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Factors controlling surface ozone in the Seoul Metropolitan Area During the Korus AQ campaign
Citation:
Kim, H., J. Gil, J. Jung, A. Whitehill, J. Szykman, G. Lee, D. Kim, S. Cho, J. Ahn, J. Hong, AND M. Park. Factors controlling surface ozone in the Seoul Metropolitan Area During the Korus AQ campaign. Elementa: Science of the Anthropocene. University of California Press (UC Press), Oakland, CA, 8:46, (2020). https://doi.org/10.1525/elementa.444
Impact/Purpose:
1) This study addresses air quality issues in Seoul, Korea. In particular, it discusses persistent summertime ozone regulatory exceedances. The work is a summary of results from the Olympic Park ground site during the KORUS-AQ field study in Seoul, South Korea in 2016 and addresses the VOC and NOx sensitivity of ozone production in the region. These findings can be used to help form policy to reduce ozone exceedances in the Republic of Korea.
Description:
To understand the characteristics of air quality in the Seoul Metropolitan Area (SMA), intensive measurements were conducted under the KORea-United States Air Quality (KORUS-AQ) campaign. Trace gases such as O3, NOx, NOy, SO2, CO, and VOC (volatile organic compounds), photochemical byproducts such as H2O2 and HCHO, aerosol species, and meteorological variables including boundary layer height were simultaneously measured at the Olympic Park in Seoul from 10th May to 12th June, 2016. During the entire measurement period, high-O3 episodes that exceeded the hourly maximum of 90 ppbv occurred on 14 days under four distinct synoptic meteorological conditions. Furthermore, local circulation such as land-sea breeze and diurnal evolution of the boundary layer played a critical role in determining the concentrations of precursor gases, including NOx and VOC as well as O3. During such episodes, the nighttime NOx and VOC and daytime UV levels were significantly higher than in the non-episode days. The overall precursor levels and photochemical activity was represented fairly well by variation in the HCHO, which peaked in the morning during the episodes. This experiment revealed that toluene was the most abundant VOCs in Seoul and its concentration was greatly increased with NOx due to the large local influence under stagnant conditions. When O3 was highly elevated concurrently with PM2.5 under dominant westerlies, NOx and VOCs were relatively lower than in other episodes, and the OH reactivity of CO surpassed that of any other VOC species. In addition, the O3 production efficiency was the highest due to low NOx with the highest NOz/NOy ratio among the four episodes. In this episode, the nighttime concentration of O3 remained as high as 40~50 ppbv due to the minimum level of NOx titration. Overall, the SMA is at NOx-saturated and VOC-limited conditions, which was diagnosed by indicator species and VOC/NOx ratios. The model simulation demonstrated that the daily maximum O3 was reduced proportionally with reduction in VOCs but increased upon NOx reduction to non-episode level. Considering that nitrate is the main contributor to PM2.5, our results suggest that caution needs to be exerted, when establishing NOx reduction policies to improve air quality.
URLs/Downloads:
DOI: Factors controlling surface ozone in the Seoul Metropolitan Area During the Korus AQ campaign
elementa.444