Mass Size Distributions of Water-soluble Organic and Inorganic Species in Ambient Air at an Urban Site in Gwangju during November 2019

Mass size distributions of water-soluble organic and inorganic species in ambient aerosol particles were examined at an urban site in Gwangju for period from November 2 through 26, 2019. During the study period, particulate matter (PM) and NO3- exhibited mostly bi-modal size distributions with particle sizes at 0.32 and 3.1 mu m, while water-soluble organic carbon, SO42-, NH4+ and K+ had typically uni-modal size distribution at a diameter of 0.32 or 0.55 mu m. Size distributions of NO3- observed in PM suggest that NO3- particles were formed through homogeneous reactions of NO2 in condensational mode and through heterogeneous reactions of gaseous nitric acid on surface of CaCO3 particles in coarse mode, which is clearly associated with increase in coarse mode PM concentration. On day (November 2) when the highest PM2.5 concentration (35.9 mu g/m(3)) occurred, PM showed strong bi-modal size distribution peaking at 0.32 and 3.1 mu m due to stable air conditions, locally produced pollution, and impact of Asian dust occurred on preceding day. On the other hand, on November 18 when Asian dust occurred, PM exhibited also bi-modal size distribution peaking at 0.32 and 3.1 mu m, but with a predominant coarse mode due to increased concentration of Ca2+. Furthermore, Na+ and Cl-showed strong peaks in the coarse mode, due to possibly influx of sea-salt particles during transport of air masses from China. Results from size distributions of PM and its water-soluble chemical species would help to understand their emission sources and formation processes.