Analysis of O3 and dust concentrations measured at west Cheong-ju city in Korea during the KORUS-AQ 2016

The Korea-United States Air Quality (KORUS-AQ) joint measurements primarily focused on the western region of South Korea during May and June 2016. This study thoroughly analyzes ground-level O₃ and dust concentrations at a rural research site in west Cheong-ju city, located 125 km south of Seoul. Over the 45-day observation period, 33 days exhibited episodes of high O₃ levels exceeding 81 ppb. On 8 days, peak hourly O₃ concentrations ranged between 120 ppb and 137 ppb. High O₃ levels persisted for 5 to 14 h on 28 days, with 13 days experiencing concentrations exceeding 10 h daily. Simultaneously, there were 16 episodes of elevated dust levels, with hourly PM₁₀ exceeding 81 µg m^-3, among which 5 days recorded PM₁₀ values surpassing 100 µg m^-3. During the campaign, 6 days witnessed high hourly PM_2.5 values ranging from 51 to 74 µg m^-3. On 7 May, a moderate dust fall occurred due to a sand storm originating from Mongolia and northern China, with the highest hourly TSP value reaching 345 µg m^-3. The PM₁₀ concentration during this event was 244 µg m^-3, while PM_2.5 levels were relatively lower at 41 µg m^-3. In comparison, on 2 May, elevated concentrations resulting from pine tree pollen release were observed, with TSP, PM₁₀, and PM_2.5 values reaching 357 µg m^-3, 106 µg m^-3, and 23 µg m^-3, respectively. Detailed and meticulous analyses involving air-parcel trajectory and satellite imagery were conducted to ascertain the causes of long-range transport of air pollution (LRTAP). The increase in O₃ due to LRTAP intensifies the atmosphere’s oxidizing capacity, possibly contributing to the formation of secondary aerosols in PM_2.5. The findings indicate that local and regional emissions from China contributed to the air pollution episodes observed during the study period.