Characteristics of PM2.5 haze episodes revealed by highly time-resolved measurements at an air pollution monitoring supersite in Korea

Abstract

Hourly measurements of PM2.5, organic and elemental carbon (OC and EC), inorganic ionic species, and elemental constituents were made between February 1 and March 31, 2011, at a South Area Supersite at Gwangju, Korea. Over the two-month study period, daily PM2.5 mass concentration exceeded the 24-hr average Korean NAAQS of 50.0 μg/m3 on 20 days, of which two pollution episodes (episodes I and II) are investigated. Episode I (February 01-08) is associated with regional pollution along with wild fire smoke emissions over southern China, and also characterized by high CO/NOx ratios and high K+ concentrations. While episode II (March 11-12) is characterized by locally produced pollution with low CO/NOx ratios, and broad variations in OC, EC, and NO3- concentrations. For episode I, the 1-hr PM2.5 mass concentration ranged from 27 to 159 μg/m3 with a mean of 88 μg/m3. Although a low OC/EC ratio (3.4) was observed for February 04-05 when high K+ concentrations occurred, significant linear relationships between EC - OC (R2 = 0.82), OC - K+ (R2 = 0.77), and K+ - K+/OC (R2 = 0.77) suggest the contribution of carbonaceous aerosols from long-range transport of biomass burning plumes occurring in the southern regions of China during episode I, as well as local traffic emissions. For episode II, the hourly PM2.5 mass concentration ranged from 23 to 116 μg/m3 with a mean of 78 μg/m3. Hourly maximum contributions of SO42- and NO3- to the PM2.5 mass were 54 and 66%, respectively. An elevated NO3- concentration was observed along with high OC and EC concentrations, suggesting the influence of local emissions. The pattern of SO42- variations in relation to wind direction and the strong correlation between SO2 and SO42- suggest local SO2 emissions were likely an important source of SO42- at the site. © Taiwan Association for Aerosol Research.