TY - JOUR
T1 - When and why PM2.5 is high in Seoul, South Korea
T2 - Interpreting long-term (2015–2021) ground observations using machine learning and a chemical transport model
AU - Lee, Hyung Min
AU - Kim, Na Kyung
AU - Ahn, Joonyoung
AU - Park, Seung Myung
AU - Lee, Ji Yi
AU - Kim, Yong Pyo
N1 - Publisher Copyright:
© 2024 Elsevier B.V.
PY - 2024/4/10
Y1 - 2024/4/10
N2 - Seoul has high PM2.5 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 (PM2.5, NO3−, NH4+, SO42−, OC, and EC) and gases (CO, NO2, and SO2) 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 PM2.5 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 PM2.5 concentration in March and the lowest concentration in August throughout the 7 years with NO3− 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 NO3− in March, we concluded the elevated atmospheric oxidant level increases in HNO3 (which is not available from the observation) and the still low temperatures in March promote rapid production of NO3−. We used Ox (≡ O3 + NO2) 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 HNO3 are needed to provide convincing evidence. This study shows that reducing HNO3 levels through atmospheric oxidant level control in the cold season can be effective in PM2.5 mitigation in Seoul.
AB - Seoul has high PM2.5 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 (PM2.5, NO3−, NH4+, SO42−, OC, and EC) and gases (CO, NO2, and SO2) 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 PM2.5 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 PM2.5 concentration in March and the lowest concentration in August throughout the 7 years with NO3− 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 NO3− in March, we concluded the elevated atmospheric oxidant level increases in HNO3 (which is not available from the observation) and the still low temperatures in March promote rapid production of NO3−. We used Ox (≡ O3 + NO2) 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 HNO3 are needed to provide convincing evidence. This study shows that reducing HNO3 levels through atmospheric oxidant level control in the cold season can be effective in PM2.5 mitigation in Seoul.
KW - GEOS-Chem
KW - Nitrate
KW - Nitric acid
KW - Seasonal variation
KW - Seoul
KW - rmweather
UR - http://www.scopus.com/inward/record.url?scp=85185195747&partnerID=8YFLogxK
U2 - 10.1016/j.scitotenv.2024.170822
DO - 10.1016/j.scitotenv.2024.170822
M3 - Article
C2 - 38365024
AN - SCOPUS:85185195747
SN - 0048-9697
VL - 920
JO - Science of the Total Environment
JF - Science of the Total Environment
M1 - 170822
ER -