Alteration of the microphysical properties of black carbon through transport in the boundary layer in East Asia
Atmospheric Chemistry and Physics Discussions
Ground-based measurements of black carbon (BC) were performed near an industrial source region in the early summer of 2014 and at a remote island in Japan in the spring of 2015. We report the temporal variations in the transport, size distributions, and mixing states of the BC-containing particles measured using a continuous soot monitoring system, a single particle soot photometer, and an aerosol chemical speciation monitor. The effects of aging on the growth of BC-containing particles were
... mined by comparing the ground-based observations between the near-source and remote island sites. Secondary formation of sulfate aerosol through gas- and cloud-phase reactions strongly affected the increases in BC coating (i.e., enhancement of cloud condensation nuclei activity) with air mass aging from the source to the outflow regions. The effects of the wet removal on the BC microphysics were elucidated by classifying the continental outflow air masses depending on the enhancement ratio of BC to CO (ΔBC&thinsp;/&thinsp;ΔCO) ratios as an indicator of the transport efficiency of BC. It was found that ΔBC&thinsp;/&thinsp;ΔCO ratios were controlled mainly by the rainout process during transport in the planetary boundary layer (PBL) on the timescale of 1&ndash;2 days. The meteorological conditions and backward trajectory analyses suggested that air masses strongly affected by rainout originated mainly from Southern China region (20º&ndash;35º&thinsp;N) during this season. Selective removal of large and thickly-coated BC-containing particles was found in air masses substantially affected by the rainout in the PBL, as predicted by Köhler theory. The size and water-solubility of BC-containing particles in the PBL can be altered by the rainout process as well as the condensation of non-BC materials.