From Home and Abroad─Atmospheric Age-Resolved Modeling Reveals the Origin and Evolution of Photochemical Ozone in South Korea

An age-resolved modeling framework is developed to investigate the domestic and international emissions to surface ozone (O3) concentrations in South Korea in the summer and early fall of 2020. The analyses not only reveal the source-origin of O3 but also lead to a quantitative understanding of the relevant formation and transport time scales associated with different types of high O3 events. Frontal systems create unstable synoptic weather patterns that can lead to quick fluctuations in the importance of international or domestic emissions on high O3 days. In June, high domestic O3 days occur when a relatively stationary weather front is situated over the Korea Strait. On these days, moderate accumulation of domestic O3 occurs, reaching peak hourly concentrations of 40-45 ppb and an average atmospheric age of 20–30 h. Conversely, in August, high domestic O3 occurs due to a week-long high-pressure system. This results in a greater accumulation of aged domestic O3, with hourly concentrations ranging from 80–100 ppb and an average atmospheric age of 40–50 h. O3 originating from eastern and northeastern China also contributes significantly, with monthly averages ranging from 5–15 ppb. In June, hourly O3 from China reaches as high as 40 ppb and an average atmospheric age of less than 60 h, compared to 80–90 h on typical low O3 days. More importantly, the strong westerly winds on the rear of several strong typhoons passing through the Korean Peninsula in August and September transport up to 50 ppb of hourly O3 from China in less than a day.