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The Controlling Factors of Photochemical Ozone Production in Seoul, South Korea

Category: MAPS-Seoul OH Reactivity

Volume: 18 | Issue: 9 | Pages: 2253-2261
DOI: 10.4209/aaqr.2017.11.0452
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Saewung Kim 1, Daun Jeong1, Dianne Sanchez1, Mark Wang1, Roger Seco1, Donald Blake2, Simone Meinardi2, Barbara Barletta2, Stacey Hughes2, Jinsang Jung3, Deugsoo Kim4, Gangwoong Lee5, Meehye Lee6, Joonyoung Ahn7, Sang-Deok Lee8, Gangnam Cho7, Min-Young Sung7, Yong-Hwan Lee7, Rokjin Park9

  • 1 Department of Earth System Science, University of California, Irvine, CA 92697, USA
  • 2 Department of Chemistry, University of California, Irvine, CA 92617, USA
  • 3 The Division of Metrology for Quality of Life, Korea Research Institute of Standards and Science, Daejeon 34113, Korea
  • 4 Department of Environmental Engineering, Kunsan National University, Kunsan 573-701, Korea
  • 5 Department of Environmental Sciences, Hankuk University of Foreign Studies, Yongin 449-791, Korea
  • 6 Department of Earth and Environmental Sciences, Korea University, Seoul 02841, Korea
  • 7 Department of Climate and Air Quality, National Institute of Environmental Research, Incheon 22689, Korea
  • 8 College of Forest and Environmental Sciences, Kangwon National University, Chuncheon 24341, Korea
  • 9 School of Earth and Environmental Sciences, Seoul National University, Seoul 08826, Korea

Highlights

Ozone and its precursors observed during the MAPS-Seoul campaign are presented.
Organic peroxy radicals play an important role in ozone production.
OH reactivity analysis highlights VOCs as a limiting factor in ozone production.
A comprehensive observational dataset is the basis for an ozone reduction policy.


Abstract

We present the ambient ozone and relevant observed trace gas dataset in Seoul, South Korea, during the Megacity Air Pollution Studies (MAPS)-Seoul field campaign from May to June of 2015 (MAPS-Seoul 2015). We observed two distinctive periods, one with higher and the other with lower daytime ozone levels despite mostly clear conditions for both periods. The importance of peroxy radical contributions to excess ozone production is illustrated by the substantial differences in the Leighton constant (Φ) for the two periods. Moreover, higher levels of hydroxyl radical (OH) reactivity (s–1) were observed during the high ozone episode compared to the low ozone episode by as much as ~5 s–1. The contributions of nitrogen oxides (NOx) to OH reactivity become less important than those of volatile organic compounds (VOCs) during the high ozone episode, which suggests the NOx saturated ozone production regime. It was also notable that the biogenic VOC isoprene consistently contributed the most to OH reactivity from among the observed VOCs during the afternoon throughout the whole field campaign. Finally, we ran multiple box model scenarios to evaluate the ozone production rates of three different air mixtures: a high ozone mixture, a low ozone mixture, and a simulation of the regional air quality. The results indicate that the total OH reactivity levels and the relative contributions of VOCs to NOx play critical roles in ozone production rates. The simulated air quality mixture results in lower OH reactivity, causing lower ozone production rates than those calculated for the high ozone mixture, which clearly indicates the need for further improvements in the regional model to accurately simulate ozone precursors in the region. The results of this study suggest that a comprehensive trace gas dataset combined with observations of the OH reactivity enables us to properly diagnose the photochemistry behind ozone pollution, leading to effective ozone abatement policies.

Keywords

Ozone Leighton Constant OH reactivity Ozone production regime


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