Mt Etna on the 10^th of May 2008. The results show that while using the subgrid-scale plume parameterization or not does change the timing of when the maximum BrO occurs but does not affect the predicted maximum concentration. The same finding is made when using a range of different settings in the parameterization regarding dilution of the plume with its environment. The 1D model results show a sensitivity of BrO formation to parameters other than the sub-grid scale effects: composition of the plume at the vent, injection height of the emissions, and time of the day when the eruption takes place.

How to cite: Marécal, V., Voisin-Pessis, R., Roberts, T., Hamer, P., Aiuppa, A., Guth, J., and Narivelo, H.: Sub-grid scale representation of halogen chemistry in volcanic plumes based on 1D MOCAGE model simulations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1332, https://doi.org/10.5194/egusphere-egu21-1332, 2021.

Volcanoes emit different gaseous species, SO₂ and in particular halogen species especially bromine and chlorine compounds. In general, halogens play an important role in the atmosphere by contributing to ozone depletion in the stratosphere (WMO Ozone assessment, 2018) and by modifying air composition and oxidizing capacity in the troposphere (Von Glasow et al. 2004). The halogen species emitted by volcanoes are halides. The chemical processing occurring within the plume leads to the formation of BrO from HBr following the ‘bromine explosion’ mechanism as evidenced from both observations and modelling (e.g., Bobrowski et al. Nature, 2003; Roberts et al., Chem. Geol. 2009). Oxidized forms of chlorine and bromine are modelled to be formed within the plume due to the heterogenous reaction of HOBr with HCl and HBr, forming BrCl and Br₂ that photolyses and produces Br and Cl radicals. So far, modelling studies were mainly focused on the very local scale and processes occurring within a few hours after eruption.

In this study, the objective is to go a step further by analyzing the impact at the regional scale over the Mediterranean basin of a Mt Etna eruption event. For this, we use the MOCAGE model (Guth et al., GMD, 2016), a chemistry transport model run with a resolution of 0.2°x 0.2°, to quantify the impacts of the halogens species emitted by the volcano on the tropospheric composition. We have selected here the case of the eruption of Mount Etna around Christmas 2018 characterised by large amounts of emissions over several days (Calvari et al., remote sensing 2020; Corrdadini et al., remote sensing 2020). The results show that MOCAGE represents rather well the chemistry of the halogens in the volcanic plume because it established theory of plume chemistry. The bromine explosion process takes place on the first day of the eruption and even more strongly the day after, with a rapid increase of the in-plume BrO concentrations and a corresponding strong reduction of ozone and NO2 concentrations.

We also compared MOCAGE results with the WRF-CHEM model simulations for the same case study. We note that the tropospheric column of BrO and SO₂ in the two models have the same order of magnitude with more rapid bromine explosion occurring in WRF-CHEM simulations. Finally, we compared the MOCAGE results to tropospheric columns of BrO and SO₂ retrieved from TROPOMI spaceborne instrument.

How to cite: Narivelo, H., Marécal, V., Hamer, P. D., Surl, L., Roberts, T., Bacles, M., Warnach, S., and Wagner, T.: Using the 3D MOCAGE CTM to simulate the chemistry of halogens in the volcanic plume of Etna's eruption in December 2018 at the regional scale, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12205, https://doi.org/10.5194/egusphere-egu21-12205, 2021.

Ocean-going ships supply products from one region to another and contribute to the world’s economy. Ship exhaust contains many air pollutants and results in significant changes in marine atmospheric composition. The role of Reactive Halogen Species (RHS) in the troposphere has received increasing recognition and oceans are the largest contributors to their atmospheric burden. However, the impact of shipping emissions on RHS and that of RHS on ship-originated air pollutants have not been studied in detail. Here, an updated WRF-Chem model is utilized to explore the chemical interactions between ship emissions and oceanic RHS over the East Asia seas in summer. The emissions and resulting chemical transformations from shipping activities increase the level of NO and NO₂ at the surface, increase O₃ in the South China Sea, but decrease O₃ in the East China Sea. Such changes in pollutants result in remarkable changes in the levels of RHS as well as in their partitioning. The abundant RHS, in turn, reshape the loadings of air pollutants and those of the oxidants with marked patterns along the ship tracks. We, therefore, suggest that these important chemical interactions of ship-originated emissions with RHS should be considered in the environmental policy assessments of the role of shipping emissions in air quality and climate.

How to cite: Li, Q., Badia, A., Fernandez, R. P., Mahajan, A. S., López-Noreña, A. I., Zhang, Y., Wang, S., Puliafito, E., Cuevas, C. A., and Saiz-Lopez, A.: Chemical interactions between ship-originated air pollutants and ocean-emitted halogens, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10827, https://doi.org/10.5194/egusphere-egu21-10827, 2021.