Comment on egusphere-2025-5807

Abstract. Using ship-based MAX-DOAS during China's 12th Arctic Scientific Expedition, we conducted spatial observations of NO2, HCHO, BrO, and IO along the round-trip cruise from Shanghai to the Arctic, centering on two core scientific objectives: validating the polar applicability of satellite data and identifying reactive halogen source regions with their driving mechanisms. ship-based measurements were compared with satellite-derived atmospheric products from TROPOMI, GEMS, and GOME-2. High-probability potential BrO sources were concentrated in western Greenland, the seas north of North America, and the Arctic sea ice edge zone, confirming sea ice-related photochemical processes as BrO's primary formation mechanism. For IO, a strong positive correlation was found with chlorophyll a concentrations. Biogenic IO sources were mainly located in phytoplankton-enriched regions, including the Bering Strait, southern Greenland, and coastal North Atlantic waters, verifying the key role of marine biological processes in IO production. Comparative analysis showed distinct spatial differences in potential source regions: BrO was associated with sea-ice-covered areas, while IO was linked to mid-to-low latitude coastal biologically active zones. Nevertheless, the two species shared the "ice-sea-atmosphere" exchange interface in the sea ice edge zone, resulting in a moderate correlation. This study provides critical in-situ validation for satellite data of multiple pollutants in the Arctic via ship-based mobile observations. It clarifies the sea ice-coupled formation mechanism of BrO and the biogenic-driven nature of IO, with results offering important data support for optimizing polar atmospheric chemistry models and global climate assessments.