| Summary: | International audience During the ACCESS airborne campaign in July 2012, extensive boreal forest fires resulted in significant aerosol transport to the Arctic. A 10 day episode combining intense biomass burning over Siberia and low-pressure systems over the Arctic Ocean resulted in efficient transport of plumes containing black carbon (BC) towards the Arctic, mostly in the upper troposphere. A combination of in situ airborne observations, satellite analysis and WRF- Chem simulations are used to understand the vertical and horizontal transport mechanisms of BC with a focus on the role of wet removal.During transport to the Arctic region, a large fraction of BC particles are scavenged by two wet deposition processes, namely wet removal by large-scale precipitation and removal in wet convective updrafts, with both processes contributing almost equally to the total accumulated deposition of BC. Our results underline that applying a finer horizontal resolution (40 vs 100km) improves the model performance, as it significantlyreduces the overestimation of BC levels observed at a coarser resolution in the mid- troposphere. According to the simulations at 40km, the transport efficiency of BC (TEBC) in biomass burning plumes is about 60%, which is impacted by small accumulated precipitation along trajectory (APT) (1mm). In contrast TEBC is very small (<30%) and APT is larger (5−10 mm) in plumes influenced by urban anthropogenic sources and flaring activities in Northern Russia, resulting in transport to lower altitudes.TEBC due to grid scale precipitation is responsible for a sharp meridional gradient in the distribution of BC concentrations. Wet removal in subgrid parameterized clouds (cumuli) is the cause of modeled vertical gradient of TEBC , especially in the mid-latitudes, reflecting the distribution of convective precipitation, but is dominated in the Arctic region by the grid-scale wet removal associated with the formation of stratocumulus clouds in the PBL that produced frequent drizzle.
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