Physical and chemical mechanisms of the daily-to-seasonal variation of PM10 in Korea.

Affiliation

School of Earth and Environmental Sciences, Seoul National University, Seoul 08826, Republic of Korea. Electronic address: [Email]

Abstract

In this study, the CSEOF technique is used to investigate the physical and chemical mechanisms associated with the weekly PM10 variation in South Korea. For this end, 9 years of hourly measurements of PM10 in South Korea is used together with other gaseous contaminants (NO2, SO2, CO and O3) and traffic counts at the toll gates. The diurnal variation of PM10 concentrations indicates a significant correlation with human activities; higher concentrations in densely populated areas with a large volume of traffics and vice versa. In particular, the diurnal cycles of PM10, NO2 and CO show bimodal structures with maxima corresponding to the morning and evening rush hours. While NO2 and CO maxima are observed at ~9 AM, with some delay from the traffic maximum, PM10 peak is observed ~11 AM, indicating roughly 2 h of conversion process from gaseous pollutants to particulate matter. After the sunset, gas-to-particle conversion efficiency is significantly reduced and PM10 concentration begins to increase slowly. SO2 exhibits a slightly different feature, showing diurnal variation with a single peak at 11 AM and relatively minor contribution to the diurnal variation of PM10. O3 participates in the photochemical reactions of the gaseous pollutants, providing OH radical as an oxidant. Physical factors (e.g. boundary layer height, 10 m wind gust, wind convergence) affecting horizontal and vertical mixing of polluted air are responsible for dispersion of accumulated PM10 in the afternoon. As a result, strong morning-evening asymmetry is seen in the diurnal variation of PM10 concentrations. Also, notable seasonal dependency is observed in the concentrations of PM10 and the gaseous contaminants due to the seasonal variation of emission and the physical factors.

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