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Volume 18, issue 19 | Copyright

Special issue: Regional transport and transformation of air pollution in...

Atmos. Chem. Phys., 18, 14417-14432, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 09 Oct 2018

Research article | 09 Oct 2018

Low-level summertime isoprene observed at a forested mountaintop site in southern China: implications for strong regional atmospheric oxidative capacity

Daocheng Gong1, Hao Wang1,2, Shenyang Zhang1, Yu Wang3, Shaw Chen Liu1, Hai Guo3, Min Shao1, Congrong He2,4, Duohong Chen5, Lingyan He6, Lei Zhou1, Lidia Morawska2,4, Yuanhang Zhang7, and Boguang Wang1,2 Daocheng Gong et al.
  • 1Institute for Environmental and Climate Research, Jinan University, Guangzhou 511443, China
  • 2JNU-QUT Joint Laboratory for Air Quality Science and Management, Jinan University, Guangzhou 511443, China
  • 3Air Quality Studies, Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Hong Kong
  • 4International Laboratory for Air Quality and Health, Queensland University of Technology, P.O. Box 2434, Brisbane, Queensland 4001, Australia
  • 5State Environmental Protection Key Laboratory of Regional Air Quality Monitoring, Guangdong Environmental Monitoring Center, Guangzhou 510308, China
  • 6Key Laboratory for Urban Habitat Environmental Science and Technology, School of Environment and Energy, Peking University Shenzhen Graduate School, Shenzhen 518055, China
  • 7State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China

Abstract. To investigate the atmospheric oxidative capacity (AOC) in forested high mountain areas adjacent to the photochemistry-active Pearl River Delta (PRD) region in southern China, one-month online observations of isoprene and its oxidation products methyl vinyl ketone (MVK) and methacrolein (MACR) were conducted at a national background station in Nanling Mountains in summer 2016. The results showed that the observed daytime isoprene levels (377±46pptv) were significantly lower in comparison with other forest sites within and outside China, although the sampling site was surrounded with subtropical evergreen broad-leaved trees which are strong isoprene emitters. Also, high daytime (MVK+MACR)isoprene ratios (1.9±0.5) were observed. Based on the observations, we hypothesized that the lower isoprene levels in the study forest might be attributable to a strong AOC in relation to the elevated regional complex air pollution. In further data analyses, high site-level concentrations of daytime OH (7.3±0.5×106moleculescm−3) and nighttime NO3 radicals (6.0±0.5×108moleculescm−3) were estimated by using a photochemical box model incorporating the master chemical mechanism (PBM-MCM), and high regional mixing ratios of OH (19.7±2.3×106moleculescm−3) during 09:00–15:00LT were also obtained by applying a parameterization method with measured aromatic hydrocarbons. And besides, high initial mixing ratios (1213±108pptv) and short atmospheric reaction time (0.27h) of isoprene during the day were derived by a sequential reaction approach. All these indicate that isoprene was rapidly and highly oxidized in this forest, which supports our hypothesis. The study suggests that the complex air pollution in the PRD may have significantly elevated the background AOC of the adjacent forests, and probably affects the regional air quality and ecological environment in the long term. The feedback of forest ecosystems to the increasing AOC in southern China warrants further studies.

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Short summary
The complex air pollution in the air-polluted Pearl River Delta (PRD) region in southern China has significantly elevated the background atmospheric oxidative capacity of the adjacent forests and subsequently lowered the levels of important biogenic volatile organic compounds, such as isoprene, which probably affect the regional air quality and ecological environment in the long term.
The complex air pollution in the air-polluted Pearl River Delta (PRD) region in southern China...