Widespread detection of chlorine oxyacids in the Arctic atmosphere

Abstract

Chlorine radicals are strong atmospheric oxidants known to play an important role in the depletion of surface ozone and the degradation of methane in the Arctic troposphere. Initial oxidation processes of chlorine produce chlorine oxides, and it has been speculated that the final oxidation steps lead to the formation of chloric (HClO3) and perchloric (HClO4) acids, although these two species have not been detected in the atmosphere. Here, we present atmospheric observations of gas-phase HClO3 and HClO4. Significant levels of HClO3 were observed during springtime at Greenland (Villum Research Station), Ny-Ålesund research station and over the central Arctic Ocean, on-board research vessel Polarstern during the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC) campaign, with estimated concentrations up to 7 × 106 molecule cm−3. The increase in HClO3, concomitantly with that in HClO4, was linked to the increase in bromine levels. These observations indicated that bromine chemistry enhances the formation of OClO, which is subsequently oxidized into HClO3 and HClO4 by hydroxyl radicals. HClO3 and HClO4 are not photoactive and therefore their loss through heterogeneous uptake on aerosol and snow surfaces can function as a previously missing atmospheric sink for reactive chlorine, thereby reducing the chlorine-driven oxidation capacity in the Arctic boundary layer. Our study reveals additional chlorine species in the atmosphere, providing further insights into atmospheric chlorine cycling in the polar environment.

Reactive Chlorine Species Advancing the Atmospheric Oxidation Capacities of Inland Urban Environments

“…Thus, more research on reactive chlorine should be conducted in the future to explore its role in photochemistry, including more long-term measurements, multigenerational oxidation mechanisms of the Cl radicals, and their sources. In the Arctic boundary layer, active chlorine cycling is acknowledged to play a key role in the depletion of the surface O 3 and the formation of chloric acid (HClO 3 ) and perchloric acid (HClO 4 ) . In coastal regions, the ratio of O 3 to the VOCs is another key parameter used in determining the impacts of chlorine activation; i.e., higher O 3 levels tend to sustain cycling by increasing the fraction of Cl atoms that are converted to ClO .…”

Perchlorate in Year‐Round Antarctic Precipitation

“…Oxidants, for example, O 3 , BrO, and OH, participate in almost all the proposed formation mechanisms of atmospheric $${{\text{ClO}}_{4}}^{-}$$ (Carrier & Kounaves, 2015; Dasgupta et al., 2005; Estrada et al., 2021; W. A. Jackson et al., 2018; Kang et al., 2006; Tham et al., 2023). Can $${{\text{ClO}}_{4}}^{-}$$ production in the Antarctic troposphere be controlled by oxidant levels?…”

“…Tropospheric processes mainly comprise the oxidation of Cl-containing precursors (e.g., chloride (Cl − ) and oxy-chlorine species) by oxidants such as ozone (O 3 ), hydroxyl radical (OH) and BrO (Estrada et al, 2021;W. A. Jackson et al, 2018;Kang et al, 2006Kang et al, , 2009Rao et al, 2010;Tham et al, 2023), which may occur through oxidation of reactive chlorine (e.g., Cl atom) formed through photolysis of Cl-containing precursors (W. A. Jackson et al, 2018;Tham et al, 2023) or through direct oxidation of Cl − without light (Kang et al, 2008).…”

“…A. Jackson et al, 2018;Kang et al, 2006Kang et al, , 2009Rao et al, 2010;Tham et al, 2023), which may occur through oxidation of reactive chlorine (e.g., Cl atom) formed through photolysis of Cl-containing precursors (W. A. Jackson et al, 2018;Tham et al, 2023) or through direct oxidation of Cl − without light (Kang et al, 2008). Lightning also plays a significant role in tropospheric 𝐴𝐴 ClO4 − formation (Dasgupta et al, 2005;Parker et al, 2008;Rao et al, 2012); however this formation pathway can be considered negligible in Arctic or Antarctica due to nearly no lightning in these regions (Virts et al, 2013).…”

Chlorine Oxyacids Potentially Contribute to Arctic Aerosol Formation

“…All clusters with 1 sulfuric acid monomer present were included in the monomer concentration of sulfuric acid, which corresponds to experimentally observed concentrations. Three different temperatures were tested: 253.15 K, 263.15 K, and 278.15 K, while the first two are typical temperatures during the Greenland and MOSAiC measurements, the last one was chosen in order to be comparable to our previous studies. ,,− The monomer concentrations were kept constant at the values presented in Table . Chloric, perchloric, and sulfuric acid concentrations were chosen based on the study by Tham et al Due to a lack of measurements, we had to estimate low and high amine concentrations in the Arctic in the winter and early spring.…”