Comparison of Particle Number Concentrations Between Small and Large Urban Green Spaces During a PM Pollution Episode in Seoul, South Korea

We analyzed the effect of reducing particulate matter in a forest by comparing concentrations and particle number concentrations (PNCs) between urban and background forest areas with the use of aerodynamic particle sizers. PM was observed at forest and urban sites during the high particulate matter events from 22 to 30 April 2019. Comparing the PM concentrations measured, PM10 and PM2.5 were 61.6 μg/m3 and 36.9 μg/m3, respectively, in the urban site, while PM10 and PM2.5 were 53.9 μg/m3 and 31.8 μg/m3, respectively, in the forest site. Most PNCs at both sites ranged in particle size from less than 0.5 μm (99%). During high-concentration events, the mass concentration of PM10 was not significantly different, but PNCs of the accumulation mode particles (≤0.5 µm) and coarse mode particles (>0.5 µm) were differed between two sites. The re-duction rate of coarse mode particles (>0.5 µm) was lower 20% at large urban green space. A large urban green space showed the high slope value of decrease at the relationship between aerodynamic diameter and PNC at all times. These results indicate that not only mass concentration but PNC could support to understand the PM traits at large urban green space during the PM pollution of episode.