Abstract

Brown Carbon (BrC) aerosols play a significant role in atmospheric radiative forcing, particularly in the Arctic where they could potentially contribute to surface warming. However, their regional variability and sources in the open ocean remain poorly understood. To address this, we conducted ship-based aerosol measurements aboard the R/V Mirai during the MR18-05C research cruise (October–December 2018), spanning the western North Pacific, Bering Sea, and Arctic Ocean. We examined BrC optical properties alongside PM2.5 chemical composition, trace gases, and meteorological conditions to assess its variability and sources. Our results reveal a drastic northward decline in BrC levels, with light absorption capability in the Bering Sea and the Arctic approximately 50% lower than those in the western North Pacific. The strongest BrC absorption was observed in regions influenced by crop residue burning in Northeast China. In the Arctic, BrC remained low as the main footprint is within the Arctic alongside limited BrC sources, although occasionally affected by long-range transport. Chemical composition analysis highlights biomass burning and fossil fuel emissions as dominant BrC sources in the western North Pacific. Solubility analysis indicated that BrC in the Arctic was predominantly water-soluble, increasing its susceptibility to wet scavenging. A strong high-pressure system (1027 ± 6.2 hPa) over the Arctic (November 9–17) led to aerosol accumulation, although BrC remained low. This study underscores the complex interplay between regional emissions, long-range transport, and atmospheric processing in regulating BrC distributions across latitudinal gradients. Our findings highlight the importance of source-region emissions and transport pathways in determining BrC fate in the Arctic, with implications for understanding its role in climate forcing.