Surface–atmosphere fluxes of volatile organic compounds in Beijing

Acton, W. J. F. and Huang, Zhonghui and Davison, Brian and Drysdale, Will S. and Fu, Pingqing and Hollaway, Michael and Langford, Ben and Lee, James D. and Liu, Yanhui and Metzger, Stefan and Mullinger, Neil and Nemitz, Eiko and Reeves, Claire E. and Squires, Freya A. and Vaughan, Adam R. and Wang, Xinming and Wang, Zhaoyi and Wild, Oliver and Zhang, Qiang and Zhang, Yanli and Hewitt, C N (2020) Surface–atmosphere fluxes of volatile organic compounds in Beijing. Atmospheric Chemistry and Physics, 20 (23). pp. 15101-15125. ISSN 1680-7316

Abstract

Air pollution in Beijing has a major impact on public health and is therefore of concern to both policy makers and the general public. Volatile organic compounds (VOCs) are emitted from both anthropogenic and biogenic sources in urban environments and play an important role in atmospheric chemistry and hence atmospheric pollution through the formation of secondary organic aerosol and tropospheric ozone. Fluxes and mixing ratios of VOCs were recorded in two field campaigns as part of the Air Pollution and Human Health in a Chinese Megacity (APHH) project at the Institute of Atmospheric Physics (IAP) meteorological tower in central Beijing. These measurements represent the first eddy covariance flux measurements of VOCs in Beijing giving a top down estimation of VOC emissions from a central area of the city. These were then used to validate the Multi-resolution Emission Inventory for China (MEIC). The APHH winter and summer campaigns took place in November and December 2016 and May and June 2017 respectively. The largest VOC fluxes observed were of small oxygenated compounds such as methanol, ethanol + formic acid and acetaldehyde, with average emission rates of 8.02, 3.88 and 1.76 nmol m−2 s−1 respectively recorded in the summer campaign. In addition a large flux of isoprene was observed in the summer with an average flux of 4.63 nmol m−2 s−1. While oxygenated VOCs made up 60 % of the molar VOC flux measured, when fluxes were scaled by ozone formation potential and peroxyacyl nitrate (PAN) formation potential the high reactivity of isoprene and monoterpenes meant that these species represented 30 and 28 % of the flux contribution to ozone and PAN formation potential respectively. Comparison of measured fluxes with the emission inventory showed that the inventory failed to capture VOC emission at the local scale.