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Aerosol Ammonium in the Urban Boundary Layer in Beijing: Insights from Nitrogen Isotope Ratios and Simulations in Summer 2015

2019-07-19 234


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The supplementary cover of ES&T Letters

In recent years, many studies have focused on the chemical composition, sources and formation mechanisms of atmospheric fine aerosols (PM2.5), as haze pollution has become a severe scientific and political issue in China and many other countries. Since inorganic nitrogen (IN) contributes a large fraction to PM2.5 and ammonium (NH4+) is an important species of IN, ambient NH3 and particulate NH4+ have been paid specific attention to. Most previous studies focused on the sources of aerosol NH4+ at a ground level. However, to date, little is known about the vertical distribution of aerosol NH4+ and its stable nitrogen isotope ratios in the urban boundary layer.

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The graphical abstract of this study

This study investigates the concentrations and δ15N values of NH4+ in PM2.5 at three heights (8, 120 and 260 m) on a 325-meter tower in urban Beijing. NH4+ concentrations were lower during the Parade Blue Period (20 August3 September 2015) due to strict air pollution control and favorable meteorological conditions, while δ15N-NH4+ values were higher because regional transport of agricultural sources (lower ratios of δ15N-NH4+) was less significant. Vertical profiles of NH4+ increased with height while δ15N-NH4+ decreased, indicating an enhanced contribution from regional transport at high altitudes.The “MixSIAR” isotopic mixing model results indicate that agricultural emission contributed 47% to the ground-surface NH4+ and reached 51?56% at high altitudes. Results from a source-oriented air quality model and the 2016 MEIC emission inventory suggest that non-agricultural NH3 emissions are likely underestimated and NH3 slip from selective catalytic reduction processes should be included to explain the observed source contributions.

This work from Prof. Pingqing Fu’s group in Tianjin University and collaborators from Chinese Academy of Sciences, The Hong Kong Polytechnic University, etc., has been recently published on Environmental Science & Technology Letters (IF=6.934), and is selected as the supplementary cover article for the current issue.

Libin Wu#, Hong Ren#, Peng Wang, Jing Chen, Yunting Fang, Wei Hu, Lujie Ren, Junjun Deng, Yu Song, Jie Li, Yele Sun, Zifa Wang, Cong-Qiang Liu, Qi Ying, Pingqing Fu*. 2019. Aerosol Ammonium in the Urban Boundary Layer in Beijing: Insights from Nitrogen Isotope Ratios and Simulations in Summer 2015. Environmental Science & Technology Letters 6: 389–395. 

Link to the articlehttps://pubs.acs.org/doi/10.1021/acs.estlett.9b00328