Estimating Source Region Influences on Black Carbon Abundance, Microphysics, and Radiative Effect Observed Over South Korea

Abstract

East Asia is the strongest global source region for anthropogenic black carbon (BC), the mostimportant light-absorbing aerosol contributing to direct radiative climate forcing. To provide extendedobservational constraints on regional BC distributions and impacts, in situ measurements of BC wereobtained with a single particle soot photometer during the May/June 2016 Korean-United States Air Qualityaircraft campaign (KORUS-AQ) in South Korea. Unique chemical tracer relationships were associated with BCsourced from different regions. The extent and variability in vertical BC mass burden for 48 profiles over asingle site near Seoul were investigated using back trajectory and chemical tracer analysis. Meteorologicallydriven changes in transport influenced the relative importance of different source regions, impactingobserved BC loadings at all altitudes. Internal mixing and size distributions of BC further demonstrateddependence on source region: BC attributed to China had a larger mass median diameter (180 ± 13 nm) thanBC attributed to South Korea (152 ± 25 nm), and BC associated with long-range transport was less thicklycoated (60 ± 4 nm) than that sourced from South Korea (75 ± 16 nm). The column BC direct radiative effect atthe top of the atmosphere was estimated to be 1:0þ0:9 0:5W/m2, with average values for different meteorologicalperiods varying by a factor of 2 due to changes in the BC vertical profile. During the campaign, BCsourced from South Korea (≤31%), China (22%), and Russia (14%) were the most significant single-regioncontributors to the column direct radiative effect.