When and why PM 2.5 is high in Seoul, South Korea: Interpreting long-term (2015-2021) ground observations using machine learning and a chemical transport model.

Autor: Lee HM; Department of Environmental Science and Engineering, Ewha Womans University, Seoul, South Korea. Electronic address: hyungmin.lee@ewha.ac.kr., Kim NK; Department of Environmental Science and Engineering, Ewha Womans University, Seoul, South Korea., Ahn J; Air Quality Research Division, National Institute of Environmental Research, Incheon, South Korea., Park SM; Air Quality Research Division, National Institute of Environmental Research, Incheon, South Korea., Lee JY; Department of Environmental Science and Engineering, Ewha Womans University, Seoul, South Korea., Kim YP; Department of Chemical Engineering and Materials Science, Ewha Womans University, Seoul, South Korea.
Jazyk: angličtina
Zdroj: The Science of the total environment [Sci Total Environ] 2024 Apr 10; Vol. 920, pp. 170822. Date of Electronic Publication: 2024 Feb 15.
DOI: 10.1016/j.scitotenv.2024.170822
Abstrakt: Seoul has high PM 2.5 concentrations and has not attained the national annual average standard so far. To understand the reasons, we analyzed long-term (2015-2021) hourly observations of aerosols (PM 2.5 , NO 3 - , NH 4 + , SO 4 2- , OC, and EC) and gases (CO, NO 2 , and SO 2 ) from Seoul and Baekryeong Island, a background site in the upwind region of Seoul. We applied the weather normalization method for meteorological conditions and a 3-dimensional chemical transport model, GEOS-Chem, to identify the effect of policy implementation and aerosol formation mechanisms. The monthly mean PM 2.5 ranges between about 20 μg m -3 (warm season) and about 40 μg m -3 (cold season) at both sites, but the annual decreasing rates were larger at Seoul than at Baengnyeong (-0.7 μg m -3 a -1 vs. -1.8 μg m -3 a -1 ) demonstrating the effectiveness of the local air quality policies including the Special Act on Air Quality in the Seoul Metropolitan Area (SAAQ-SMA) and the seasonal control measures. The weather-normalized monthly mean data shows the highest PM 2.5 concentration in March and the lowest concentration in August throughout the 7 years with NO 3 - accounting for about 40 % of the difference between the two months at both sites. Taking together with the GEOS-Chem model results, which reproduced the elevated NO 3 - in March, we concluded the elevated atmospheric oxidant level increases in HNO 3 (which is not available from the observation) and the still low temperatures in March promote rapid production of NO 3 - . We used O x (≡ O 3  + NO 2 ) from the observation and OH from the GEOS-Chem as a proxy for the atmospheric oxidant level which can be a source of uncertainty. Thus, direct observations of OH and HNO 3 are needed to provide convincing evidence. This study shows that reducing HNO 3 levels through atmospheric oxidant level control in the cold season can be effective in PM 2.5 mitigation in Seoul.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
(Copyright © 2024 Elsevier B.V. All rights reserved.)
Databáze: MEDLINE
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