Displays

Trace iodine vapours have a significant impact on atmospheric chemistry, influencing catalytic ozone destruction and the HO_x / NO_x cycles. Oxidized iodine species also form aerosols in coastal and polar regions (O’Dowd et al, 2002), playing a direct role in Earth’s radiation balance. It was recently shown that iodic acid (HIO₃) has a significant impact on coastal new particle formation processes (Sipilä et al., 2016). However, neutral HIO₃ molecules have only been measured in two sites (Sipilä et al., 2016).

In this study, a global observation of HIO₃ has been carried out in ten sites around the globe, including city sites, Arctic and Antarctica sites, a remote island site, a coastal site and a boreal forest site. While the existence of HIO₃ is unambiguously revealed in all of the sites, its concentration varies significantly among them. Dedicated laboratory experiments are required to examine the particle formation rates from iodine-containing species to be able to predict their global importance in particle formation, and further, in cloud condensation nuclei formation.

O’Dowd, C. D. et al. Marine aerosol formation from biogenic iodine emissions. Nature 417, 632–6 (2002)

Sipilä, M. et al. Molecular-scale evidence of aerosol particle formation via sequential addition of HIO₃. Nature 537, 532–534 (2016).

How to cite: He, X., Jokinen, T., Sarnela, N., Beck, L., Junninen, H., Rissanen, M., Nie, W., Yan, C., Kemppainen, D., Worsnop, D., Sipilä, M., and Kulmala, M.: Global observation of iodic acid (HIO3), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19391, https://doi.org/10.5194/egusphere-egu2020-19391, 2020.

The photooxidation of gas phase iodine-bearing molecules emitted by marine biota leads to intense particle nucleation events in the coastal and polar marine boundary layer^1-3. The ubiquity of iodine in the marine atmospheric environment^4-7 has suggested that this may be a previously unrecognized global source of new aerosol particles⁸. Atmospheric modeling is required in order to evaluate the importance of this process, but a substantial lack of understanding of the gas-to-particle conversion mechanism is hindering this effort, especially regarding the gas phase chemistry of the nucleating molecules (iodine oxides^9,10 and/or oxyacids⁷) and the formation kinetics of molecular clusters. To address this problem, we have conducted new flow tube laboratory experiments where pulsed laser photolysis or continuous broad-band photolysis of I₂/O₃ mixtures  in air are used to generate iodine radicals in the presence of atmospherically representative mixing ratios of water vapor. The molecular reactants and the resulting molecular products are detected by time-resolved VUV laser photo-ionization time-of-flight mass spectrometry. High-level quantum chemistry and master equation calculations and gas kinetics modelling are used to analyse the experimental data. In this presentation we discuss our results and their implications for the interpretation of field meassurements and for the implementatiion of an iodine oxide particle formation mechanism in atmospheric models.

References:

1. Hoffmann, T., O'Dowd, C. D. & Seinfeld, J. H. Iodine oxide homogeneous nucleation: An explanation for coastal new particle production. Geophys. Res. Lett. 28, 1949-1952 (2001).

2. McFiggans, G. et al. Direct evidence for coastal iodine particles from Laminaria macroalgae - linkage to emissions of molecular iodine. Atmos. Chem. Phys. 4, 701-713 (2004).

3. O'Dowd, C. D. et al. Marine aerosol formation from biogenic iodine emissions. Nature 417, 632-636 (2002).

4. Prados-Roman, C. et al. Iodine oxide in the global marine boundary layer. Atmos. Chem. Phys. 15, 583-593, doi:10.5194/acp-15-583-2015 (2015).

5. Schönhardt, A. et al. Simultaneous satellite observations of IO and BrO over Antarctica. Atmos. Chem. Phys. 12, 6565-6580, doi:10.5194/acp-12-6565-2012 (2012).

6. Mahajan, A. S. et al. Concurrent observations of atomic iodine, molecular iodine and ultrafine particles in a coastal environment. Atmos. Chem. Phys. 10, 27227-27253 (2010).

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

8. Saiz-Lopez, A. et al. Atmospheric Chemistry of Iodine. Chem. Rev. 112, 1773–1804, doi:DOI: 10.1021/cr200029u (2012).

9. Gómez Martín, J. C. et al. On the mechanism of iodine oxide particle formation. Phys. Chem. Chem. Phys. 15, 15612-15622, doi:10.1039/c3cp51217g (2013).

10. Saunders, R. W., Mahajan, A. S., Gómez Martín, J. C., Kumar, R. & Plane, J. M. C. Studies of the Formation and Growth of Aerosol from Molecular Iodine Precursor. Z. Phys. Chem. 224, 1095-1117 (2010).

How to cite: Gomez Martin, J. C., Lewis, T., Kumar, M., Plane, J., Francisco, J., and Saiz-Lopez, A.: The first steps of iodine gas-to-particle conversion as seen in the lab: constraints on the role of iodine oxides and oxyacids, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2870, https://doi.org/10.5194/egusphere-egu2020-2870, 2020.

Atomic chlorine radicals are known to affect atmospheric oxidation and pollutant lifetimes, but are challenging to detect due to their low ambient concentrations.  A lack of field observations limits useful assessments of the impacts of tropospheric chlorine oxidation on important atmospheric processes, such as regional ozone production, reactive nitrogen loss, and global methane removal.  In the last decade, instrumental innovations have enabled detection and speciation of much more stable chlorine atom reservoir species, such as nitryl chloride, through techniques such as cavity ring down spectroscopy and mass spectrometry.  HCl is the most abundant and long-lived tropospheric chlorine reservoir species, yet few observations exist.  Here, we present a specific method for detection of HCl via Tunable Laser Infrared Direct Absorption Spectrometer (TILDAS), which has been further extended for the detection of nitryl chloride.  This analytical method has several advantages over current observational techniques (e.g. chemical ionisation mass spectrometry), and will provide a much needed constraint on the tropospheric chlorine atom budget.

How to cite: Halfacre, J., Edwards, P., Herndon, S., Roscioli, J., Dyroff, C., Yacovitch, T., Marsden, N., Bannan, T., Percival, C., Coe, H., Veres, P., and Brown, S.: A novel spectroscopic approach for detection of chlorine reservoir species: HCl-TILDAS, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16783, https://doi.org/10.5194/egusphere-egu2020-16783, 2020.

Bromine atoms play a central role in atmospheric reactive halogen chemistry, depleting ozone and elemental mercury, thereby enhancing deposition of toxic mercury, particularly in the Arctic near-surface troposphere. Yet, direct bromine atom measurements have been missing to date, due to the lack of analytical capability with sufficient sensitivity for ambient measurements. Here we present direct atmospheric bromine atom measurements, conducted in the springtime Arctic near Utqiagvik, Alaska in March 2012. Measured bromine atom levels reached up to 14 ppt (4.2×10⁸ atoms cm^-3) and were up to 3-10 higher than estimates using previous indirect measurements not considering the critical role of molecular bromine. Observed ozone and elemental mercury depletion rates are quantitatively explained by the measured bromine atoms, providing field validation of highly uncertain mercury chemistry. Following complete ozone depletion, elevated bromine concentrations are sustained by photochemical snowpack emissions of molecular bromine and nitrogen oxides, resulting in continued atmospheric mercury depletion. This study shows that measured bromine atoms, resulting from photochemical snowpack production of molecular bromine, can quantitatively explain ozone and mercury loss in the near-surface polar atmosphere.

How to cite: Pratt, K., Wang, S., McNamara, S., Moore, C., Obrist, D., Steffen, A., Shepson, P., Staebler, R., and Raso, A.: Direct Detection of Atmospheric Atomic Bromine Leading to Mercury and Ozone Depletion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9439, https://doi.org/10.5194/egusphere-egu2020-9439, 2020.

The Rann of Kachchh is a salt desert in the southern border area of India and Pakistan. Recently, high amounts of bromine monoxide (BrO) were observed there in satellite measurements of the Ozone Monitoring Instrument (OMI). Release mechanisms of reactive bromine, dominating chemical processes, the influence of the ambient atmosphere and transport processes, etc. are not well understood in general. Furthermore, due to their short time scales these processes are difficult to assess with satellite instruments, which only offer a single measurement per day with limited spatial resolution.

Here, we present BrO, HCHO and nitrogen dioxide (NO₂) measurements from ground-based MAX DOAS performed at two different locations in the Rann of Kachchh salt desert in Gujarat, India during three weeks in March and April 2019. We observe large amounts of BrO building up during daytime reaching maxima of several tens of ppt in the late afternoon. Additional mobile measurements performed directly over the salt gave similar results to the measurements at 5-15 km distance from the salt surface, suggesting that the BrO formation time scale and effective life times during daytime are at least of the order of several minutes to a few hours. Additional in-situ ozone measurements indicate ozone depletion events linked to the episodes of high BrO abundance. This indicates that BrO is formed by bromine atoms reacting with ozone and then being recycled via BrO self-reaction and heterogeneous processes involving aerosol surfaces, as proposed for other environments (Polar Regions, volcanic plumes).

While we found high but steady HCHO levels, the observed NO₂ levels showed a distinct anti-correlation to BrO, indicating coupling of bromine- and NO_x-chemistry and thereby the influence of the pollution level of the ambient atmosphere. Formation of bromine nitrate probably delays the formation of large BrO amounts, but might also support the recycling of bromine atoms through heterogeneous chemistry.

How to cite: Kuhn, J., Kumar, V., Wagner, T., Warnach, S., and Platt, U.: Reactive bromine chemistry in the Rann of Kachchh salt desert, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3091, https://doi.org/10.5194/egusphere-egu2020-3091, 2020.

Volcanic eruptions emit halogen-containing species in varying quantities, with their emission ratio to tracer species such SO₂ varying between volcanoes, eruptions, and even phases of an eruptive event.

The bromine explosion is known to occur within volcanic plumes, converting bromine from HBr – the primary form in which it is emitted – to other forms, including the spectroscopically detectable BrO. Measurements of BrO have been made in the plumes of many volcanoes from both ground-based and satellite-based instruments. There also exist a small number of measurements of OClO.

We present results from WRF-Chem Volcano (WCV), a modified version of the three-dimensional regional atmospheric chemistry and transport model WRF-Chem and associated utilities. We have simulated the Christmas 2018 eruptive event of Mount Etna using a nested implementation the model at maximum lateral resolution of 1km, as well as a weaker emission plume representing Etna’s more common quiescent degassing state. The plume of this 2018 eruption was observed remotely by the TROPOMI instrument.

WCV is able to model the transport and dispersion of the plume. We compare these model outputs to the satellite observations and use this to estimate the volcanic emission column height.

In terms of chemistry, WCV is able to reproduce the bromine explosion and the major features of the satellite observation – including a cross-plume variation in the BrO/SO₂ column ratio. We find that variations in the BrO/SO₂ ratio are primarily caused by variations in the concentration of ozone. Ozone is consumed by bromine chemistry and is replenished by the mixing in of ozone-rich background air. This creates a zone of low ozone in the core of the plume which is consequently low in BrO and surrounded by a higher-ozone edge with a higher BrO/SO2 ratio.

For the temporal evolution of the plume, we find that the bromine-chemistry of a concentrated emission plume can be divided into four phases, also governed by ozone availability. In the last phase ozone limitation is minimal and the proportion of bromine in the form of BrO (and the BrO/SO2 ratio) is approximately stable. We find this stable regime also with a simulation of a weaker emission plume. These results could facilitate the use of remote-sensing BrO measurements as a means of quantifying total bromine emissions from volcanoes.

Oxidized forms of chlorine are modelled to be formed within the plume due to the heterogenous reaction of HOBr with HCl, forming BrCl that photolyzes and produces Cl radicals. We also investigate the extent to which mercury could be oxidized by halogens within the plume.

How to cite: Surl, L., Warnach, S., Wagner, T., Roberts, T., and Bekki, S.: Using WRF-Chem Volcano to model the in-plume halogen chemistry of Etna’s 2018 eruption, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10892, https://doi.org/10.5194/egusphere-egu2020-10892, 2020.

Reactive atmospheric halogens destroy tropospheric ozone (O₃), an air pollutant and greenhouse gas. The primary source of natural halogens is emissions from marine phytoplankton and algae, as well as abiotic sources from ocean and tropospheric chemistry, but how their fluxes will change under climate warming –and the resulting impacts on O₃– are not well known. Here we use an Earth system model to estimate that natural halogens deplete approximately 13 % of tropospheric O₃ in the present-day climate. Despite increased levels of natural halogens through the twenty-first century, this fraction remains stable due to compensation from hemispheric, regional, and vertical heterogeneity in tropospheric O₃loss. Notably, this halogen-driven O₃ buffering is projected to be greatest over polluted and populated regions, mainly due to iodine chemistry, with important implications for air quality.

How to cite: Iglesias-Suarez, F., Badia, A., Fernandez, R. P., Cuevas, C. A., Kinnison, D. E., Tilmes, S., Lamarque, J.-F., Long, M. C., Hossaini, R., and Saiz-Lopez, A.: Natural halogens buffer tropospheric ozone in a changing climate, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5355, https://doi.org/10.5194/egusphere-egu2020-5355, 2020.

Iodine chemistry plays an essential role in controlling the radiation budget by changing various atmospheric parameters. Iodine in the atmosphere is known to cause depletion of ozone via catalytic reaction cycles. It alters the atmospheric oxidation capacity, and lead to ultrafine particle formation that acts as potential cloud condensation nuclei. The ocean is the primary source of iodine; it enters the atmosphere through fluxes of gaseous reactive iodine species. At the ocean surface, seawater iodide reacts with tropospheric ozone (gas) to form inorganic iodine species in gaseous form. These species namely, hypoiodous acid (HOI) and molecular iodine (I₂) quickly photolyse to release reactive iodine (I) in the atmosphere. This process acts as a significant sink for tropospheric ozone contributing to ~16% ozone loss throughout the troposphere. Reactive iodine released in the atmosphere undergoes the formation of iodine monoxide (IO) or higher oxides of iodine (I_xO_x) via self-recombination reactions. It is known that inorganic iodine fluxes (HOI and I₂) contribute to 75% of the detected IO over the Atlantic Ocean. However, we did not observe this from ship-based MAX-DOAS studies between 2014-2017. At present, there are no direct observations of inorganic iodine (HOI; few for I₂) and are estimated via empirical methods derived from the interfacial kinetic model by Carpenter et al. in 2013. Based on the kinetic model, estimation of HOI and I₂ fluxes depends on three parameters, namely, ozone concentration, surface iodide concentration, and the wind speed. This parameterisation for inorganic fluxes assumes a sea surface temperature (SST) of 293 K and has limiting wind speed conditions. Since the parameterisation conditions assumed SST of 293 K higher uncertainties due to errors in activation energy creeps in the estimation of HOI flux compared to I₂ as the flux of HOI is ~20 times greater than that of I₂. For three consecutive expeditions in the Indian and Southern Ocean, we detected ~1 pptv of IO in the marine boundary layer. These levels are not explained by the calculated inorganic fluxes by using observed and predicted sea surface iodide concentrations. This method of iodine flux estimation is currently used in all global models, along with the MacDonald et al. 2014 iodide estimation method. Model output using these parameterisations have not been able to match the observed IO levels in the Indian and Southern Ocean region. This discrepancy suggests that the process of efflux of iodine to the atmosphere may not be fully understood, and the current parametrisation does not do justice to the observations. It also highlights that the flux of organic iodine may also play a role in observed IO levels, especially in the Indian Ocean region. A correlation of 0.7 was achieved above the 99% confidence limit for chlorophyll-a with observed IO concentration in this region. There is a need to carry more observations to improve the estimation technique of iodine sea-air flux thus improving model predictions of IO in the atmosphere.

How to cite: Inamdar, S., Tinel, L., Chance, R., Jane Carpenter, L., Prabhakaran, S., Chacko, R., Chandra Tripathy, S., Ulhas Kerkar, A., Kumar Sinha, A., Parli Venkateswaran, B., Sarkar, A., Roy, R., Sherwen, T., Alberto Cuevas, C., Saiz-Lopez, A., Ram, K., and Sharad Mahajan, A.: Iodine chemistry in the tropical and remote open ocean marine boundary layer, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-990, https://doi.org/10.5194/egusphere-egu2020-990, 2020.

Air pollution has been a hazard in China over recent decades threatening the health of half a billion people. Much effort has been devoted to mitigating air pollution in China leading to a tremendous reduction in primary pollutants emissions from 2013 to 2017, while a continuously worsening trend of surface ozone (O₃, a secondary pollutant and greenhouse gas) was observed over the same period. Atmospheric oxidation, dominated by daytime reactions involving hydroxyl radicals (OH), is the critical process to convert freshly-emitted compounds into secondary pollutants, and is underestimated in current models of China’s air pollution. Halogens (chlorine, bromine, and iodine) are known to profoundly influence oxidation chemistry in the marine environment; however, their impact on atmospheric oxidation and air pollution in China is unknown. In the present study, we report for the first time that halogens substantially enhance the total atmospheric oxidation capacity in polluted areas of China, typically 10% to 20% (up to 87% in winter) and mainly by significantly increasing OH level. The enhanced oxidation along the coast is driven by oceanic emissions of bromine and iodine, and that over the inland areas by anthropogenic emission of chlorine. The extent and seasonality of halogen impact are largely explained by the dynamics of Asian monsoon, location and intensity of halogen emissions, and O₃ formation regime. The omission of halogen emissions and chemistry may lead to significant errors in historical re-assessments and future projections of the evolution of atmospheric oxidation in polluted regions.

How to cite: Li, Q., Badia, A., Wang, T., Sarwar, G., Fu, X., Zhang, L., Zhang, Q., Fung, J., Cuevas, C. A., Wang, S., Zhou, B., and Saiz-Lopez, A.: Potential Effect of Halogens on Atmospheric Oxidation in China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3004, https://doi.org/10.5194/egusphere-egu2020-3004, 2020.

In the case of a hypothetical nuclear accident, fission products are released into the environment. Simulation tools are commonly used to predict the radiological consequences on populations. After the Fukushima accident, significant differences have been observed between measured and modeled concentrations for iodine 131. This can be attributed to the high reactivity of iodine in the atmosphere not considered in the current dispersion crisis tools.

To address this, a new gas-phase mechanism of atmospheric iodine chemistry was developed containing 248 reactions. In parallel, missing thermokinetic data were determined by molecular-scale simulations for iodous and iodic acids. The 0D simulation results showed a partial and rapid transformation of these iodinated gaseous compounds. The influence of several parameters (air quality, quantity and nature of iodine released) was evaluated. For all simulations, iodine is quickly found in the form of iodine oxides and nitroxides or gaseous iodinated organic compounds. The latter may be the cause of iodinated aerosols formation and deposition.

Results from the 3D chemistry-climate model CAM-Chem will be compared to iodine Fukushima deposits measurements. Implications for atmospheric chemistry (air quality and climate) will be discussed.

How to cite: Louis, F., Taamalli, S., Fèvre-Nollet, V., Li, Q., Cuevas, C. A., and Saiz-Lopez, A.: Atmospheric iodine chemistry from molecular level to 0D/3D simulations: applications to Fukushima nuclear accident, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3022, https://doi.org/10.5194/egusphere-egu2020-3022, 2020.

Ice is ubiquitous and one of the most important environmental reaction media on earth. Generally, chemical reactions take place slowly when temperature decreases according to Arrhenius Equation(k=A·e^-EA/RT). Recently, it has been found that several chemical processes are accelerated by freezing compared to those in aqueous phase. Reactive iodine species (I, I₂, IO, OIO, HOI) in atmosphere are related to ozone depletion event (ODE) and new particle formation (NPF) in polar troposphere, and finally affect climate change. It was reported that the high concentration of halogen compounds(IO, BrO) in austral spring in Antarctica but the exact mechanism and sources are not fully understood. The biological production of halogens are regarded as the major source of organic and I2. However, the (photo)chemical reactions to produce reactive iodine species are also regarded as possible mechanism to explain the high atmospheric iodine budget. In this presentation, I want to introduce enhanced chemical reaction with laboratory experimental results such as 1)accelerated oxidation of iodide(I^-) in ice to produce molecular iodine(I₂) and tri-iodide(I₃^-), 2)nitrite-induced activation of iodate(IO₃^-) into molecular iodine in frozen solution. The detailed experimental conditions and mechanism will be discussed in the presentation.

How to cite: Kim, K.: Redox chemical processes of iodine species with inorganic compounds in ice, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3179, https://doi.org/10.5194/egusphere-egu2020-3179, 2020.

How to cite: Cuevas, C. A., Corella, J. P., Maffezzoli, N., Vallelonga, P., Spolaor, A., Cozzi, G., Müller, J., Vinther, B., Barbante, C., Kjaer, H. A., Edwards, R., and Saiz-Lopez, A.: The history of Holocene atmospheric iodine over the North Atlantic, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3520, https://doi.org/10.5194/egusphere-egu2020-3520, 2020.

Ozone is an important atmospheric pollutant in the troposphere due to its high oxidation potential. In the Arctic troposphere, ozone mainly originates from transport and photo-chemical reactions involving nitrogen oxides and volatile organic compounds, resulting in a background mixing ratio of 30 to 50 nmol/mol. During polar spring, so-called tropospheric ozone depletion events (ODEs) are regularly observed, in which ozone mixing ratios in the boundary layer drop to almost zero levels coinciding with a surge in reactive bromine levels on the time scale of hours to days. The source of the reactive bromine is sea salt, i.e. aerosol and deposits on the ice. However, it is not fully understood how the salt bromide is oxidized and reactive bromine is released into the air. The most widely accepted emission mechanism is autocatalytic and termed “bromine explosion”. ODEs strongly change the lifetime of ozone and organic gases, they cause the removal and deposition of mercury as well as the transport of reactive bromine into the free troposphere. In order to model ODEs, the software package WRF-Chem is employed to simulate the meteorology and the emission, the transport, mixing, chemical reactions of trace gases as well as aerosols. For this purpose, the MOZART chemical reaction mechanism coupled with the MOSAIC aerosol model is extended to include bromine and chlorine chemistry. A resolution of 20 km for a 5,000 km x 5,000 km region in horizontal directions is employed, enabling the comparison of the simulation results to satellite GOME-2 BrO with a larger resolution. In vertical direction, 64 non-linear grid cells are used with a finer resolution near the ground. The simulation domain is centered north of Barrow (Utqiaġvik), Alaska and covers most of the Arctic region. The time from February 1 to May 1, 2009 is simulated. Improvements and differences to existing models include more complex bromine chemistry, the inclusion of chlorine chemistry, MOSAIC aerosols, and nudging of meteorological fields to ERA-INTERIM data.The simulations reveal that the first bromine explosions occur in early February in the Bering Sea and then extend to the Beaufort Sea in the middle of February, with further bromine explosions in the Arctic region through the end of the simulation. Simulations results are compared with the GOME-2 BrO measurements and in-situ ozone observations at Barrow (Utqiaġvik), Alaska. The comparison shows good agreement with respect to occurrence and location of ODEs. The simulations indicate that the existence and replenishment of bromine in the sea ice is necessary for the ODEs to occur throughout the observation time. Inclusion of direct release of bromine by the deposition of ozone is essential for the proper prediction of the frequent recurrence of ODEs as found through observations. The largest uncertainty in the model is the strength of the bromine deposition and emission from the ice/snow surface as well as the amount of available bromine in the sea salt, which is varied in a parameter study.

How to cite: Herrmann, M., Sihler, H., Platt, U., and Gutheil, E.: Tropospheric Ozone Depletion Events in the Arctic Spring of 2009: Modeling and Observations , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5035, https://doi.org/10.5194/egusphere-egu2020-5035, 2020.

Oceans are the general emitter of dimethyl sulfide (DMS), the major natural sulfur source, and halides and cover approximately 70 % of Earth’s surface. The main DMS oxidation products are SO₂, H₂SO₄ and methyl sulfonic acid (MSA). Hence, DMS is very important for formation of non-sea salt sulfate (nss‑SO₄^2-) aerosols and secondary particulate matter and thus global climate. Reactive halogen compounds, activated by multiphase chemistry processes, are known to effectively deplete ozone, oxidise VOCs (especially DMS under marine conditions) and remove NOx from the atmosphere by conversion into particulate nitrate. Despite many previous model studies, a detailed representation of the multiphase chemistry occurring in aqueous aerosols and cloud droplets in CTMs is still missing.

To develop a detailed representation, a manual reduction of near-explicit multiphase chemistry mechanisms by means of detailed box model studies has been performed. The mechanism has been developed from the near-explicit DMS and halogen multiphase chemistry mechanism, CAPRAM DM1.0 and CAPRAM HM3. The reduced mechanism is evaluated by process model studies. Comparisons of simulations performed with the explicit and reduced mechanism reveals that the deviations are below 5 % for key inorganic and organic air pollutants and oxidants under pristine ocean and polluted coastal conditions, respectively.

Subsequently, the reduced mechanism has been implemented into the chemical transport model COSMO-MUSCAT and tested by 2D-simulations. Simulations are performed for two different meteorological scenarios mimicking unstable and stable weather conditions over the pristine ocean. The simulations demonstrate that the modelled concentrations of important halogen compounds such as HCl and BrO agree with ambient measurements demonstrating the applicability of the mechanism for tropospheric modelling investigations.

The 2D studies with the reduced mechanism are carried out to examine the oxidation pathways of DMS in a cloudy marine atmosphere in detail. They have shown that clouds have both a direct and an indirect photochemical effect on the multiphase processing of DMS and its oxidation products. The direct photochemical effect is related to in-cloud chemistry that leads to high DMSO oxidation rates and subsequently an enhanced formation of methane sulfonic acid compared to aerosol chemistry. The indirect photochemical effect is characterised by cloud shading, particularly in the case of stratiform clouds. The lower photolysis rates below the clouds affects strongly the activation of Br atoms and lowers the formation of BrO radicals. The corresponding DMS oxidation flux is particularly lowered under thick optical clouds. Besides, high updraft velocities lead to a strong vertical mixing of DMS into the free troposphere predominately under convective conditions. Furthermore, clouds reduce the photolysis of hypohalogeneous acids (HOX, X=Cl, Br, I) resulting in higher HOX-driven sulfite oxidation rates in aqueous aerosol particles below clouds.

How to cite: Hoffmann, E. H., Tilgner, A., Schrödner, R., Wolke, R., and Herrmann, H.: Towards an operational CAPRAM multiphase halogen and DMS chemistry treatment in the chemistry transport model COSMO-MUSCAT, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8752, https://doi.org/10.5194/egusphere-egu2020-8752, 2020.

How to cite: Yuanyuan, L.: Photoinduced Production of Chlorine Molecules from Titanium Dioxide Surfaces Containing Chloride, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8841, https://doi.org/10.5194/egusphere-egu2020-8841, 2020.

Bromine explosions and corresponding ozone depletion events (ODEs) are common in the Arctic spring. The snowpack on sea ice and sea salt aerosols (SSA) are both thought to release bromine, but the relative contribution of each source is not yet known. Furthermore, the role of atmospheric conditions is not fully understood. Long-term measurements of bromine monoxide (BrO) provide useful insight into the underlying processes of bromine activation. Here we present a four-year dataset (2016-2019) of springtime BrO partial columns retrieved from Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements in Eureka, Canada (80.1° N, 86.4° W). Due to the altitude of the measurement site (610 m), the measurements often represent BrO above the shallow boundary layer, and the strength of the temperature inversion has limited impact on the BrO partial columns. When the boundary layer is deep, however, the effects of the enhanced vertical mixing manifest as an increase in the minimum BrO values (and reduced ODE frequency) for wind speeds of ~8 m/s or greater. We find that BrO events show two modes differentiated by local wind direction and air mass history. Longer time spent in first-year sea ice areas corresponds to increased BrO for one of these modes only. We argue that snow on multi-year ice (salted and acidified by Arctic haze) might also contribute to bromine release. The MAX-DOAS measurements show that high aerosol optical depth is required to maintain lofted BrO. In situ measurements indicate that accumulation mode aerosols (mostly Arctic haze) have no direct correlation with BrO. The presence of coarse mode aerosols, however, is a necessary and sufficient condition for observing enhanced BrO at Eureka. The measurements of coarse mode aerosols are consistent with SSA generated from blowing snow. The good correlation between BrO and coarse mode aerosols (R² up to 0.57) supports the view that SSA is a direct source of bromine to the polar troposphere.

How to cite: Bognar, K., Zhao, X., Strong, K., Chang, R. Y.-W., Frieß, U., Hayes, P. L., McClure-Begley, A., Morris, S., Tremblay, S., and Vicente-Luis, A.: Measurements of bromine monoxide over four halogen activation seasons in the Canadian high Arctic, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8996, https://doi.org/10.5194/egusphere-egu2020-8996, 2020.

Iodine-131, when released into the environment during severe nuclear power plant accident can have a high radiological impact on the population at short term [1]. Interaction between gaseous Iodine compounds and aerosols was not considered by the current post-accident management. In this context, this work was focused on investigating the influence of sea salt aerosols on the transport of gaseous methyl iodide (CH₃I). The identification of uptake processes as well as the formation of new products at the particle surfaces was the main objectives.

We have studied the interaction between NaCl particles as surrogate of sea salt particles and CH₃I in various humidity conditions to reproduce the atmospheric conditions.

The nature of this interaction was investigated by Infrared Spectroscopy (DRIFTS, Diffuse Reflectance Infrared Fourier Spectroscopy). Solid NaCl was exposed to CH₃I (1000 and 500 ppm) with a relative humidity (RH) ranging between 0 and 80%.

DRIFTS results clearly evidenced adsorbed CH₃I on NaCl particles surface under both dry and humid conditions. The adsorption process can be fitted with First-order Langmuir adsorption isotherm model and exhibited very low uptake coefficients in all the experimental conditions.

Additionally, to the CH₃I absorption bands, the DRIFT spectrum evidenced typical absorption bands that could be assigned either to the CH₂ deformation of CH₂I₂ or to CH₃ degenerate rocking of CH₃Cl. The formation of new bands appears only when CH₃I is in presence of halogenated salts. However, at RH = 80%, the water layer at the particle surface inhibits the interaction between gaseous CH₃I and NaCl surface due to the low solubility of CH₃I in water.

Theoretical calculations are carried out to complement the experimental results. Isolated hydrated clusters of CH₃I are characterized by means of electronic structure calculations and ab initio molecular dynamics is used to mimic the CH₃I / salt system at various humidities.

Although the uptake and accommodation coefficients of CH₃I are quite low, a coverage of particle surface with CH₃I-derived compounds may affect the reactivity of the particles and in term the cycling life of Iodine in the atmosphere.

Reference

[1] Lebel, L. S.; Dickson, R. S.; Glowa, G. A. J. Environ. Radioact. 2016, 151, 82–93.

We acknowledge support by the French government through the Program “Investissement d'avenir” through the Labex CaPPA (contract ANR-11-LABX-0005-01) and I-SITE ULNE project OVERSEE (contract ANR-16-IDEX-0004), CPER CLIMIBIO (European Regional Development Fund, Hauts de France council, French Ministry of Higher Education and Research) and French national supercomputing facilities (grants DARI x2016081859 and A0050801859).

How to cite: Toubin, C., Houjeij, H., Infuso, M., Anne-Cécile, G., Gwenaelle, L. B., Laurent, C., Sonia, T., Florent, L., Denis, D., and Sophie, S.: Experimental and theoretical study on the capture/desorption of gaseous methyl iodide on sea salt aerosols, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11132, https://doi.org/10.5194/egusphere-egu2020-11132, 2020.

ClNO₂ and Cl₂ can affect atmospheric oxidation and thereby the formation of ozone and secondary aerosols, yet their sources and production mechanisms are not well understood or quantified. In this study we present field observations of ClNO₂ and Cl₂ at a suburban site in eastern China during April 2018. Persistent high levels of ClNO₂ (maximum ~3.7 ppbv; 1 min average) were frequently observed at night, due to the high ClNO₂ yield (φ(ClNO₂), 0.56 ± 0.20) inferred from the measurements. The φ(ClNO₂) value showed a positive correlation with the [Cl^-]/[H₂O] ratio, and its parameterization was improved by the incorporation of [Cl^-]/[H₂O] and the suppression effect of aerosol organics. ClNO₂ and Cl₂ showed a significant correlation on most nights. We show that the Cl₂ at our site was likely a co-product with ClNO₂ from N₂O₅ uptake on aerosols that contain acidic chloride, rather than being produced by ClNO₂ uptake, as previously suggested. The Cl₂ yield (φ(Cl₂)) derived from the N₂O₅ uptake hypothesis exhibited significant correlations with [Cl^-] and [H⁺], based on which a parameterization of φ(Cl₂) was developed. The derived parameterizations of φ(ClNO₂) and φ(Cl₂) can be used in models to quantify the nighttime production of ClNO₂ and Cl₂ and their impact on the next day’s photochemistry.

How to cite: Xia, M., Wang, T., Peng, X., Wang, W., Yu, C., Sun, P., Li, Y., Liu, Y., Xu, Z., Wang, Z., Xu, Z., Nie, W., and Ding, A.: Significant production of ClNO2 and possible source of Cl2 from N2O5 uptake at a suburban site in eastern China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12946, https://doi.org/10.5194/egusphere-egu2020-12946, 2020.

Nitryl chloride (ClNO₂) plays an important role as a night-time reservoir of NO_X and the source of Cl radical during the daytime, which consequently affects the ozone photochemistry. Its impacts on regional air quality in East Asia, however, are not fully understood so far. We here use extensive observations during the international KORea-US cooperative Air Quality field study in Korea (KORUS-AQ), which occurred in May-June 2016, with a 3-D chemistry transport model to examine the impacts of ClNO₂ chemistry on radical species and total nitrate concentrations in East Asia. We first update the model by implementing chlorine chemistry and latest anthropogenic chlorine emissions of China and South Korea. We conduct model simulations for May-June, 2016 and validate the model by comparing against the observations from the KORUS-AQ campaign. We find that the ClNO₂ chemistry in the model results in an increase of ozone by ~1.4 ppbv (~2.5%), Cl radical by ~ 4.6x10³ molec cm^-3 (~3600%), OH ~8.2x10⁴ molec cm^-3 (~5.3%), HO₂ ~6.6 molec cm^-3 (~3.0%), a decrease of TNO₃ (HNO₃ + nitrate aerosol) concentrations by ~2 μg m^-3 on a daily mean basis during the campaign. Overall, the enhanced conversion of NO to NO₂ driven by ClNO₂ chemistry contributes to higher oxidant concentrations in the model. As a result, the updated model shows a better agreement with the observations in Korea during the KORUS-AQ campaign.

How to cite: Kim, H., Park, R., Jeong, J., Kim, S., Jeong, D., Fu, X., and Cho, S.: Effect of nitryl chloride chemistry on oxidants concentrations during the KORUS-AQ campaign, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13602, https://doi.org/10.5194/egusphere-egu2020-13602, 2020.

The oxidative capacity, usually represented by the concentration of OH radicals in the troposphere, regulates the lifetime of reactive compounds injected into the atmosphere by the biosphere and by anthropogenic activities. Recently, naturally emitted halogenated species (I, Br, Cl) have been showed to play a significant role in the consumption of global tropospheric ozone, a primary precursor of the hydroxyl radical. So far, the state-of-the-art chemistry of iodine, bromine, and chlorine has been implemented in a few global chemistry-transport models (GEOS-CHEM, CAM-Chem, TOMCAT, WRF-Chem). The 3D global chemistry-climate model (LMDz-INCA) has been recently updated to consider the chemistry of halogens. We present here the impact of this chemistry on the global oxidant budgets as well as the lifetime of chemically active species. We discuss how this chemistry affects the self-regulation of radicals in present low-polluted atmospheres as well as pre-industrial and future climate scenarios.

How to cite: Karam, C. and Szopa, S.: The role of halogens in the regulation of the oxidative capacity of the Earth’s troposphere in low-polluted environments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15450, https://doi.org/10.5194/egusphere-egu2020-15450, 2020.

Atmospheric halogens chemistry like the catalytic reaction of bromine and chlorine radicals with ozone (O₃) has been known to cause the springtime surface-ozone destruction in the polar region. Although the initial atmospheric reactions of chlorine with ozone are well understood, the final oxidation steps leading to the formation of chlorate (ClO₃^-) and perchlorate (ClO₄^-) remain unclear due to the lack of direct evidence of their presence and fate in the atmosphere. In this study, we present the first high-resolution ambient data set of gas-phase HClO₃ (chloric acid) and HClO₄ (perchlorate acid) obtained from the field measurement at the Villum Research Station, Station Nord, in high arctic North Greenland (81°36’ N, 16°40’ W) during the spring of 2015. A state-of-the-art chemical ionization atmospheric pressure interface time-of-flight mass spectrometer (CI-APi-TOF) was used in negative ion mode with nitrate ion as the reagent ion to detect the gas-phase HClO₃ and HClO₄. We measured significant level of HClO₃ and HClO₄ only during the springtime ozone depletion events in the Greenland, with concentration up to 9x10⁵ molecule cm^-3. Air mass trajectory analysis shows that the air during the ozone depletion event was confined to near-surface, indicating that the O₃ and surface of sea-ice/snowpack may play important roles in the formation of HClO₃ and HClO₄. We used high-level quantum-chemical methods to calculate the ultraviolet-visible absorption spectra and cross-section of HClO₃ and HClO₄ in the gas-phase to assess their fates in the atmosphere. Overall, our results reveal the presence of HClO₃ and HClO₄ during ozone depletion events, which could affect the chlorine chemistry in the Arctic atmosphere.

How to cite: Tham, Y. J., Sarnela, N., Cuevas, C. A., Siddharth, I., Beck, L., Saiz-Lopez, A., and Sipilä, M.: Observation of HClO3 and HClO4 in the Arctic atmosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16908, https://doi.org/10.5194/egusphere-egu2020-16908, 2020.

Arctic Amplification, the rapid increase of air temperature in higher latitudes over the last decades, is expected to have drastic impacts on all the sub-systems of the Arctic ecosystem. Bromine Oxides play a key role in the atmospheric composition of the Arctic. During polar spring, bromine molecules are released from young sea ice covered regions.  A rapid chemical chain reaction starts, the -so called 'bromine explosion', which depletes ozone, alters the production of OH, and thereby eventually changes the oxidizing capacity of the troposphere. Halogens oxidize elemental to gaseous mercury, which may then be deposited and harm the ecosystem. Based on current literature, there is considerable uncertainty on the impact of Arctic Amplification on halogen evolution. On one hand, the melting of multi-year sea ice should result in formation of more young sea ice, which favors bromine release. On the other hand, BrO explosion events are triggered by low temperatures, an effect expected to be reduced due to Arctic Amplification. Moreover, changes of other meteorological drivers, such as cyclone frequency and wind speed may impact on BrO amounts in the Arctic troposphere.

In this study, a long-term time-series of tropospheric BrO derived from 4 UV-VIS instruments (GOME, SCIAMACHY, GOME-2A, GOME-2B) is used as a basis, in order to investigate the impact of Arctic Amplification on BrO amounts in the Arctic. The long-term BrO data is being compared to sea ice age (NSIDC) and meteorological (air temperature, mean sea level pressure, wind speed and boundary layer height from ERA-5 & ASR-2) data. Our results focus on determining the relation between tropospheric BrO and its drivers, and especially on how the drivers impact on the formation of BrO plumes. Different cases studies throughout the 22 years of the BrO dataset were performed and evaluated. The changes in the tropospheric BrO abundances come in general agreement with changes in the drivers of BrO explosion events.

We gratefully acknowledge the funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Projektnummer 268020496 – TRR 172, within the Transregional Collaborative Research Center “ArctiC Amplification: Climate Relevant Atmospheric and SurfaCe Processes, and Feedback Mechanisms (AC)³”.

How to cite: Bougoudis, I., Blechschmidt, A.-M., Richter, A., Seo, S., and Burrows, J.: Investigating the Relation of Arctic Tropospheric Bro Derived by Satellite Remote Sensing to Sea Ice Age and Meteorological Driving Mechanisms Under the Impact of Arctic Amplification, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16914, https://doi.org/10.5194/egusphere-egu2020-16914, 2020.

Chlorinated Very Short-Lived Substances (Cl-VSLS) are now recognised as a significant source of inorganic chlorine in both the troposphere and stratosphere (e.g. Hossaini et al., 2016, 2019). The most abundant Cl-VSLS are dichloromethane (CH2Cl2), chloroform (CHCl3), perchloroethylene (C2Cl4) and 1,2−dichloroethane (C2H4Cl2), all of which have significant – but poorly constrained – industrial sources. Global surface observations have shown that the tropospheric abundance of CH2Cl2 and CHCl3 has increased significantly in recent years. For instance, the global surface abundance of CH2Cl2 has more than doubled since the early 2000s and in 2018 was ~42 ppt. Despite this, there has been no recent attempt to create a consistent set of gridded Cl-VSLS emissions with which global models can use to study their impacts. Here, we describe and evaluate a new set of gridded time-varying global emissions of CH2Cl2, CHCl3, C2Cl4 and C2H4Cl2, informed by novel bottom-up industrial emission data. The performance of the emission inventories in the TOMCAT chemical transport model are assessed using data from both long-term surface monitoring networks and a range of tropospheric aircraft campaigns. We use the model to quantify regional variability in Cl-VSLS throughout the troposphere and outline further plans for a new model intercomparison effort to examine the impacts of VSLS in the troposphere and stratosphere.

How to cite: Hossaini, R., Bednarz, E., and Chipperfield, M.: Chlorinated Very Short-Lived Substances: development + evaluation of gridded emissions for global models and on recent emission trends, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20311, https://doi.org/10.5194/egusphere-egu2020-20311, 2020.