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Aerosol Ammonium in Urban Boundary Layer in Beijing

 Research


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 issue in China and many other countries. Since inorganic nitrogen (IN) contributes a large fraction to PM2.5andammonium (NH4+) is an important species of IN, researchers have paid specific attention to ambient NH3and particulate NH4+. 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.

Figure 1.The supplementary cover of ES&T Letters

Prof. Pingqing Fu’s group in Tianjin University collaborated with researchers fromChinese Academy of Sciences and Hong Kong Polytechnic University and together they investigated the concentrations and δ15N values of NH4+in PM2.5at three heights (8 meters, 120 meters and 260 meters) in a 325-meter-high tower in urban Beijing in 2015.

NH4+concentrations were lower during the Parade Blue Period (from August20th to September 3rd in 2015) due to strict air pollution control and favorable meteorological conditions, while δ15N-NH4+values were higher because regional transport of agricultural products (lower ratios of δ15N-NH4+) was less significant.

Vertical profiles of NH4+increasedwith heightwhileδ15N-NH4+decreased, indicating an enhanced contribution from regional transportat 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 NH3emissions are likely underestimated and that NH3slip from selective catalytic reduction processes should be included to explain the observed source contributions.

Figure 2.The graphical abstract of this study.

The research result was published inEnvironmental Science & Technology Letters(IF=6.934), as the supplementary cover article.

Paper link:https://pubs.acs.org/doi/10.1021/acs.estlett.9b00328

By the Institute of Surface-Earth System Science

Editors: Eva Yin & Doris Harrington