Mixing state, spatial distribution, sources and photochemical enhancement to sulfate formation of black carbon particles in the Arctic Ocean during summer

Abstract. Black carbon heats the atmosphere by absorbing solar radiation and regulates the radiation balance of the Earth. Specifically in the Arctic region, black carbon accelerates Arctic warming by simultaneously altering surface albedo. Nonetheless, assessing the climatic impacts of black carbon aerosols in the Arctic is challenging due to their considerable variability in temporal and spatial distribution, sources, and chemical composition. Black carbon particles (0.2–2 μm) in the Arctic Ocean were investigated using a ship-based single particle aerosol mass spectrometer from July to August 2017. In the central Arctic Ocean, near the Norwegian Sea-Iceland and the North Atlantic, biomass combustion is the predominant source of black carbon particles, constituting over 50 %, with a particularly high contribution exceeding 70 % in the central Arctic Ocean. Within the Chukchi Sea region, terrestrial transport from mid and low latitudes emerges as the primary source of black carbon particles, representing over 50 %, with biomass combustion and anthropogenic pollution sources each contributing around 25 %. Near Svalbard, biomass combustion sources and terrigenous transport stand out as the primary sources of black carbon particles, with their contributions being comparable. Furthermore, the ratio of sulfate to nitrate in black carbon particles was notably higher compared to that in sea salt particles. This ratio increased with elevated black carbon content and sunlight intensity, suggesting that Arctic black carbon particles substantially facilitated sulfate formation through photochemical processes. Such interactions could potentially modify the mixing state of Arctic black carbon particles and their radiative impacts.