Effects of meteorology and emissions on urban air quality: A quantitative statistical approach to long-term records (1999-2016) in Seoul, South Korea

Together with emissions of air pollutants and precursors, meteorological conditions play important roles in local air quality through accumulation or ventilation, regional transport, and atmospheric chemistry. In this study, we extensively investigated multi-timescale meteorological effects on the urban air pollution using the long-term measurements data of PM₁₀, SO₂, NO₂, CO, and O₃ and meteorological variables over the period of 1999-2016 in Seoul, South Korea. The long-term air quality data were decomposed into trend-free short-term components and long-term trends by the Kolmogorov-Zurbenko filter, and the effects of meteorology and emissions were quantitatively isolated using a multiple linear regression with meteorological variables. In terms of short-term variability, intercorrelations among the pollutants and meteorological variables and composite analysis of synoptic meteorological fields exhibited that the warm and stagnant conditions in the migratory high-pressure system are related to the high PM₁₀ and primary pollutant, while the strong irradiance and low NO₂ by high winds at the rear of a cyclone are related to the high O₃. In terms of long-term trends, decrease in PM₁₀ (-1:75 μgm^-3 yr^-1) and increase in O₃ (+0:88 ppb yr^-1) in Seoul were largely contributed by the meteorology-related trends (-0:94 μgm^-3 yr^-1 for PM₁₀ and +0:47 ppb yr^-1 for O₃), which were attributable to the subregional-scale wind speed increase. Comparisons with estimated local emissions and socioeconomic indices like gross domestic product (GDP) growth and fuel consumptions indicate probable influences of the 2008 global economic recession as well as the enforced regulations from the mid-2000s on the emission-related trends of PM₁₀ and other primary pollutants. Change rates of local emissions and the transport term of long-term components calculated by the tracer continuity equation revealed a decrease in contributions of local emissions to the primary pollutants including PM₁₀ and an increase in contributions of local secondary productions to O₃. The present results not only reveal an important role of synoptic meteorological conditions on the episodic air pollution events but also give insights into the practical effects of environmental policies and regulations on the long-term air pollution trends. As a complementary approach to the chemical transport modeling, this study will provide a scientific background for developing and improving effective air quality management strategy in Seoul and its metropolitan area.