Abstract
Seasonal variation and origin of long-range transported carbonaceous aerosols from East Asia to the East China Sea were investigated. The mass concentrations of elemental carbon (EC), organic carbon (OC), particulate matter smaller than 2.5 μm (PM2.5) and gaseous CO were measured at the Cape Hedo Atmosphere and Aerosol Monitoring Station (CHAAMS) located on Okinawa, Japan, in 2004-2008. The concentrations of these chemical substances were simultaneously high during the spring and winter (EC: 0.14 - 0.19 μg C/m3, OC: 0.62 - 0.82 μg C/m3, PM2.5: 14.8 - 19.9 μg/m3, O3: 43 - 55 ppbv, CO: 183 - 221 ppbv) but low during summer (EC: 0.03 - 0.08 μg C/m3, OC: 0.28 - 0.44 μg C/m3, PM2.5: 9.85 - 14.8 μg/m3, O3: 14 - 23 ppbv, CO: 68 - 93 ppbv). It was postulated that pollutants were transported to CHAAMS by migratory high pressures and cold fronts from the Asian continent during the spring and winter, whereas a monsoon transported the oceanic air mass from the Pacific during the summer. The contributions of the carbonaceous aerosol concentrations from China were noticeably higher according to the EC, OC and emissions. The carbonaceous aerosol origin was identified by the OC/EC ratios and the correlation between the EC and OC. The OC/EC ratio was low during the spring and winter (OC/EC: 5.7 - 8.0), but high during the summer (OC/EC: 10.2 - 18.9). These results implied a similar conclusion, i.e., the anthropogenic pollutants were transported to CHAAMS from Asia in the spring and winter, whereas in the summer, a monsoon transported the oceanic clean air mass. A photochemical oxidation reaction was also identified from the high OC/EC ratio. Based on the back trajectories of the air masses, the correlations between the OC/EC showed that the origin of the carbonaceous aerosols in North China (NC) was different from South China (SC). It is also suggested that origin of the carbonaceous aerosols in Japan (JP) and Korea (KR) have an influence on the formations of the secondary organic carbon (SOC) via the reactions of the VOCs, causing the OC fraction to increase.
