Surface–atmosphere fluxes of volatile organic compounds in Beijing

Abstract

Abstract. Mixing ratios of volatile organic compounds (VOCs) were recorded in two field campaigns in central Beijing as part of the Air Pollution and Human Health in a Chinese Megacity (APHH) project. These data were used to calculate, for the first time in Beijing, the surface–atmosphere fluxes of VOCs using eddy covariance, giving a top-down estimation of VOC emissions from a central area of the city. The results were then used to evaluate the accuracy of 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 8.31 ± 8.5, 3.97 ± 3.9 and 1.83 ± 2.0 nmol m−2 s−1, respectively, in the summer. A large flux of isoprene was observed in the summer, with an average emission rate of 5.31 ± 7.7 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 the magnitude of VOC emissions at the local scale.

Characteristics of VOC Composition at Urban and Suburban Sites of New Delhi, India in Winter

“…In conjunction with the study at Mohali, our observations at New Delhi highlight the significance of open biomass burning in affecting the regional distribution of VOCs. The mean mixing ratio of methanol at the suburban site is comparable to the values reported for Beijing, China during the winter season (Acton et al, 2020). The higher mixing ratios of methanol in Beijing, China were attributed to emissions from industrial activities.…”

“…The results obtained in the present and previous studies (e.g., Acton et al, 2020;Sahu et al, 2017;, suggest significantly higher contributions of anthropogenic sources than those from biogenic sources in the urban regions of south-east Asia during the winter season.…”

“…In Sections 3.2 and 3.5, we examine the reasons for the higher levels of methanol at the suburban site. The concentrations of aromatic VOCs at both sites of New Delhi are found to be considerably lower than their values reported over Beijing, China (Acton et al, 2020;Gu et al, 2019), but are higher than those over Paris, France (Dolgorouky et al, 2012) and Zurich, Switzerland (Legreid et al, 2007). Higher levels of aromatics in New Delhi compared to a major urban region in western India (Ahmedabad) could be due to higher emissions and favorable meteorological conditions.…”

“…The contributions of secondary sources via photo-oxidation of primary VOCs are also significant in the urban atmosphere (Friedman et al, 2017;Yuan et al, 2012). Several studies have reported that alcohols (methanol and ethanol), ketones (especially acetone) and aldehydes (formaldehyde and acetaldehyde) are the most abundant OVOCs measured in the urban air (Acton et al, 2020;de Gouw et al, 2018;Wu et al, 2020). Nonetheless, the understanding of different emission and atmospheric processes of VOCs is important to assess their impact on air quality in complex urban environments (Warneke et al, 2013).…”

Emission Ratios and Source Identification of VOCs in Moscow in 2019–2020

“…Several studies in the literature have reported the evaluation of VOC emission inventories in urban areas using direct flux measurements in the surface layer [8,9], in situ aircraft measurements of air composition at various levels in the atmosphere [9][10][11][12] and satellite retrievals [5,13]. Over the last two decades, source-receptor modeling has also enabled the independent evaluation of the quality of emission inventories in various urban areas worldwide [14][15][16].…”