Semi-continuous Measurements of PM 2.5 OC and EC at Gosan: Seasonal Variations and Characteristics of High-concentration Episodes

Abstract

At Gosan ABC superstation in Jeju Island, we measured organic carbon (OC) and elemental carbon (EC) in PM2.5 from October 2009 to June 2010 using a Sunset Laboratory Model-4 Semi-Continuous OC/EC Field Analyzer. It employs TOT (Thermal-Optical-Transmittance) method with NIOSH 5040 protocol and enables to continuously monitor OC and EC concentrations with 1-hour time resolution. The mean values of OC and EC for the entire period of measurements were 2.1±1.4 μg/m3 and 0.7±0.6 μg/m3, respectively. The OC/EC ratio was 3 and EC accounted 25±2.1% of total carbon (TC, TC=OC+EC). Although OC and EC showed similar trend in seasonal variation, the ratio of OC to EC was the highest in early summer when temperature was the highest and the air was affected by biomass burning in the southern part of China. In winter, the high OC and EC concentrations were likely influenced by increased coal combustion from residential heating. The high OC and EC concentrations were observed during events such as haze, dust, and the combination of the two. During the haze events, OC and EC were enhanced with increase in PM10, PM2.5, SO2, and NO2 with broad maxima. When dust occurred, both OC and EC started decreasing after reaching their maxima a couple of hours before PM10 maximum. The peak separation of carbonaceous species and aerosol masses with time was more noticeable when haze event was followed by dust plume. These results confirm that OC and EC are key components of haze occurring in the study region.