AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Chemical Composition, Sources and Formation Process of Submicron Aerosols in Seoul Metropolitan Area during Summer: Comparison to Winter
HWAJIN KIM, Qi Zhang, Korea Institute of Science and Technology
Abstract Number: 387 Working Group: Urban Aerosols
Abstract To investigate the seasonal characteristics of submicron aerosol (PM1) in urban Korea, characteristics of PM1 were investigated using an HR-ToF-AMS in the Seoul Metropolitan Area (SMA) during summer. Also by applying positive matrix factorization (PMF), organic aerosol (OA) sources were investigated and the results were compared to the one in winter.
In summer, the average concentration of PM1 was 19.1 μg m-3, which was composed of 49% organics, 28% SO4, 7% NO3, and 9% NH4. And eight distinct sources of OA were identified: hydrocarbon like OA (HOA), cooking OA (COA), nitrate OA (NO3-OA), sulfate OA (SO4-OA), nitrogen enriched OA (NOA) and three different levels of oxidized OA (OOA1, OOA2, OOA3).
Compared to winter, the average PM1 concentration was lower during summer (19.1 vs 27.5 µg m−3), the mass fraction of SO4 was higher (28 vs. 10 %) but that of NO3 was lower (7 vs 24 %). Together with lower SO2 in summer (4.3 vs 6.9 ppb), higher SO4 concentration (5.4 vs 2.9 µg m−3) indicate the more efficient conversion of SO2 to SO4 under stronger solar radiation (0.95 vs 0.66 MJ/m2) or more regional transport of sulfate. Furthermore, PMF analysis indicate that about 20% of SO4 during summer is in organic combined. In terms of OA, OA was more oxidized (O/C ratios; 0.46 vs 0.37) and more different types of SOA sources (6 vs 2) were observed, composing higher SOA fraction than the one in winter (80 vs 41%). One reason for this is the intensive photochemical formation occurred in summer showing the better (r=0.65 vs 0.47) and higher daytime OOA/Ox ratios (0.17 vs 0.12). Also the impact of POA was less in summer. These results indicate that air quality in SMA reflect the differences between the two seasons in meteorology, emissions sources and formation processes of air pollutants.