Size dependence of wet removal of black carbon aerosols during transport from the boundary layer to the free troposphere

Abstract

Size distributions of black carbon (BC) measured by aircraft over East Asia in spring 2009 were highly correlated with BC transport efficiency in air parcels uplifted from the planetary boundary layer to the free troposphere. The average single‐particle BC mass decreased with decreasing transport efficiency, which suggests that aerosols containing larger BC mass were removed more efficiently. This is the first successful observation of the size‐dependent wet removal of aerosols, qualitatively consistent with the Köhler theory. The size distribution of BC uplifted to the free troposphere with high efficiency was similar to the size distribution of BC in the planetary boundary layer. Conversely, the size distribution of BC uplifted with low efficiency was similar to that of background air in the free troposphere. We conclude that wet removal during upward transport is important in controlling the size distribution of BC in the free troposphere.