New chlorine species detected in the Arctic air

Active chlorine cycling has been known to play key roles in the depletion of surface ozone and the degradation of methane in the Arctic troposphere. However, a largely unexplored aspect entails the formation of chlorine oxyacids, such as chloric acid (HClO₃) and perchloric acid (HClO₄), has limited our full understanding of the atmospheric chlorine cycle and its associated environmental impacts. In a new study led by University of Helsinki, and published in the Nature Communications journal, scientists observed both gas-phase HClO₃ and HClO₄ for the first time in the ambient Arctic airmasses. Observations were collected at various locations above the Arctic Circle reaching from Greenland to Ny-Ålesund in Svalbard island and over the central Arctic Ocean during the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC) campaign. The work also proposes a novel plausible mechanism for the formation and loss of HClO₃ and HClO₄, providing evidence for chlorine oxyacids to be a previously unconsidered atmospheric sink for reactive chlorine in the Arctic environment. The existence of these new chlorine species in the atmosphere should be considered when evaluating the environmental impacts of chlorine chemistry in the Arctic.

Reference: Tham, Y.J., Sarnela, N., Iyer, S., et al., (2023). Widespread detection of chlorine oxyacids in the Arctic atmosphere. Nat. Commun., 14, 1769. https://doi.org/10.1038/s41467-023-37387-y