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Abstract
Author(s): Kim, H; Choi, WC; Rhee, HJ; Suh, I; Lee, M; Blake, DR; Kim, S; Jung, J; Lee, G; Kim, DS; Park, SM; Ahn, J; Lee, SD | 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.
Highlights
The exposure to high concentrations of O3 has adverse effects on human health (Thurston and Ito, 2001), forest ecosystems, agriculture (Fuhrer, 2003; Karnosky et al, 2005), and global climate (Hogrefe et al, 2004; Hubbell et al, 2005)
In Korea, O3 concentration is generally highest during May–June, which is before the summer monsoon season
The present study demonstrates that, in the Seoul Metropolitan Area (SMA), the levels of nitrogen oxides (NOx) and volatile organic compounds (VOCs) were greatly affected by meteorological conditions
Summary
The exposure to high concentrations of O3 has adverse effects on human health (Thurston and Ito, 2001), forest ecosystems, agriculture (Fuhrer, 2003; Karnosky et al, 2005), and global climate (Hogrefe et al, 2004; Hubbell et al, 2005). Various plans implemented with the view of controlling O3 and reducing the emission of its precursors, In Seoul, the capital of South Korea, the O3 concentration increased during the 1990s and seemed to slightly decrease in the early 2000s, when public attention rapidly turned to PM10 owing to record-high values of Asian dust being recorded in 2002 (KMOE, 2016). NO2 concentrations have not decreased proportionally, leading to a higher NO2/NOx ratio (Han et al, 2013). This is consistent with the increased O3 observed in most urban areas in Korea (e.g., An et al, 2015). NOx reduction was likely more effective due to the use of low-emission vehicles and natural gas than to VOC emission control because of illicit emissions from small facilities (Lee et al, 2015; Kim et al, 2017)
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