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

D. Gong; H. Wang; H. Wang; S. Zhang; Y. Wang; S. C. Liu; H. Guo; M. Shao; C. He; C. He; D. Chen; L. He; L. Zhou; L. Morawska; L. Morawska; Y. Zhang; B. Wang; B. Wang

doi:10.5194/acp-18-14417-2018

Atmospheric Chemistry and Physics (Oct 2018)

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

D. Gong,
H. Wang,
H. Wang,
S. Zhang,
Y. Wang,
S. C. Liu,
H. Guo,
M. Shao,
C. He,
C. He,
D. Chen,
L. He,
L. Zhou,
L. Morawska,
L. Morawska,
Y. Zhang,
B. Wang,
B. Wang

Affiliations

D. Gong: Institute for Environmental and Climate Research, Jinan University, Guangzhou 511443, China
H. Wang: Institute for Environmental and Climate Research, Jinan University, Guangzhou 511443, China
H. Wang: JNU-QUT Joint Laboratory for Air Quality Science and Management, Jinan University, Guangzhou 511443, China
S. Zhang: Institute for Environmental and Climate Research, Jinan University, Guangzhou 511443, China
Y. Wang: Air Quality Studies, Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Hong Kong
S. C. Liu: Institute for Environmental and Climate Research, Jinan University, Guangzhou 511443, China
H. Guo: Air Quality Studies, Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Hong Kong
M. Shao: Institute for Environmental and Climate Research, Jinan University, Guangzhou 511443, China
C. He: JNU-QUT Joint Laboratory for Air Quality Science and Management, Jinan University, Guangzhou 511443, China
C. He: International Laboratory for Air Quality and Health, Queensland University of Technology, P.O. Box 2434, Brisbane, Queensland 4001, Australia
D. Chen: State Environmental Protection Key Laboratory of Regional Air Quality Monitoring, Guangdong Environmental Monitoring Center, Guangzhou 510308, China
L. He: Key Laboratory for Urban Habitat Environmental Science and Technology, School of Environment and Energy, Peking University Shenzhen Graduate School, Shenzhen 518055, China
L. Zhou: Institute for Environmental and Climate Research, Jinan University, Guangzhou 511443, China
L. Morawska: JNU-QUT Joint Laboratory for Air Quality Science and Management, Jinan University, Guangzhou 511443, China
L. Morawska: International Laboratory for Air Quality and Health, Queensland University of Technology, P.O. Box 2434, Brisbane, Queensland 4001, Australia
Y. Zhang: State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China
B. Wang: Institute for Environmental and Climate Research, Jinan University, Guangzhou 511443, China
B. Wang: JNU-QUT Joint Laboratory for Air Quality Science and Management, Jinan University, Guangzhou 511443, China

DOI: https://doi.org/10.5194/acp-18-14417-2018
Journal volume & issue: Vol. 18
pp. 14417 – 14432

Abstract

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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±46 pptv) 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±0.5×106 molecules cm−3) and nighttime NO3 radicals (6.0±0.5×108 molecules cm−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±2.3×106 molecules cm−3) during 09:00–15:00 LT were also obtained by applying a parameterization method with measured aromatic hydrocarbons. And besides, high initial mixing ratios (1213±108 pptv) and short atmospheric reaction time (0.27 h) 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.

Published in Atmospheric Chemistry and Physics

ISSN: 1680-7316 (Print); 1680-7324 (Online)
Publisher: Copernicus Publications
Country of publisher: Germany
LCC subjects: Science: Physics; Science: Chemistry
Website: http://www.atmospheric-chemistry-and-physics.net/

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