The retention coefficients for halogen gases upon freezing of water are currently not estimated. Estimating their retention coefficients is an important metric, enabling atmospheric chemists and modelers to better approximate the respective influences and lifetimes of trace gasses in the atmosphere. Using molecular dynamic simulations that simulate the freezing of cloud water droplets containing halogen gasses in the upper troposphere (220°K), we have revealed that Cl₂, Br₂, and I₂ are entirely retained when water droplets are frozen during deep convection. The results of the simulations show that the presence of halogen gasses in cloud droplets retards their freezing rates by approximately 35% to 62%.  Enumeration of hydrogen and halogen bonds formed between gas species and water in cloud droplets shows that substantially more halogen bonding than hydrogen bonding occurs among halogen gasses. Additionally, data indicates the size of halogen species within cloud droplets may affect their freezing rates. Our results provide a theoretical framework to make the first estimates regarding halogen gas retention coefficients, helping to elucidate impacts halogens may have on the gas transportation dynamics and chemistries of the upper troposphere and lower stratosphere (UTLS). As halogen gas emissions continue to increase globally, this study calls upon the emergent need to assess the role of halogen gasses in UTLS chemistry, especially in the deep convective regions.

How to cite: Yerby, C. J., Bertho, G. G., Zhu, C., and Francisco, J. S.: Molecular Dynamics Studies of Halogen Bonding on the Freezing in Clouds, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8392, https://doi.org/10.5194/egusphere-egu23-8392, 2023.

Besides H₂O, CO₂ and sulphur, halogens (F, Cl, Br, I) are important volatile components in magmas. The extremely high chemical activity of halogens in melts and liquids leads to a significant influence on (a) magmatic properties, (b) the degassing of magma, (c) the extraction, transport and deposition of metals, (d) the chemistry of volcanic emissions and (e) the composition of the atmosphere. Indeed, their geochemical behaviour can be used as a key indicator of the genetic conditions and evolution of magma.

In July 2021 a joint interdisciplinary campaign of petrologists, chemists and atmospheric physicists took place at Mt Etna volcano, Italy. Due to the favourable volcanic activity at Mt Etna (frequent paroxystic activity characterized by lava fountaining) we were able to collect  a unique dataset of simultaneously sampled fresh tephra fallout, in-situ gas samples (multiGAS, alkaline traps, 1,3,5-Trimethoxybenzene impregnated denuders) and spectral data with remote sensing techniques (DOAS, FTS, IFPICS) of the volcanic plume. The halogen and sulphur content was analysed in the volcanic plume as well as in the melt inclusion and glasses of the deposits. Results of the various applied techniques are presented. They allow us a direct comparison of degassing signatures (e.g., Cl/F, Br/Cl, and S/Cl) from the pre-eruptive melt to the volcanic plume.

How to cite: Bobrowski, N., Beikert, J., Botcharnikov, R., Buhre, S., Butz, A., Fuchs, C., Geil, B., Giuffrida, G. B., Heimann, J., Helo, C., Hoffmann, T., Knapp, M., Krasheninnikov, S., Kuhn, J., Liuzzo, M., Ludwig, T., Nies, A., Schmitt, A., and Sturm, A.: Halogens as tracers for magma evolution from the mantle source to the atmosphere – insights from simultaneous probing of tephra fallout and gas phase in the volcanic plume, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9539, https://doi.org/10.5194/egusphere-egu23-9539, 2023.

The ozone-depleting substances chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs) and their major substitutes hydrofluorocarbons (HFCs) are all potent greenhouse gases, and their atmospheric concentrations and emission sources have received international attention. The relevant studies have been carried out at multiple background sites around the world, but there is no report on the southern slope of the Himalayas. For the first time, this study set up the Medog background observation site 30 km away from Medog County on the southern slope of the Himalayas (95.5262ºE, 29.5314ºN, 1298.8 m above sea level) in China. From August 10 to September 19 and November 3 to November 30 in 2021, 114 atmospheric samples were collected instantaneously using evacuated electro-polished stainless-steel canisters and manual pressurization equipment and 1-3 samples were collected per day. Nine substances (CFC-11, 12, 113; HCFC-22, 141b, 142b; HFC-23, 125, 134a) were analyzed using a high-precision measurement system of halogenated gases (ODS5-pro). For each substance, all the atmospheric samples were divided into two categories: background samples and polluted samples. The background samples are those whose concentrations were within the range of the background concentrations (measured at the Ragged Point site at the same latitude in 2021) ± 3σ (instrument precision), and the others were classified as polluted samples. Our results showed that the number of the polluted samples of each substance accounted for about 40%-90%. In addition, we found that the mixing ratios of CFC-113, HFC-23, and HCFC-22 in the polluted samples were 93, 44 and 311 pptv, respectively, with higher mixing ratios (31.6%, 24.5%, and 22.5%) above the background levels than other substances (4.3%~10.2%). Furthermore, CFC-113 and HFC-23 were significantly correlated (R = 0.429, P < 0.01), suggesting that they may have similar sources. Both Backward Trajectory and Potential Source Contribution Function of the polluted samples of CFC-113, HFC-23, and HCFC-22 found that the polluted air masses mainly came from the northeast of India and other regions southwest of the sampling site. In contrast, the background air masses mainly came from the local areas. The concentrations of CFC-113, HFC-23, and HCFC-22 in the polluted samples observed in this study, likely from the northeast of India, were about 20-30% higher than the results of aircraft samples conducted by Say et al. (2019) over Northern and Southern India in 2016. In the future, we will continue to carry out atmospheric observations at the Medog background site and try to use the suitable atmospheric transport model to inverse the emissions in the surrounding areas.

How to cite: Wu, J., Liu, Z., Yao, B., An, M., Niu, Y., Zhao, W., Yu, H., Wang, T., Dong, B., and Peng, L.: Atmospheric observation and source analysis of CFCs, HCFCs and HFCs at the Medog background site on the southern slope of the Himalayas, China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10599, https://doi.org/10.5194/egusphere-egu23-10599, 2023.

Halocarbons have been recognized for their role as major ozone-depleting substances (ODSs) since the 1970s, and some also function as greenhouse gases (GHGs). International agreements, such as the Montreal Protocol, Kyoto Protocol, and Paris Agreement, were established for worldwide cooperation to gradually reduce the production and use of halocarbons. Initial success was achieved in phasing out global chlorofluorocarbon (CFC) production, but recent studies found an unexpected decrease in the rate of decline in the atmospheric concentration of trichlorofluoromethane (CFC-11) after 2012.

Historically, halocarbons have been emitted from various anthropogenic sources (e.g., the dry cleaning industry, electronic industry, and refrigeration) in Hong Kong. Emission sources in the Pearl River Delta (PRD) region, such as chemical manufacturing, also have remarkable impacts on the ambient halocarbons in Hong Kong. The ambient mixing ratios of major CFCs were declining in Hong Kong and the PRD region before 2010. However, no continuous measurements of ambient halocarbons were conducted in Hong Kong after 2010. Given that CFC emissions from the PRD region account for up to 25% of their total emissions in China, any unexpected CFC emissions in recent years will have significant impacts on the atmospheric abundance of halocarbons worldwide.

We have been continuously monitoring ambient halocarbons in Hong Kong since Fall 2020. The temporal variability of major halocarbons and their source origins have been extensively investigated using multiple approaches. Our results indicate lower enhancements beyond the background values for major regulated CFCs and CCl₄ than later controlled HCFCs and HFCs, suggesting the greater progress of Montreal Protocol implementation for the former species. The notable high enhancement values of non-regulated halocarbons from the north direction indicate their widespread usage in China. This work provides insight into the progress made in implementing the Montreal Protocol in Hong Kong and the surrounding region and the importance of continuous emission control.

How to cite: Gu, D., Cao, X., and Leung, K. F.: Study of ambient halocarbons in Hong Kong: temporal variability and implication on source origins, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16987, https://doi.org/10.5194/egusphere-egu23-16987, 2023.

The chlorine (Cl·) and bromine atom (Br·) are known to destroy ozone, and Br· accelerates the deposition of toxic mercury (Hg). However, their abundances, sources and impacts in polluted regions are not well understood. In this talk, we give an overview of recent measurements of significant levels of Cl₂ and Br₂— a producer of Cl· and Br·, respectively —in the coastal atmosphere of Hong Kong. We present field and laboratory evidence to show photodissociation of particulate nitrate being a major production pathway for daytime Cl₂ and Br₂ and reactive uptake of N₂O₅ on aerosols as an important nighttime source. Model-calculated and Cl· and Br· from these di-halogens have significant impacts on VOC oxidation, OH radical, ozone production, and Hg oxidation. The findings suggest that reactive halogens may play a larger role in the atmospheric chemistry and air quality of polluted coastal regions than previously thought and call for more research on this issue.

How to cite: Wang, T. and the study team: Pollution-derived Cl2 and Br2 boost oxidation power of the coastal atmosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11587, https://doi.org/10.5194/egusphere-egu23-11587, 2023.

Short-lived bromo-, chloro- and iodocarbons from marine and anthropogenic sources contribute to the atmospheric halogen budgets and to ozone depletion in the troposphere and stratosphere. Their spatial variations are poorly known, given the sparse observations of marine and atmospheric concentrations. The distribution and air-sea fluxes of halocarbons need to be quantified in order to clarify the oceanic contributions to future tropospheric and stratospheric ozone chemistry.

Here we present the first marine and atmospheric halocarbon dataset from the research cruise SO287-CONNECT (Pan-Atlantic connectivity of marine biogeochemical and ecological processes and the impact of anthropogenic pressures). The transit of RV SONNE from Las Palmas, Spain (departure: 11.12.2021) to Guayaquil, Ecuador (arrival: 11.01.2022) was conducted to decipher the coupling of biogeochemical and ecological processes and their influence on atmospheric chemistry along the transport pathway of water from the upwelling zones off Africa into the Sargasso Sea and further to the Caribbean and the equatorial Pacific. A comprehensive work program, which combined continuous underway and station work, marine and atmospheric measurements and sampling with incubation experiments was conducted.

The distribution of short-lived halocarbons, e.g. bromoform (CHBr₃), dibromomethane (CH₂Br₂), methyl iodide (CH₃I), and trichloromethane (CHCl₃) was highly dynamic in both ocean and atmosphere. We calculate the air-sea exchange of the compounds and relate physical and biological parameters to our observations. Among these are transport processes (e.g. long-range transport, eddies) and we show the varying composition of air and water masses and the potential sources of the compounds. For the first time, we estimate the contribution of the floating macroalgae Sargassum to halocarbon cycling around the North Atlantic gyre and in the Caribbean. The evaluation of the comprehensive data set collected during SO287-CONNECT improves our knowledge on the general role of the great Atlantic Sargassum belt and anthropogenic pollution in elemental biogeochemical cycles, as well as on trace gas exchange across the ocean-atmosphere interface.

How to cite: Quack, B., Booge, D., Hepach, H., Atlas, E., Karnatz, J., Rosa, A., Cardoso, C., Ball, S., Potin, P., and Röttgers, R.: Halocarbon dynamics from Las Palmas to Guayaquil in winter 2021/2022 – Results of SO287-CONNECT, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6381, https://doi.org/10.5194/egusphere-egu23-6381, 2023.

Ozone Depletion Events (ODEs) have been observed since the late 1990s in the polar regions during spring, often in combination with Bromine Explosion Events (BEEs). In a heterogeneous, autocatalytic, chemical chain reaction cycle, inorganic bromine is released from the cryosphere into the troposphere and depletes ozone, sometimes to below detection limit. Besides low temperatures favoring the bromine explosion reactions, two different meteorological conditions are mainly observed during 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. The second condition often occurs in combination with polar cyclones, where bromine can be recycled aloft on snow and aerosol surfaces.

In this study, two long term ozone data sets, one from ozone sondes launched in Ny-Ålesund and the other from in-situ measurements on Zeppelin mountain – located close to Ny-Ålesund – have been evaluated from March until May between 2010 and 2021 to detect ODEs. To analyze the prevailing weather conditions during these events, ERA5 reanalysis data has been used and separated between weather conditions during ODEs and no-ODEs based on the respective ozone data set. The evaluation of the two data sets led to very consistent results: during ODEs, lower pressure is observed east of Svalbard and higher pressure over Greenland, leading to a transport of cold polar air from the north to Ny-Ålesund. Also higher wind speed and a higher boundary layer are noticed, supporting the assumption, that ODEs often occur in combination with polar cyclones.

Using the same approach, the long-term tropospheric BrO data set from Bougoudis et al., 2020 in combination with S5P TROPOMI retrievals of tropospheric BrO has been used to analyze BrO patterns. During ODEs in Ny-Ålesund, the satellite data show elevated values all over the Arctic, but especially north of Svalbard.

This work was supported by the DFG funded Transregio-project TR 172 “Arctic Amplification (AC)³“ in subproject C03.

How to cite: Zilker, B., Richter, A., Blechschmidt, A.-M., Bougoudis, I., Seo, S., von der Gathen, P., Bösch, T., and Burrows, J. P.: Investigation of weather conditions and BrO during ozone depletion events between 2010 and 2021 in Ny-Ålesund, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11859, https://doi.org/10.5194/egusphere-egu23-11859, 2023.

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 destruction of boundary layer ozone during polar springs. These recurrent episodes of catalytic ozone depletion, better known as “ozone depletion events” (ODEs) are driven by enhanced concentrations of reactive bromine compounds. The proposed mechanism by which these compounds are released into the troposphere is known as “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 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 spatio-temporal 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). One advantage of our retrieval is its independence from any external input data, thereby avoiding systematic biases from external datasets. We used a modified k-means clustering and methods from statistical data analysis to separate tropospheric and stratospheric partial columns, 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 high spatial resolution as the TROPOMI instrument, because no model data with coarse resolution is used. In a second step, the retrieved tropospheric slant column densities (SCDs) are converted to vertical column densities (VCDs).

TROPOMI’s improved spatial resolution is then utilized to study the spatial extent and shape of BrO plumes detected in the Arctic region. For this, a combination of morphological filters and connected component labeling is used to provide a statistical overview of all enhanced BrO plumes detected above certain sensitivity thresholds in the Arctic spring of 2019. This provides a lower limit for the spatial extent of enhanced BrO events (and hence also for ODEs) of around 40-60 km. Additionally, seasonal trends in size and shape of the BrO plumes as well as correlations to relevant meteorological parameters are investigated.

How to cite: Schöne, M., Sihler, H., Warnach, S., Borger, C., Herrmann, M., Gutheil, E., Beirle, S., Platt, U., and Wagner, T.: Tropospheric BrO in Arctic Spring 2019 measured by S5-P/TROPOMI - A statistical analysis of the spatial expansion and shape of tropospheric BrO plumes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11887, https://doi.org/10.5194/egusphere-egu23-11887, 2023.

While the importance of bromine chemistry for the Arctic surface ozone budget is well documented, the effect of iodine chemistry has received less attention. Here we present observations performed as part of the ship-based Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, where halogen oxides were measured during the sunlit period from March to October 2020. Ozone shows drastic loss during the boreal spring (March, April and May), when near-complete depletion is regularly observed, highlighting that ozone depletion in the central Arctic is widespread. The drastic ozone depletion coincides with ‘bromine explosion’ episodes, when bromine oxide (BrO) reaches values as high as 14.8±0.8pptv. In contrast, observations of IO show the presence of active iodine chemistry on most days during the whole sunlit period (including boreal spring, summer and autumn), presenting elevated levels of IO (usually between 0.2 and 1 pptv) that peak during spring (2.9±0.3 pptv). We find that chemical reactions between iodine and ozone are the second highest contributor to ozone loss over the study period, after ozone photolysis-initiated loss and ahead of bromine.

How to cite: Cuevas, C. A., Benavent, N., Mahajan, A. S., Li, Q., Schmale, J., Angot , H., Jokinen, T., Quéléver, L. L. J., Blechschmidt, A.-M., Zilker, B., Richter, A., Serna, J. A., Garcia-Nieto, D., Fernandez, R. P., Skov, H., Dumitrascu, A., Simões Pereira, P., Abrahamsson, K., Bucci, S., and Duetsch , M. and the MOSAiC iodine Team: Substantial contribution of iodine to Arctic ozone destruction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15972, https://doi.org/10.5194/egusphere-egu23-15972, 2023.

Nitryl chloride (ClNO₂) has been reported as a critical species of chlorine chemistry. Its chemistry interrupts a nighttime sink of NO_X and emits chlorine radical (Cl•) in the daytime, consequently altering gaseous and aerosol chemistry. Recent field studies have also measured considerable concentrations of ClNO₂ in South Korea under the influences of natural and anthropogenic chlorine sources. However, the impacts of ClNO₂ chemistry on air quality in South Korea have yet to be evaluated. We validate simulated ClNO₂ and its chemistry in South Korea using observations and a 3-D chemical transport model (CTM) during the Korea-United States Air Quality field study. We implemented the latest Chinese and Korean anthropogenic chlorine emissions in the model. We found that the model reproduces the observed spatial and temporal variations of ClNO₂, including its local and transboundary transport and precursors. We found that ClNO₂ chemistry results in a more efficient conversion of NO to NO₂ at night and daytime acceleration of the NO_X-O₃ cycle. It results in an increase of O₃ (1.1%), NO_X (3.1%), OH (2.0%), HO₂ (0.8%), and Cl• (507.8%) and a decrease of TNO₃(HNO₃ + aerosol nitrate, 1.7%) on the campaign mean basis.

How to cite: Kim, H., Park, R., Jeong, J., Kim, S., Jeong, D., Fu, X., and Cho, S.: Modeling nitryl chloride and its source and effect on gaseous and aerosol chemistry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3091, https://doi.org/10.5194/egusphere-egu23-3091, 2023.

Bromoform (CHBr₃) is one of the most important precursors of atmospheric reactive bromine with an atmospheric lifetime of ~20 days. Natural production, being the main source of oceanic CHBr₃, is high at the coasts and in open ocean upwelling regions due to production by macroalgae and phytoplankton. Although highly relevant for the future halogen burden and ozone layer in the stratosphere, the global bromoform production in the ocean and their emissions are still poorly constrained in observations and are mostly neglected in Earth System Model (ESM) climate projections.

Here, we show first model results of fully coupled ocean-atmosphere bromoform interactions in the Norwegian ESM (NorESM) with the ocean model BLOM and the ocean biogeochemistry component iHAMOCC for the CMIP6 historical period from 1850 to 2014.

Our results are validated using oceanic and atmospheric measurements listed in the HalOcAt (Halocarbons in the Ocean and Atmosphere) data base and show an overall good agreement with those observations in open ocean regions. The NorESM open ocean emissions of CHBr₃ are higher than previously published emission estimates from bottom-up approaches. Moreover, the emissions are mainly positive (sea-to-air fluxes) driven by the oceanic production, sea surface temperature and wind speed, dependent on season and location. However, during low-productive winter seasons, model results also show local negative fluxes (air-to-sea fluxes) in high latitudes, suggesting some oceanic regions to be a sink of atmospheric bromoform. Driving factors will be shown for different case studies, e.g. the tropical West Pacific, which is a hot spot for oceanic bromine delivery to the stratosphere.

How to cite: Booge, D., Tjiputra, J., Olivié, D., Quack, B., Schulz, M., and Krüger, K.: Global and regional marine bromoform emissions in a fully coupled ocean-atmosphere-model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12225, https://doi.org/10.5194/egusphere-egu23-12225, 2023.

Observational evidence shows the ubiquitous presence of short-lived halogens in the global atmosphere. This includes the biogenic contribution of organic very short-lived halocarbons as well as the abiotic source of inorganic halogens throughout heterogeneous recycling. All of these species are naturally emitted from the oceans, polar ice, and the biosphere, presenting a pronounced spatio-temporal source strength that controls the regional, vertical and seasonal distribution in the troposphere. In addition, anthropogenic emissions of reactive halogens, both organic and inorganic, have been identified in the atmosphere. Most notably, short-lived halogen emissions influence the oxidative capacity of the troposphere and consequently the concentration of ozone and methane. In this communication, we use the halogen version of CAM-Chem to evaluate how these interactions evolve across pre-industrial, present-day, and future climates under different halogen emission scenarios.

How to cite: Fernandez, R., Li, Q., Cuevas, C., Fu, X., Kinnison, D., Tilmes, S., Mahajan, A., Gomez-Martin, J. C., Iglesias-Suarez, F., Hossaini, R., Plane, J., Myhre, G., Lamarque, J.-F., and Saiz-Lopez, A.: Interactions between natural short-lived halogens and atmospheric oxidation capacity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14999, https://doi.org/10.5194/egusphere-egu23-14999, 2023.