Chemical characteristics of long-range-transported fine particulate matter at Gosan, Jeju island, in the spring and fall of 2008, 2009, 2011, and 2012

Abstract

Carbonaceous species (organic carbon [OC] and elemental carbon [EC]) and inorganic ions of particulate matter less than 2.5 μm (PM2.5) were measured to investigate the chemical characteristics of long-range-transported (LTP) PM2.5at Gosan, Jeju Island, in Korea in the spring and fall of 2008-2012 (excluding 2010). On average, the non-sea-salt (nss) sulfate (4.2 μg/m3) was the most dominant species in the spring, followed by OC (2.6 μg/m3), nitrate (2.1 μg/m3), ammonium (1.7 μg/m3), and EC (0.6 μg/m3). In the fall, the nss-sulfate (4.7 μg/m3) was also the most dominant species, followed by OC (4.0 μg/m3), ammonium (1.7 μg/m3), nitrate (1.1 μg/m3), and EC (0.7 μg/m3). Both sulfate and OC were higher in the fall than in the spring, possibly due to more common northwest air masses (i.e., coming from China and Korea polluted areas) and more frequent biomass burnings in the fall. There was no clear difference in the EC between the spring and fall. The correlation between OC and EC was not strong; thus, the OC measured at Gosan was likely transported across a long distance and was not necessarily produced in a manner similar to the EC. Distinct types of LTP events (i.e., sulfate-dominant LTP versus OC-dominant LTP) were observed. In the sulfate-dominant LTP events, air masses directly arrived at Gosan without passing over the Korean Peninsula from the industrial area of China within 48 hr. During these events, the aerosol optical depth (AOD) increased to 1.63. Ionic balance data suggest that the long-range transported aerosols are acidic. In the OC-dominant LTP event, a higher residence time of air masses in Korea was observed (the air masses departing from the mainland of China arrived at the sampling site after passing Korea within 60-80 hr).