09 Dec 2022
09 Dec 2022
Status: this preprint is open for discussion.

Why is ozone in South Korea and the Seoul Metropolitan Area so high and increasing?

Nadia Kathryn Colombi1, Daniel J. Jacob1, Laura Hyesung Yang2, Shixian Zhai2, Viral Shah3,4, Stuart K. Grange5, Robert M. Yantosca2, Soontae Kim6, and Hong Liao7 Nadia Kathryn Colombi et al.
  • 1Harvard University, Department of Earth and Planetary Science, Cambridge, MA 02138, USA
  • 2Harvard University, John A. Paulson School of Engineering and Applied Sciences, Cambridge, MA 02138, USA
  • 3NASA Global Modeling and Assimilation Office, Goddard Space Flight Center, Greenbelt, MD 20771, USA
  • 4Science Systems and Applications, Inc., Lanham, MD 20706, USA
  • 5Empa, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129 8600 Dübendorf, Switzerland
  • 6Ajou University, Department of Environmental and Safety Engineering, Suwon, Gyeonggi 16499, Republic of Korea
  • 7Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control, Jiangsu Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, School of Environmental Science and Engineering, Nanjing University of Information Science & Technology, Nanjing 210044, China

Abstract. Surface ozone pollution in South Korea has increased over the past two decades, despite efforts to decrease emissions, and is pervasively in exceedance of the maximum daily 8-hr average (MDA8) standard of 60 ppb. Here, we investigate the 2015–2019 trends in surface ozone and NO2 concentrations over South Korea and the Seoul Metropolitan Area (SMA), focusing on the 90th percentile MDA8 ozone as an air quality metric. We use a random forest algorithm to remove the effect of meteorological variability on the 2015–2019 trends and find an emission-driven ozone increase of up to 1.5 ppb a-1 in April–May while NO2 decreases by 22 %. GEOS-Chem model simulations including recent chemical updates can successfully simulate surface ozone over South Korea and China as well as the very high free tropospheric ozone observed above 2 km altitude (mean 75 ppb in May–June), and can reproduce the observed 2015–2019 emission-driven ozone trend over the SMA including its seasonality. Further investigation of the model trend for May, when meteorology-corrected ozone and its increase are the highest, reveals that a decrease in South Korea NOx emissions is the main driver for the SMA ozone increase. Although this result implies that decreasing volatile organic compound (VOC) emissions is necessary to decrease ozone, we find that SMA ozone would still remain above 80 ppb even if all anthropogenic emissions in South Korea were shut off. China contributes only 8 ppb to this elevated South Korea background and ship emissions contribute only a few ppb. Zeroing out all anthropogenic emissions in East Asia in the model indicates a remarkably high external background of 56 ppb, consistent with the high concentrations observed in the free troposphere, implying that the air quality standard in South Korea is not practically achievable unless this background external to East Asia can be decreased.

Nadia Kathryn Colombi et al.

Status: open (until 06 Feb 2023)

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  • RC1: 'Comment on egusphere-2022-1366', Anonymous Referee #1, 29 Dec 2022 reply

Nadia Kathryn Colombi et al.

Nadia Kathryn Colombi et al.


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Short summary
Surface ozone, detrimental to human and ecosystem health, is very high and increasing in South Korea. Using a global model of the atmosphere, we found that emissions from South Korea and China contribute equally to the high ozone observed. We found that in the absence of all anthropogenic emissions over East Asia, ozone is still very high, implying that the air quality standard in South Korea is not practically achievable unless this background external to East Asia can be decreased.