Characteristics of water-soluble inorganic species in PM10 and PM2.5 at two coastal sites during spring in Korea

SO42− events, defined by PM10SO42− concentrations exceeding the average by one standard deviation, were identified at the two sites - six at Gangneung and four at Taean - to investigate possible mechanisms for the formation of SO42− and NO3−. High SO42− and high NO3− at the Gangneung site were strongly associated with either high RH (89-94%) and low wind speed or high O3 (62-103 ppb), suggesting that either gas-phase oxidation or aqueous phase oxidation played a critical role in the enhanced SO42− production. On the other hand, at the Taean site the association was with both high RH (76-92%) and high O3 (53-79 ppb), indicating that these conditions trigger aqueous-phase and gas-phase reactions to produce secondary SO42− and NO3− particles. Also long-range transport of air masses could be one possible factor for enhanced SO42− and NO3− concentrations during the events at the two coastal sites, as evidenced by PSCF maps.