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Meteorological and Chemical Factors Controlling Ozone Formation in Seoul during MAPS-Seoul 2015

Category: MAPS-Seoul Ozone

Volume: 18 | Issue: 9 | Pages: 2274-2286
DOI: 10.4209/aaqr.2017.11.0445
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Heejeong Kim1, Woo-Chul Choi1, Ho-Jun Rhee1, Inseon Suh1, Meehye Lee 1,8, Donald R. Blake2, Saewung Kim3, Jinsang Jung4, Gangwoong Lee5, Deug-Soo Kim6, Seung-Myung Park7, Junyoung Ahn7, Sang Deok Lee7

  • 1 Department of Earth and Environmental Sciences, Korea University, Seoul 02841, Korea
  • 2 Department of Chemistry, University of California, Irvine, CA 92617, USA
  • 3 Department of Earth System Science, University of California, Irvine, CA 92697, USA
  • 4 Center for Gas Analysis, Korea Research Institute of Standards and Science, Daejeon 34113, Korea
  • 5 Department of Environmental Sciences, Hankuk University of Foreign Studies, Yongin 449-791, Korea
  • 6 Department of Environmental Engineering, Kunsan National University, Kunsan 573-701, Korea
  • 7 Department of Climate and Air Quality, National Institute of Environmental Research, Incheon 22689, Korea
  • 8 Green School, Korea University, Seoul 02841, Korea

Highlights

Meteorological condition was a key factor determining the level of NOx and VOCs.
O3 was higher under lower NOx and higher temperature in aged and stagnant air mass.
The contribution of BVOCs to O3 formation was enhanced under stagnant condition.
The formation of O3 was more sensitive to VOCs than NOx during MAPS-Seoul 2015.


Abstract

To understand the chemical mechanisms of controlling factors in ozone (O3) formation in early summer in Seoul, a comprehensive study encompassing measurement and modeling was conducted under the Megacity Air Pollution Study-Seoul (MAPS-Seoul) campaign. From May 18 to June 12, 2015, O3 and peroxyacetyl nitrate (PAN) were measured, along with their precursors, including NOx and volatile organic compounds (VOCs), at the Korea Institute of Science and Technology, located in northeast Seoul. VOCs were sampled in a canister twice a day (at 09:30 and 15:00) and analyzed via gas chromatography. The meteorological conditions and chemical regimes of the air masses were clearly distinguished during the study period. In May, NOx concentrations were higher with more pronounced diurnal cycles of precursors and O3 under constant westerly winds. By contrast, stagnant conditions developed in June, which reduced the inflow of primary emissions from the downtown area but increased the influence from the neighboring forest under high temperatures. As a result, the ratio of O3 to odd oxygen was higher in June, indicating a less efficient removal of O3 by NOx. In the same context, the air mass was chemically more aged with a higher NO2/NOx ratio and enhanced OH reactivity of oxygenated and biogenic VOCs in June. The overall measurement results suggest that O3 formation is slightly more sensitive to VOCs than to NOx in Seoul during this season, when O3 concentrations are the highest of the year.

Keywords

O3 formation NOx VOCs Meteorological condition MAPS-Seoul

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