Abstract
Abstract. 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 µg m−3 yr−1) and increase in O3 (+0.88 ppb yr−1) in Seoul were largely contributed by the meteorology-related trends (−0.94 µg m−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.
Highlights
Over the past few decades, rapid urbanization, population and economic growth, and increase in energy consumption have exacerbated air pollution in the developing countries of South and East Asia (Sun et al, 2016; Liu et al, 2017; Shi et al, 2018)
The act includes the introduction of the emission cap-and-trade system and strengthening volatile organic compounds (VOCs) management, most of the budget has been allocated for the expansion of diesel particulate filter (DPF) and diesel oxidation catalyst (DOC) usage for old diesel vehicles, which was considered to be effective for reduction of nitrogen oxides (NOx) and primary particulate matter (PM) emissions (Kim and Lee, 2018)
Based on the statistical approach to the long-term air pollutant measurement data from the urban air quality monitoring sites in Seoul, the present study revealed the important role of synoptic weather conditions on the episodic air pollution events and the meteorological effects on the long-term air pollution trends
Summary
Over the past few decades, rapid urbanization, population and economic growth, and increase in energy consumption have exacerbated air pollution in the developing countries of South and East Asia (Sun et al, 2016; Liu et al, 2017; Shi et al, 2018). Despite the efforts to reduce the primary pollutants and secondary precursors, East Asian countries still suffer from frequent severe haze pollution (Huang et al, 2014) and experience continuous increasing of ozone (O3) levels (Seo et al, 2014; Sun et al, 2016) Such a discrepancy between the past reduction of emissions and the current continuous air pollution can be minimized by considering effects of meteorological conditions on the air quality. Considering that the air quality of Seoul is largely affected by the transport of regional air pollutants and the synoptic meteorological conditions (Seo et al, 2017), the efficiency of the current emission control policy should be evaluated after understanding and quantitative isolating the meteorological effects on the long-term measurement data. The annual estimated emissions of sulfur oxides (SOx), NOx, CO, volatile organic compounds (VOCs), and PM10 in Seoul from the Clean Air Policy Support System (CAPSS) inventory (Lee et al, 2011; NIER, 2018); the national gross domestic product (GDP) growth (IMF, 2017); and the annual consumptions of the final energy, petroleum, and anthracite in Seoul (KEEI, 2016) were used in this study
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