Seasonal Characteristics of PM2.5 Water Content at Seoul and Gosan, Korea

Water content of PM2.5 (particles in the atmosphere with a diameter of less than or equal to a nominal 2.5 mu m) was estimated by using a gas/aerosol equilibrium model, SCAPE2, for the particles collected at Seoul and Gosan, Korea. From measured and analyzed characteristics of the particles, the largest difference between Seoul and Gosan is the proportions of total ammonia (t-NH3= gas phase NH3+ particle phase NH4 +), total nitric acid (t-HNO3= gas phase HNO3+particle phase NO3-) and sulfuric acid (H2SO4). Even though both sites have sufficient t-NH3 to neutralize acidic species such as H2SO4, t-HNO3, and t-HCl (total chloric acid=gas phase HCl+ particle phase Cl-), equivalent fraction of t-NH3 and t-HNO3 are higher at Seoul and H2SO4 is higher at Gosan. Based on the modeling result, it is identified that the PM2.5 at Seoul is more hygroscopic than Gosan if the meteorological conditions are the same. To reduce water content of PM2.5, and thus, mass concentration, control measures for ammonia and nitrate reduction are needed for Seoul, and inter-governmental cooperation is required for Gosan.