Source apportionment of atmospheric ammonia before, during, and after the 2014 APEC summit in Beijing using stable nitrogen isotope signatures

Yunhua Chang,Xuejun Liu,Congrui Deng,Anthony J Dore,Guoshun Zhuang

doi:10.5194/acp-16-11635-2016

Abstract

Abstract. Stable nitrogen isotope composition (δ15N) offers new opportunities to address the long-standing and ongoing controversy regarding the origins of ambient ammonia (NH3), a vital precursor of PM2.5 (particulate matters with aerodynamic diameter equal or less than 2.5 µm) inorganic components, in the urban atmosphere. In this study, the δ15N values of NH3 samples collected from various sources were constrained using a novel and robust chemical method coupled with standard elemental analysis procedures. Independent of the wide variation in mass concentrations (ranging from 33 (vehicle) to over 6000 (human excreta) µg m−3), different NH3 sources have generally different δ15N values (ranging from −52.0 to −9.6 ‰). Significantly high δ15N values are seen as a characteristic feature of all vehicle-derived NH3 samples (−14.2 ± 2.8 ‰), which can be distinguished from other sources emitted at environmental temperature (−29.1 ± 1.7, −37.8 ± 3.6, and −50.0 ± 1.8 ‰ for livestock, waste, and fertilizer, respectively). The isotope δ15N signatures for a range of NH3 emission sources were used to evaluate the contributions of the different sources within measured ambient NH3 in Beijing, using an isotope mixing model (IsoSource). The method was used to quantify the sources of ambient NH3 before, during and after the 2014 Asia-Pacific Economic Cooperation (APEC) summit, when a set of stringent air quality control measures were implemented. Results show that the average NH3 concentrations (the overall contributions of traffic, waste, livestock, and fertilizer) during the three periods were 9.1 (20.3, 28.3, 23.6, and 27.7 %), 7.3 (8.8, 24.9, 14.3, and 52.0 %), and 12.7 (29.4, 23.6, 31.7, and 15.4 %) µg m−3, respectively, representing a 20.0 % decrease first and then a 74.5 % increase in overall NH3 mass concentrations. During (after) the summit, the contributions of traffic, waste, livestock, and fertilizer decreased (increased) by 56.7 (234.2), 12.0 (−5.0), 39.4 (120.8), and −87.7 % (−70.5 %) when compared with periods before (during) the summit, respectively, signifying that future NH3 control efforts in megacities like Beijing should prioritize traffic sector as well as livestock breeding. The results show that isotope ratio measurements of NH3 to be a valuable tool to quantify the atmospheric sources of NH3 in urban atmospheres.

Highlights

For more than a century, the Haber–Bosch process has been meeting the Earth’s increasing demand for grain and protein through nitrogen fertilizer (Erisman et al, 2008; Sutton et al, 2011)
Using N isotope as a tool to discriminate the contribution of various sources to ambient NH3 concentration requires (i) well-established N isotopic compositions of NH3 emission sources and (ii) well-constrained N isotope fractionation to allow separating different sources
These two independent studies determining the δ15N values of major NH3 sources arrive at the same conclusion: NH3 emitted from volatilized sources has relatively low δ15N values, allowing them to be distinctly differentiated from NH3 emitted from traffic sources that are characterized by relatively high δ15N values

Summary

Introduction

For more than a century, the Haber–Bosch process has been meeting the Earth’s increasing demand for grain and protein through nitrogen fertilizer (Erisman et al, 2008; Sutton et al, 2011). Unintentionally, increasing the application of ammonia (NH3) and its derivatives as fertilizer has altered the composition of the atmosphere (Fowler et al, 2009). Y. Chang et al.: Source apportionment of atmospheric ammonia largest contributor of NH3 emissions (Aneja et al, 2008), which cause cascading effects on human health, ecosystems, and climate (Galloway et al, 2003). Other non-agricultural sources must exist in urban areas (Chang, 2014; Sutton et al, 2000). Non-agricultural activities, are highly concentrated in urban areas and, could be supposed to be significant sources of NH3 in cities (Chang et al, 2012). Given the important role of urban NH3 emissions to form PM2.5 (particulate matters with aerodynamic diameter equal or less than 2.5 μm), NH3 emission reduction has been regarded as the key to curb severe haze pollution in Chinese megacities (Ye et al, 2011; Wang et al, 2011, 2013)

Methods

Results

Conclusion