LAUSR

Abstract The hourly measurement of inorganic soluble ions in PM10 aerosols was conducted with new in situ air composition measuring equipment (ACME) from March 15 to April 15, 2016, on Kinmen Island. The purposes of this study are to understand the influences of fog on secondary aerosol formation and to determine the impacts of air pollutants on haze formation under different relative humidity conditions. The hourly measurements showed that the mass fraction of sulfate in PM10 increased with increases in the liquid water content of fog and decreases in the gaseous concentrations of SO2. The value of the SO42−/PM10 ratio is also affected by the concentration of SO2 before the fog occurs and the level of the fog. This finding indicates that a humid environment is important for enhancing the heterogeneous reaction of sulfate formation. The nitrate concentrations were related to the ratio of NH4+ to SO42− during fog episodes. The formation of particulate NO3− was associated with ammonium formation under ammonium-rich conditions (NH4+/SO42− > 1.5). The gas-phase nitrate was usually observed under ammonium-poor conditions. During periods of high particle pollution, the air mass was from near the ground surface in the mainland coastal areas and transported more pollution to Kinmen. The concentrations of NO2− were higher during periods of high particle pollution, which means that the secondary aerosol formation in the nearby areas also strongly affected the air quality degradation. The short-term and rapid change in the north-south wind system not only brings water vapor from the south but also delivers accumulated pollutants via the transport of northern pollution at low wind speeds.