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Piercing the haze

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Science  14 Sep 2018:
Vol. 361, Issue 6407, pp. 1060-1063
DOI: 10.1126/science.361.6407.1060

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  • Isotopic evidence for non-agricultural sources of aerosol ammonium in the urban atmosphere
    • Yuepeng Pan, Prof., Institute of Atmospheric Physics, Chinese Academy of Sciences
    • Other Contributors:
      • Shili Tian, Dr., Institute of Atmospheric Physics, Chinese Academy of Sciences
      • Yunting Fang, Prof., Institute of Applied Ecology, Chinese Academy of Sciences
      • Xiaying Zhu, Dr., National Climate Center, China Meteorological Administration
      • Greg Michalski, Prof., Department of Chemistry, Department of Earth, Atmospheric, and Planetary Sciences, Purdue University
      • Yuesi Wang, Prof., Institute of Applied Ecology, Chinese Academy of Sciences

    It is interesting that ammonium nitrate contributed three quarters of fine particles in the Salt Lake City region and that during winter months the ammonia concentrations were higher than expected (1), which are similar to the North China Plain (2). Knowing the source of ammonium is therefore crucial to policy makers on reducing the concentrations of particulate matter. Here we summarized a carefully executed application of existing stable nitrogen isotope measurement and mass-balance techniques to a very important problem: understanding source contributions to atmospheric ammonium in urban environment (2).

    Compared to the conventional inventory method, coupling stable isotopes and aerosol chemistry is a novel approach that can help quantify the sources of ambient ammonia on the basis of the stable isotopic composition of ammonia (δ15N-ammonia) for various endmembers (3). However, isotope-based source apportionment of aerosol ammonium is challenging because the δ15N values of ammonium may differ from the precursor ammonia (4, 5). The difference in isotopic signals between ammonium and ammonia depends on equilibrium isotopic enrichment factors and the distribution of aerosol ammonium and ammonia gas (6-8). When ammonia is in deficit (e.g., in the marine atmosphere), the aerosols collected are close to acidic, recycling and fractionation between ammonia and ammonium are unlikely, and hence, the δ15N values of ammonium reflect their original sources of ammonia (9). Wh...

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    Competing Interests: None declared.