Characterisation of individual aerosol particles collected during a haze episode in Incheon, Korea using the quantitative ED-EPMA technique

A quantitative energy-dispersive electron probe X-ray microanalysis (ED-EPMA), called low-Z particle EPMA, was used to analyse individual aerosol particles collected in Incheon, Korea on 13–18 October 2008 (a typical haze episode occurred from 15 to 18 October). Overall 3600 individual particles in PM2.5-10 and PM1.0-2.5 fractions from 12 aerosol samples collected on haze and non-haze days were analysed. The analysed particles were classified, based on their X-ray spectral data together with their secondary electron images. The major particle types included organic carbon (OC), elemental carbon (EC), sea-salt, mineral dust (such as aluminosilicate, SiO2, CaCO3/CaMgCO3, etc.), (NH4)2SO4/NH4HSO4-containing, K-containing, Fe-rich and fly ash particles. Their relative number abundance results showed that OC particles were significantly increased while sea-salts and mineral dust particles were significantly decreased (especially in PM1.0-2.5 fraction) when haze occurred. For the other particle types (except Fe-rich particles in PM2.5-10 fraction), there were no significant differences in their relative abundances between haze and non-haze samples. On non-haze days, the nitrate-containing reacted sea-salt and mineral dust particles in PM1.0-2.5 fraction significantly outnumbered the sulfate-containing ones, whereas it was the reverse on haze days, implying that on haze days there were special sources or formation mechanisms for fine aerosol particles (≤2.5 μm in aerodynamic diameter). The emission of air pollutants from motor vehicles and stagnant meteorological conditions, such as low wind speed and high relative humidity, might be responsible for the elevated level of OC particles on haze days.