Characterization of Aerosols Collected During KORUS-AQ (Korea US Air Quality) Sampling Period in Olympic park, Seoul, using Low-Z particle EPMA and ATR-FTIR Technique

초록

In this work, low-Z particle EPMA (electron probe X-ray microanalysis) and ATR-FTIR (attenuated total reflectance Fourier transform infrared) spectroscopy were applied to characterize aerosol samples collected during KORUS-AQ sampling period (5/23 ~ 6/5, 2016) at Olympic park, Seoul, Korea. PM2.5-10 and PM1-2.5 samples were collected on Ag and Al foil using 3-stage cascade impactor (Dekati PM10 sampler) and particles were characterized individually based on secondary electron image and chemical composition using low-Z particle EPMA. PM1-2, PM0.5-1, and PM0.25-0.5 bulk samples were collected on Ag foils using 7-stage May impactor and functional groups were investigated by ATR-FTIR technique. Overlapping peaks from ATR-FTIR spectra were separated to compare relative tendency of each functional group with the help of a homemade curve fitting tool. As a result of low-Z EPMA analysis, major species consist of mineral dust (aluminosilicate, Ca/CaMgCO3, SiO2, TiO2), reacted mineral dust, organics (organic carbon, (NH4)2SO4/NH4HSO4-containing, K-containing, biogenic), reacted sea salts, Fe-rich, heavy metal containing, soot, tar ball, and fly ash particles. Proportion of organic particles in PM1-2.5 fraction significantly increased from 5/25 until 5/28 AM, which might be due to a haze event (5/25 ~ 5/31, high PM concentration). Also, noticeable amounts of heavy metal containing particles such as Pb, Cu, Zn, Mn, Cr, V, Sn, Zr, La, As, Sb, Ni, Cd, and Co were observed in both PM1-2.5 and PM2.5-10 fractions (around 3.4% out of 278 particles). From the results of ATR-FTIR, PM1-2, PM0.5-1, and PM0.25-0.5 samples were mainly composed of NH4+, SO42-, NO3-, and organics. During the haze events, average ratio of NO3-/SO42- was about 17.5, 12.7, and 1.7 times higher than non-haze days in PM1-2, PM0.5-1 and PM0.25-0.5 fractions, respectively. Decrease of NO3-/SO42- ratio was significant from AM to PM in most samples and relatively higher in submicron fractions.