Characterization of PM2.5 Mass in Relation to PM1.0 and PM10 in Megacity Seoul

This study examines the PM_2.5 characteristics in Seoul in relation to those of PM_1.0 and PM₁₀. Samples were typically collected daily on filters and a few hours sampling were conducted during a few haze events (March 2007 to June 2008). Mean mass concentrations of PM_1.0, PM_2.5, and PM₁₀ were 19.7 μg/m³, 26.0 μg/m³, and 48.2 μg/m³, respectively, and PM_2.5 was reasonably correlated with PM_1.0 (γ=0.79) and PM₁₀ (γ=0.52). Three mass group types were mainly distinguished. Group 1 (31%): linear increase of PM_1.0 with PM₁₀ and high OC and NO₃⁻; Group 2 (17%): PM₁₀ considerably higher than PM_1.0 and high Ca²⁺ and SO₄²⁻; Group 3 (52%): PM_1.0 relatively more enhanced than PM₁₀ and highest carbonaceous fraction against mass. The fine mode fraction was lowest (highest) in Group 2 (Group 3). Haze and dust episodes relating to Chinese outflows were mostly evident in Groups 1 and 2, respectively; average PM_2.5 concentrations were visibly higher than in Group 3. Non-Negative Matrix Factorization analysis demonstrated that traffic-related urban primary (28%) and coal-fired industry (27%) emissions equally contributed to the PM_2.5 mass, followed by aged urban secondary (19%), soil mineral (16%), and biomass combustion (10%) sources. Seasonal variations were apparent in air mass trajectories. Urban primary and coal-fired industry factors were predominant in Group 3 under stagnant conditions in the warm season and under a strong northerly wind in the cold season, respectively. However, contributions of the other three factors were higher in Groups 1 and 2. This study shows that the PM_2.5 mass in Seoul is largely dependent on high concentration episodes occurring mostly in cold seasons. It also shows that local emissions contribute considerably during warm months, while the influence of Chinese outflow predominates during cold months.