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

PM10 and PM2.5 were collected during spring at East (“Gangneung”) and West (“Taean”) coastal sites of the Korean peninsula to investigate chemical characteristics and likely formation routes of their water-soluble inorganic species. The Gangneung site is inland, about 4.5–5.0 km from the East Sea; the Taean site is about 200 m from the coastline and about 400 km from eastern China. The total water-soluble ionic species contributions to PM10 and PM2.5 were respectively 28.8 and 37.4% at the Gangneung site and 46.8 and 53.1% at the Taean site. Concentrations of SO42−, NH4+, and NO3− in both PM10 and PM2.5 were found to be two times higher at the Taean site than at the Gangneung site. The potential source contribution function (PSCF) maps indicate that the enhancement of PM10 and its secondary aerosol species concentrations at two sites were primarily the result of atmospheric processing during long-range transport from the polluted regions of eastern China. Also upwind sources (“the capital region of Korea”) and local emissions influenced the concentration levels of secondary inorganic species at Gangneung.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.