Research article Vertical stratification of volatile organic compounds and their photochemical product formation potential in an industrial urban area Thi-Dieu-Hien Vo a , Chitsan Lin a, * , Chien-Erh Weng b , Chung-Shin Yuan c , Chia-Wei Lee d , Chung-Hsuang Hung d , Xuan-Thanh Bui e , Kuo-Cheng Lo f , Jun-Xian Lin a a Institute of Marine Science and Technology, National Kaohsiung University of Science and Technology, Kaohsiung 81157, Taiwan b Department of Electronic Communication Engineering, National Kaohsiung University of Science and Technology, Kaohsiung 81157, Taiwan c Institute of Environmental Engineering, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan d Department of Safety, Health and Environmental Engineering, National Kaohsiung University of Science and Technology, Kaohsiung 82445, Taiwan e Faculty of Environment and Natural Resources, University of Technology, Vietnam National University - Ho Chi Minh City, Viet Nam f Department of Military Meteorology, Air Force Institute of Technology, Kaohsiung 82047, Taiwan article info Article history: Received 11 October 2017 Received in revised form 21 March 2018 Accepted 22 March 2018 Keywords: Vertical VOC stratification Ozone formation potential (OFP) Secondary organic aerosol formation potential (SOAFP) Inversion layer Unmanned aerial vehicle (UAV) abstract High emissions of volatile organic compounds (VOCs) from the petrochemical industry and vehicle exhaust may contribute to high ozone formation potential (OFP) and secondary organic aerosol forma- tion potential (SOAFP). In this study, the vertical profiles of VOCs were created for the southern Taiwan industrial city of Kaohsiung. Vertical air samples were collected up to 1000 m using an unmanned aerial vehicle (UAV). In Renwu District, VOC distribution was affected by the inversion layer up to 200 m height. Total VOCs (36e327 ppbv), OFP (66e831 ppbv) and SOAFP (0.12e5.55 ppbv) stratified by height were the highest values at 300 m. The VOCs originated from both local and long-distance transport sources. These findings can be integrated into Kaohsiung's future air quality improvement plans and serve as a reference for other industrialized areas worldwide. © 2018 Elsevier Ltd. All rights reserved. 1. Introduction Kaohsiung city, the most industrialized area in southern Taiwan, has suffered greatly from air pollution in the past decades. For 131 days a year (36%), the air quality index (AQI) values fell into un- healthy category (101e 150) in Kaohsiung, the highest rate in Taiwan (TAQMN, 2018). Due to the rapid development of petro- chemical industry, the concentrations of volatile organic com- pounds (VOCs) in the ambient air have always been a great concern. In Kaohsiung the petrochemical industry and vehicular exhaust are the two major sources of VOCs (Chen et al., 2012). VOCs, e.g. benzene, toluene, trichloroethene, and styrene, are highly toxic compounds, reported to cause diseases of the respi- ratory, blood, and central nervous systems (WHO, 2000; Kampa and Castanas, 2008; Sahu et al., 2016a). More importantly, VOCs are the precursors of other toxic photochemical products, including ozone and secondary organic aerosols (SOAs) (Sahu et al., 2017a). In the atmosphere, the reactions involving VOCs and NO x under solar radiation lead to the formation of ozone and a variety of carbonyl compounds (Koppmann, 2010; He et al., 2017). The alkyl nitrates and peroxyacetyl nitrate (PAN) are known as secondary pollutants in photochemical smog. In the presence of NO, these secondary pollutants are formed from the oxidation of VOCs by OH radicals, which are formed through the photo-dissociation of ozone under ultraviolet radiation. The lifetime of alkyl nitrates varies from several days to one month depending on their chain length. PAN is thermally unstable so it can decompose into NO x and perox- yethanoyl radicals (Sahu, 2012). More importantly, PAN serves as a carrier for NO x into cleaner areas and also to elevated altitudes, leading to ozone formation worldwide. Surface ozone formation due to high concentrations of ozone precursors is a serious air pollution problem in industrialized areas (Sahu et al., 2016b). Regulatory programs and state implementation plans have been conducted in many countries (e.g. the United States, Europe, Taiwan, etc.) in past decades to reduce exposure to ground-level ozone. However, many areas continue to exceed the * Corresponding author. E-mail address: ctlin@webmail.nkmu.edu.tw (C. Lin). Contents lists available at ScienceDirect Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman https://doi.org/10.1016/j.jenvman.2018.03.101 0301-4797/© 2018 Elsevier Ltd. All rights reserved. Journal of Environmental Management 217 (2018) 327e336