A018-07
Unmanned Aerial Vehicle (UAV) Measurements of Volatile Organic Compounds over a Subtropical Forest in China and Implications for Emission Heterogeneity

Monday, 7 December 2020: 11:16
Virtual
Yaowei Li1, Ben Liu2, Jianhuai Ye3, Tianjiao Jia4, Jiayin Sun5, Cheng Wu6, Scot T. Martin3, Yongjie Li2 and Qi Chen4, (1)Harvard University, School of Engineering and Applied Sciences, Cambridge, MA, United States, (2)University of Macau, Department of Civil and Environmental Engineering, Macau, China, (3)Harvard University, Cambridge, MA, United States, (4)Peking University, State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Beijing, China, (5)Jinan university, Institute of Mass Spectrometer and Atmospheric Environment, Guangzhou, China, (6)Jinan University, Institute of Mass Spectrometer and Atmospheric Environment, Guangzhou, China
Recorded Presentation
Abstract:
Vertical measurements of atmospheric volatile organic compounds (VOCs) are important for understanding their emissions from the ecosystem and subsequent atmospheric oxidation. Atmospheric sampling onboard a multicopter unmanned aerial vehicle (UAV), serving as an economical and flexible measurement technique, collects valuable VOC data sets at intermediate spatial scales of 100s of meters. Herein, we deployed a UAV-based VOC sampler over a subtropical forest in South China and conducted VOC samplings at 25 m and 100 m over the canopy of a valley forest conjunct to a slope forest. The collected VOC samples were analyzed offline by gas chromatography-mass spectrometry. Isoprene and α-pinene, two dominant biogenic VOCs, showed day-to-night variations that were consistent with their emission patterns. High ratios of the concentrations of methacrolein and methyl vinyl ketone to isoprene suggest a possible fast atmospheric oxidation of isoprene. In addition, high concentrations of ozone and aromatic VOCs were observed, indicating a strong influence of anthropogenic pollution in this subtropical forest, consistent with previous ground-based studies. The concentration differences at the two sampling heights were significant for biogenic VOCs, especially for isoprene, but not for aromatic VOCs. Results by a gradient transport model suggest that the heterogeneity of isoprene emissions along the mountain slope was necessary to explain the concentration gradients. Strong eddy diffusion caused by valley breeze also contributed to the observed differences. This emission heterogeneity at intermediate scales (i.e., several hundred meters on a mountain slope) is not well represented in most present-day biosphere emission models for subtropical forests. Our study provides unique vertical measurements for biogenic, aromatic, and oxygenated VOCs that are useful in assessing the dynamics of near-surface VOC emission and chemistry.
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