Physicochemical and temporal characteristics of individual atmospheric aerosol particles in urban Seoul during KORUS-AQ campaign: insights from single-particle analysis

Single-particle analysis was conducted to characterize atmospheric aerosol particles collected at Olympic Park in Seoul, South Korea, as a part of the Korea-United States Air Quality (KORUS-AQ) campaign which was carried out during May-June 2016. The KORUS-AQ campaign aimed to understand the temporal and spatial characteristics of atmospheric pollution on the Korean Peninsula through an international cooperative field study. A total of 8004 individual particles from 52 samples collected between 23 May-5 June 2016 were investigated using a quantitative electron probe X-ray microanalysis (low- Z particle EPMA), resulting in the identification of seven major particle types. These included genuine and reacted mineral dust, sea-spray aerosols, secondary aerosol particles, heavy-metal-containing particles, combustion particles, Fe-rich particles, and others (particles of biogenic and humic-like substances - HULIS). Distinctly different relative abundances of individual particle types were observed during five characteristic atmospheric situations, namely (a) a mild haze event influenced by local emissions and air mass stagnation; (b) a typical haze event affected by northwestern air masses with a high proportion of sulfate-containing particles; (c) a haze event with a combined influence of northwestern air masses and local emissions; (d) a clean period with low particulate matter concentrations and a blocking pattern; and (e) an event with an enhanced level of heavy-metal-containing particles, with Zn, Mn, Ba, Cu, and Pb being the major species identified. Zn-containing particles were mostly released from local sources such as vehicle exhausts and waste incinerations, while Mn-, Ba-, and Cu-containing particles were attributed to metal alloy plants or mining. The results suggest that the morphology and chemical compositions of atmospheric aerosol particles in urban areas vary depending on their size, sources, and reaction or aging status and are affected by both local emissions and long-range air masses.