Characteristics of atmospheric black carbon and other aerosol particles over the Arctic Ocean in early autumn 2016: Influence from biomass burning as assessed with observed microphysical properties and model simulations.

We conducted ship-based measurements of marine aerosol particles (number concentration, size distribution, black carbon (BC), autofluorescence property, and PM2.5 composition) and trace gases (ozone (O3) and carbon monoxide (CO)) during a cruise of the R/V Mirai (23 August to 4 October 2016) over the Arctic Ocean, Northwest Pacific Ocean, and Bering Sea. Over the Arctic Ocean at latitudes >70°N, the averaged BC mass concentration was 0.7 ± 1.8 ng/m3, confirming the validity of our previously-reported observations (~1 ng/m3) over the same region during September 2014 and September 2015. The observed levels over the Arctic Ocean need to be used as a benchmark when testing the atmospheric transport models over the ocean, while they are substantially lower than those reported at Barrow (Utqiaġvik), a nearby ground-based station. We identified events with elevated BC mass concentrations and CO mixing ratios over the Arctic Ocean and Bering Sea as influenced by biomass burnings, with evidences from elevated levoglucosan levels, mixing states of BC particles, and particle size distributions. With WRF-Chem model simulations, we confirmed Siberian Forest fire plumes traveled over thousands of kilometers and produced substantially high BC and CO levels over the Bering Sea. The ΔBC/ΔCO ratios during these periods were estimated as ~1 ng/m3/ppbv, which are lower than those values reported, indicating that the results might have been affected by the wet removal process during transportation and/or by emission in smoldering conditions.