The Relationship of Particulate Matter and Visibility under Different Meteorological Conditions in Seoul, South Korea

Visibility is defined as the greatest distance at which an observer can distinguish a black object. In metropolitan areas, visibility can also be a criterion of which people can assess their ambient air quality. Meanwhile, there has been a growing concern of fine particulate matter (PM_2.5) pollution in Seoul, South Korea. Since PM_2.5 is one of the main causes of visibility impairment, citizens in Seoul likely associate poor visibility with high PM_2.5 pollution level. However, visibility can also be affected by other meteorological conditions, which arouses the need for a better understanding of the relationship between PM_2.5 and visibility in Seoul. In this study, daily mean of PM₁₀ and PM_2.5 mass concentration data from 2006 to 2018 were collected from the Korean Ministry of Environment and the Seoul Research Institute of Public Health and Environment. Meteorological data were collected from automatic synoptic observation system (ASOS) in central Seoul. For this over-ten-year study period, relative humidity and both PM₁₀ and PM_2.5 mass concentrations decreased, while visibility showed an increasing trend. To determine which factors affect visibility impairment, we examined the correlations between visibility and various factors such as PM₁₀, PM_2.5, and meteorological conditions (relative humidity, temperature, wind speed, solar irradiance, fog occurrence etc.) for the whole research period. Since meteorological conditions in South Korea have distinct differences in each season, we then examined the seasonal pattern of PM₁₀, PM_2.5, and meteorological conditions. By comparing the correlation of various meteorological conditions with PM_2.5 in each season, we demonstrate the seasonal differences of the influence of PM_2.5 on visibility. This seasonal difference in the meteorological conditions may also have an impact on secondary aerosol formation. Therefore, we analyzed the response of PM_2.5 and fine mode fraction (FMF) under different meteorological conditions.