ABSTRACT

Equivalent black carbon (BC) in surface air was measured using an aethalometer on Rishiri Island, northern Japan (45°07ʹ N, 141°12ʹ E), to examine temporal variations in BC between May 15, 2012 and May 8, 2013. Based on the negative relationship observed between BC and ²²²Rn during the diurnal cycle, the dry deposition velocity of BC was estimated to be between 0.23 and 0.42 cm s^–1. High BC events, lasting for hours, occurred from late October to April, and were caused by the long-range transport of air masses that had moved over, or near, high BC emission areas in China. In contrast, air masses associated with low BC events originated near the Sea of Okhotsk and the Bering Sea. The observed slope of the linear regression line between BC and CO (ΔC_BC/ΔC_CO) during high BC events was between 3.6 and 6.8 ng m^–3/ppb, except for an event on April 23, 2013 when the value of ΔC_BC/ΔC_CO decreased by 6.4 ng m^–3/ppb (i.e., from 12.0 ± 0.6 ng m^–3/ppb to 5.6 ± 0.5 ng m^–3/ppb). It is considered that the dry and wet deposition of BC during transport most likely contributed to the large decrease in values of ΔC_BC/ΔC_CO.