Pollution Characteristics Of Pm2.5 Observed During Winter And Summer In Baengryeongdo And Seoul

Hourly measurements of PM2.5 mass, organic and elemental carbon (OC and EC), and water-soluble ionic species were made at the air quality intensive monitoring stations in Baengryeongdo (BR) and Seoul (SL) during the winter (December 01 similar to 31, 2013) and summer (July 10 similar to 23, 2014) periods, to investigate the increase of PM2.5 and secondary ionic species and the reasons leading to their increase during the two seasons.During winter, PM2.5 and its major chemical species concentrations were higher at SL than at BR. Contribution of organic mass to PM2.5 was was approximately 1.7 times higher at BR than at SL, but the NO3- contribution was two times higher at SL. Total concentration of secondary ionic species (SO42, NO3, and NH4+) at BR and SL sites accounted for 29.1 and 40.1% of PM2.5, respectively. However, during summer, no significant difference in chemical composition of PM2.5 was found between the two sites with the exception of SO42-. Total concentration of the secondary ionic species constituted on average 43.9% of PM2.5 at BR and 53.0% at SL. A noticeable difference in chemical composition between the two sites during summer was attributed to SO42-, with approximately two-fold concentration and 10% higher contribution in SL.Low wind speed and high relative humidity were important factors in secondary formation of water-soluble ionic species during winter at SL, resulting in PM2.5 increase. While the secondary formation during summer was attributed to strong photochemical processes in daytime and high relative humidity in nighttime hours. The increase of PM2.5 and its secondary ionic species during the winter haze pollution period at SL was mainly caused either by long-range transport (LTP) from the eastern Chinese regions, or by local pollution. However, the increased SO42- and NO3- during summer at SL were mainly caused by LTP, photochemical processes in daytime hours, and heterogeneous processes in nighttime hours.