Halogenated volatile organic compounds (XVOCs) are volatile hydrocarbons that have at least one halogen atom. These substances are of global importance because their relatively long atmospheric lifetimes enable transport of halogen atoms to the stratosphere leading to stratospheric ozone depletion. Since the regulation of anthropogenic XVOC emissions through the Montreal Protocol and subsequent amendments, the importance of naturally formed XVOCs has been increasing. Chloromethane (CH₃Cl), for example, represents the largest natural source of chlorine in the stratosphere, currently contributing to approximately 16% of stratospheric ozone depletion, with plants suggested to be its major source. Other XVOCs like Chloroform (CHCl₃) can influence atmospheric chemistry more on a local scale due to their shorter atmospheric lifetimes.

In this work, we present the implementation of an instrumentational setup for long-term in-situ XVOC monitoring at the Amazon Tall Tower Observatory (ATTO) site. The 325 m tall tower, located in the pristine Amazon rainforest (circa 150 km NE of Manaus, Brazil), enables measurements of natural XVOC emissions almost free of anthropogenic influence due to its remote location.

The analytical setup consists of the tower inlet system and a Multi-Capillary Column Trapping System (MCCTS) coupled to GC-MS. Here we show several days of preliminary data for methyl chloride, isoprene and several CFC species as a proof of concept. Furthermore, we examine the applicability of simultaneous CFC measurements as a “natural internal standard” for the correction of systematic errors like MS sensitivity changes.

The presented analytical method is able to provide data in form of atmospheric mixing ratios of the desired XVOC compounds at four different heights (ground level, 80 m, 150 m and 320 m) with a time resolution of approximately two hours per height. It has the potential to open up new opportunities to better quantify the XVOC net production and consumption of the Amazon Basin ecosystem and to understand the underlying processes, especially with respect to future ecosystem transformations due to climate and land use changes.

How to cite: Hartmann, C., Byron, J., Pugliese, G., Lelieveld, J., and Williams, J.: Development of analytical method to measure halogenated volatile organic compounds in the Amazon rainforest, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4642, https://doi.org/10.5194/egusphere-egu24-4642, 2024.

This study explores the role of snowpack in polar boundary layer chemistry, especially as a direct source of reactive bromine (BrO_X=BrO+Br) and nitrogen (NO_X=NO+NO₂) in the Arctic springtime. Surface snow samples were collected daily from a Canadian high Arctic location at Eureka, Nunavut (80°N, 86°W) from the end of February to the end of March in 2018 and 2019. The snow was sampled at several sites representing distinct environments: sea ice, inland close to sea level, and a hilltop ~600 m above sea level.  At all sites, snow sodium and chloride concentrations increase by almost tenfold from the top 0.2 cm down to a depth of ~1.5 cm. Surface snow bromide at sea level is significantly enriched, indicating a net sink of atmospheric bromine. Moreover, surface snow bromide at sea level has an increasing trend over the measurement period, with mean slopes of 0.024 mM d^-1 in the 0-0.2 cm layer and 0.016 mM d^-1 in the 0.2-0.5 cm layer. Surface snow nitrate at sea level also shows a significant increasing trend, with mean slopes of 0.27, 0.20, and 0.07 mM d^-1 in the top 0.2 cm, 0.2-0.5 cm, and 0.5-1.5 cm layers, respectively. Using these trends, an integrated net deposition flux of bromide of (1.01±0.48)×10⁷ molecules cm^-2 s^-1 and an integrated net deposition flux of nitrate of (2.6±0.37)×10⁸ molecules cm^-2 s^-1 were derived. In addition, the surface snow nitrate and bromide at inland sites were found to be significantly correlated (R=0.48-0.76) with the [NO₃^-]/[Br^-] ratio of 4-7 indicating a possible acceleration effect of reactive bromine in atmospheric NO_X-to-nitrate conversion. This is the first time such an effect has been seen in snow chemistry data obtained with a sampling frequency as short as one day.

BrO partial column (0-4 km) data measured by MAX-DOAS show a decreasing trend in March 2019, which agrees with the derived surface snow bromide deposition flux. This indicates that bromine in the Eureka atmosphere and surface snow did not reach a photochemical equilibrium state and that the photochemical release flux of reactive bromine from snow must be a weak process and smaller than the derived bromide deposition flux of ~1×10⁷ molecules cm^-2 s^-1.

How to cite: Yang, X., Strong, K., Criscitiello, A., Santos-Garcia, M., Bognar, K., Zhao, X., Fogal, P., Walker, K., Morris, S., and Effertz, P.: Surface snow bromide and nitrate at Eureka, Canada in early spring and implications for polar boundary layer chemistry, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5922, https://doi.org/10.5194/egusphere-egu24-5922, 2024.

Atmospheric methane is a potent greenhouse gas that is photochemically active. The addition of chlorine to the atmosphere has been proposed to mitigate global warming through methane reduction by increasing its chemical loss. However, the potential environmental impacts of such climate mitigation remain unexplored. We explore the possible effects of increasing reactive chlorine emissions on the methane budget, atmospheric composition and radiative forcing. Due to non-linear chemistry we found that achieving effective methane reduction require a minimum 3-fold increase in chlorine atoms compared to present-day levels. Our highest scenario, 50-fold present-day chlorine levels, led to a reduction of the surface temperature by 0.6°C in the year 2050. Beyond the direct effects on methane and temperature, our results show significant alterations in other climate forcers, particularly a large decrease in tropospheric ozone. This translates into a reduction in radiative forcing of a similar magnitude as of the methane removed. Additionally, the Antarctic stratosphere ozone burden during September and October was reduced by up to 40% with the highest chlorine addition. Consequently, the implementation of such strategies requires careful consideration of various factors, including the quantity and method of chlorine addition, as well as potential environmental impacts on air quality and ocean acidity. 

How to cite: Meidan, D., Li, Q., Hess, P., Añel, J. A., Cuevas, C. A., Doney, S., Fernandez, R. P., van Herpen, M., Höglund-Isaksson, L., Johnson, M. S., Kinnison, D. E., Lamarque, J.-F., Röckmann, T., Mahowald, N. M., and Saiz-Lopez, A.: Global environment impacts of enhanced chlorine emissions for methane removal through chemistry-climate interactions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8488, https://doi.org/10.5194/egusphere-egu24-8488, 2024.

Hydrofluorocarbon-134a (HFC-134a) has been experiencing an annual increase in global emissions and atmospheric concentration in recent years, as a major substitute for ozone-depleting substances (ODSs). It has attracted considerable global attention owing to its double environmental effects, including high global warming potential and degradation to form trifluoroacetic acid (TFA). There are discrepancies in the results of existing top-down and bottom-up studies, and existing studies have only estimated the total HFC-134a emissions at national or regional scales. The lack of methods for building and verifying high-spatial-resolution emissions inventories makes it difficult to analyze the spatial distribution of emissions and regional contributions, as well as to identify emission hotspot grids. This study utilized emission factors and an atmospheric dispersion model to establish a methodology for calculating and validating a gridded emission inventory of HFC-134a, and evaluated its dual environmental impacts. This study focused on China and calculated a gridded emission inventory of HFC-134a for the period from 1995 to 2020. The results showed that the banks and emissions of HFC-134a increased from 0.9 kt and 0.1 kt yr^-1 in 1995 to 301 kt (273-332 kt) and 48 kt yr^-1 (39-56 kt yr-1) in 2020, respectively. Guangdong, Jiangsu, and Shandong provinces in eastern China had the largest cumulative emissions, with a total cumulative emission amount of 98 kt, accounting for 28% of the national emissions, and were also the provinces where the hotspot grids were mainly distributed. The high spatial resolution emission inventories can provide important input data for atmospheric models to simulate transport and transformation processes and assess environmental impacts, thus improving the accuracy of modelling and prediction. In addition, prediction results showed that if HFC-134a was phased out solely in accordance with the emission reduction requirements of the Kigali Amendment, there would still be HFC-134a banks and emissions in China by the year 2060. If emissions were reduced according to the carbon-neutral emission reduction path proposed in this study to meet a high consumption demand for HFC-134a, it was feasible to achieve nearly zero emissions in 2060. Nevertheless, if HFO-1234yf and R-513A were selected as substitutes for HFC-134a, it could result in the production of more TFA through atmospheric degradation, which could have an adverse impact on the aquatic ecosystem and plants. Therefore, it is necessary to actively explore more environmentally friendly alternatives in the future.

How to cite: Wu, J., Wang, T., Ding, S., An, M., Liu, Z., and Peng, L.: Establishment and verification of HFC-134a-gridded emission inventory in China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8981, https://doi.org/10.5194/egusphere-egu24-8981, 2024.

Reactive halogens compounds (i.e., those containing bromine, iodine, chlorine) are known to be key species for the oxidizing capacity of the atmosphere affecting e.g. the lifetime of relevant species such ozone, HO_x or NO_x and also to have an impact on the climate through interactions with other trace gases and aerosols.
In the polar regions reactive halogens play a particular role since e.g. the auto-catalytic release of bromine from sea ice into the atmosphere may lead to the depletion of tropospheric ozone even below instrumental detection limit and, also, to the deposition of toxic mercury into the polar ecosystem.
In order to infer vertical profiles of relevant tropospheric trace gases, within the framework of several nationally funded projects (including the current GARDENIA project) and in collaboration with the Argentinian National Antarctic Direction, INTA has being performing multi-axis DOAS (MAXDOAS) observations from Antarctica for nearly a decade. One of the gases retrieved through the MAXDOAS technique is bromine monoxide (BrO), a reactive form of bromine.
The work presented herein expands the 1-year study of Prados-Roman et al. (2018) to a 8-year study of the presence of tropospheric BrO at two research sites in Antarctica: Belgano II (77°52' S, 34°7' W) and Marambio (64°13' S, 56°37' W). We will present tropospheric BrO data from the two research sites that expands from 2015 to last year 2023, with values as high as nearly 40 pmol/mol. We will discuss the tropospheric BrO vertical and  latitudinal distribution as well its seasonal evolution throughout all these years.
Note that a similar work but based on observations of iodine monoxide from Antarctica will be presented at EGU2024 in the work of Puentedura et al. (2024).

How to cite: Prados-Roman, C., Gómez-Martín, L., Puentedura, O., Adame, J. A., Navarro-Comas, M., Ochoa, H., and Yela, M.: Long-term (2015-2023) observations of tropospheric BrO from two research sites in Antarctica, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9794, https://doi.org/10.5194/egusphere-egu24-9794, 2024.

The tropospheric distribution of iodine monoxide (IO) in Antarctica remains an open question, as there are some uncertainties concerning, for example, its geographical and vertical distribution. Accurate long-term measurements of IO are important to understand its role in the tropospheric composition of this region, where continuous ground-based observations of IO are very rare and satellite observations have some limitations.

INTA's Antarctic activities include MAXDOAS measurements since 2011 in the framework of several nationally funded projects such as MARACA, VIOLIN, HELADO, VHODCA and currently GARDENIA. The collaboration with the Argentinean National Antarctic Directorate has allowed MAXDOAS measurements at three different locations: Ushuaia (54ºS), located in Tierra del Fuego and at the Antarctic stations of Marambio (64ºS) and Belgrano (78ºS). This paper presents the vertical distribution of tropospheric IO obtained from MAXDOAS measurements at the aforementioned sites over a nine-year period (2015-2023).

Note that a similar work but based on observations of bromine monoxide from Antarctica will be presented here at EGU2024 in the work of Prados-Román et al. (2024).

How to cite: Puentedura, O., Prados-Roman, C., Gomez-Martin, L., Navarro-Comas, M., Ochoa, H., and Yela, M.: Tropospheric Iodine monoxide distribution from MAXDOAS observations at three Antarctic stations during the 2015-2023 period., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10042, https://doi.org/10.5194/egusphere-egu24-10042, 2024.

1,2-Dibromotetrafluoroethane (C₂Br₂F₄, Halon-2402, H-2402) is used as a fire suppressant due to its stability because it maintains a liquid state at room temperature with a relatively high boiling point. However, H-2402, containing bromine (Br), was identified as a potent ozone-depleting substance, with a destructive capacity six times higher than that of CFC-11. Therefore, under the Montreal Protocol, its production and consumption were phased out globally in 2010, with developed countries starting their phase out in 1994. Russia, the primary producer of H-2402, reportedly ceased production after 2000. For essential uses where no alternatives are available (e.g., military fire extinguishers, oil and gas pipelines), existing or recycled supplies of H-2402 are permitted to be used. Despite H-2402 being under strict international regulation, accurate reporting and statistical information on essential production and consumption by countries remain limited.

This study analyzes the atmospheric mole fractions records of H-2402 measured from 2008 to 2020 at Gosan station, South Korea. While the background mole fractions of H-2402 at Gosan station are gradually decreasing at -0.01 ppt/yr, similar to the global decreasing trend, high pollution cases were continuously observed throughout the entire period. Also, the frequency of occurrence also increased by more than three times in 2020 compared to 2008. This increase in pollution signals, not observed at major Northern Hemisphere background monitoring stations (such as Mace Head, Trinidad Head, and Jungfraujoch), suggests potential regional emissions in eastern Asia. Based on long-term atmospheric observations, and a combined analysis using the Lagrangian particle dispersion model (FLEXPART) and the Bayesian inverse framework (FLEXINVERT+), we have estimated the annual regional emissions in eastern Asia. We present observation-based results on the long-term, regional-scale variability of H-2402 emissions over eastern Asia and their significant contributions from a global perspective.

How to cite: Choi, H., M. Western, L., Kim, J., Mühle, J., Thompson, R., Lee, G., K. Salameh, P., M. Harth, C., F. Weiss, R., Rigby, M., and Park, S.: Mysterious emissions of Halon-2402 in eastern Asia drive the global trend, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13726, https://doi.org/10.5194/egusphere-egu24-13726, 2024.

Chloromethane (CH₃Cl, average ambient mixing ratio 546 ppt (1)) and Bromomethane (CH₃Br, average ambient mixing ratio 6.52 ppt (1)) are the most abundant chlorine-, respective bromine-containing atmospheric trace gases from natural origin. Due to their relatively long tropospheric lifetimes (0.9 y; 0.8 y respectively (2)), they are significant carriers of chlorine and bromine into the stratosphere, where they are photolyzed and contribute to the catalytic destruction of ozone. Chloromethane is mainly emitted by tropical vegetation and soils, biomass burning and from oceans. Vegetation and soils have been shown to act as both, source and sink for Chloromethane. Bromomethane has anthropogenic and biogenic sources, including oceans, fumigation, biomass and fossil fuel burning, crops and vegetation. For both methyl halides the known tropospheric sinks, such as reaction with hydroxyl radicals, loss to soils and oceans, and loss to the stratosphere, do not balance the currently known sources. In particular the strengths of the tropical sources still have substantial uncertainties. Due to the Montreal Protocol, anthropogenic emissions of chlorine and bromine compounds are declining. Therefore, biogenic contributions will become an even more important fraction of the global budget in the following decades. A better understanding of the mechanisms behind emission and tropospheric distribution of Chloro- and Bromomethane is essential to improve predictions of future stratospheric ozone levels.

Here, we present the first airborne measurements of Chloromethane and Bromomethane over a tropical forest covering altitudes from the planetary boundary layer to the upper troposphere (300 – 14000 m). The measurements were conducted in Dec 2022 and Jan 2023 over the Amazon Rainforest with the German research aircraft HALO (High Altitude Long Range) in the scope of the CAFE-Brazil campaign. Chloromethane, Bromomethane and other Halocarbons and VOC were measured with Fast GC-MS with a time resolution of 3 minutes. On average elevated levels of both species were found in the boundary layer. Interestingly, the vertical distribution of both compounds also showed a layer with elevated mixing ratios in the upper troposphere, generating a C-shaped profile. The mean Chloromethane mixing ratio reached a maximum of 590 ± 30 ppt between 11 - 12 km altitude, whereas for Bromomethane the maximum appears to be higher than 14 km (where 11.8 ± 1.9 ppt were observed) and thus outside the covered altitude range. The high local convective activity and that of the more distant ITCZ may explain these observations. Surprisingly, high variability of mixing ratios in the boundary layer (300 – 1000 m) with seasonal and regional trends for both methyl halides was observed. Chloromethane mixing ratios between 499 and 686 ppt were observed, in agreement with earlier works which report that the rainforest (including vegetation and soil) can act as source and sink of Chloromethane. Bromomethane mixing ratios in the boundary layer varied between 6.0 to 20.9 ppt, indicating the rainforest to be a source of Bromomethane.

(1) World Meteorological Organization (WMO). Scientific Assessment of Ozone Depletion: 2022. Geneva; 2022. Report No.: 278.

(2) World Meteorological Organization (WMO). Scientific Assessment of Ozone Depletion: 2018. Geneva; 2018. Report No.: 58.

How to cite: Krumm, B., Ernle, L., Lelieveld, J., and Williams, J.: Vertical and spatial distribution of Chloromethane and Bromomethane from boundary layer to upper troposphere over the Amazon rainforest, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14827, https://doi.org/10.5194/egusphere-egu24-14827, 2024.

Halogens in volcanic plumes are important for both volcanic and environmental research. For example, changes in the composition of the volcanic plume can be an indication of changes in the activity of the volcano. Volcanic emissions consist mainly of emitted H₂O, CO₂ and SO₂ and are rapidly mixed with surrounding background atmosphere. Additionally, HF, HCl and HBr are also significant constituents of volcanic emissions.

The halogens are of particular interest for atmospheric chemistry. They are oxidized by mixing with the atmosphere. In this context, BrO should be mentioned as it is one of the oxidation products and like SO₂, can be measured spectroscopically using remote sensing technique and therefore making it nearly ideal for surveillance of volcanoes. However only, if the oxidation process is understood, the composition of the volcanic plume at the emission site can be traced and thus possibly the changes in volcanic activity can be understood.

Furthermore, these results are essential for the improvement of the atmospheric impact of volcanic halogens.

Currently, several methods are used to detect the various halogen compounds. Remote sensing methods exist for only a few (in general BrO, OClO, HCl, HF). We use in-situ sampling methods such as cis-Stilbene coated syringe filter and aqueous alkaline traps to collect reactive and total halogen species, respectively.

In this presentation, we will show quantitative results of samples taken in July 2022, June 2023 and in August 2023 for Cl₂, Br₂, BrCl, total bromine and sulfur from measurements of the Bocca Nuova and South East crater plume, Mt. Etna, Italy using UAV based in situ measurements in various distances to those emission sources. The results confirm the increase of reactive bromine and show for the first time the differentiation into Cl₂, Br₂, BrCl and total bromine and sulfur. Also BrO/SO₂ values analyzed from DOAS measurements taken further downwind during the campaign will be presented.

How to cite: Geil, B., Bobrowski, N., Karbach, N., Kuhn, J., Nies, A., Roberts, T., Hoor, P., and Hoffmann, T.: Halogen activation in volcanic plumes: Studies at Mt Etna (Italy) 2022 and 2023, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14976, https://doi.org/10.5194/egusphere-egu24-14976, 2024.

Volcanoes contribute as a natural source to the global emission of mercury into the atmosphere. The emission of mercury takes place mainly in the gas phase, predominately as elemental mercury. But, several observations show different degrees of mercury oxidation in early-stage volcanic plumes. During the first seconds of volcanic plume evolution, hot magmatic gases mix with the atmosphere and the in-mixture of atmospheric oxygen triggers fast oxidation processes. These change the chemical composition of the volcanic plume drastically and lead to the conversion of hydrogen halides (e.g. hydrogen bromide and hydrogen chloride) into reactive halogen species. These reactive halogen species are well known to interact with mercury and promote the oxidation of elemental mercury towards divalent gaseous mercury.

We present model studies investigating the first seconds of the evolution of a volcanic plume assessing the degree of mercury oxidation through reactive halogen chemistry. We utilize a new chemical box model that simulates chemical kinetics alongside cooling and dilution of the plume. The model is based on a chemical combustion mechanism coupled to an atmospheric chemistry mechanism, including sub-mechanisms for reactive halogens and mercury.  It shows that high-temperature halogen chemistry can potentially cause an oxidation of mercury in the percent range depending on emission temperature and mixing scenario. We compare these model calculations to mercury speciation measurements performed in near-source plumes at Mt Etna and Vulcano island in August/September 2023, where we find a relative abundance of divalent mercury of 5% and 37%, respectively. As well as showing evidence for rapid mercury oxidation, the field-observations at Vulcano indicate the potential for subsequent plume processes to cause mercury reduction.

Model simulations in combination with field-measurements illustrate a complex behavior of volcanic mercury and halogens going from the hot emission to the cooled plume.

How to cite: Roberts, T., Nies, A., Kuhn, J., Geil, B., Terray, L., and Sonke, J.: Assessment of the potential of high temperature halogen chemistry in volcanic plumes for the oxidation of mercury, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16447, https://doi.org/10.5194/egusphere-egu24-16447, 2024.