1B.5 Source Apportionment, Spatiotemporal Variations of Atmospheric Ammonia in China: Focus on Severe Haze Episodes in Urban Beijing

Monday, 8 January 2018: 9:45 AM
Room 18CD (ACC) (Austin, Texas)
Yuepeng Pan, AES, Beijing, China

The reduction of ammonia emissions is urgently needed due to its role in haze pollution and nitrogen deposition. However, the spatial distribution and seasonal variations of ammonia across China are unclear. The observation gaps motivate us to design a study to investigate the atmospheric ammonia on a national scale. Based on the year round observation at 50 sites in China, we confirm that the abundant concentrations of ammonia spotted in typical agricultural regions of China, especially North China Plain. On urban scale, however, the relative contributions of individual ammonia sources are unclear, and debate remains over whether agricultural emissions dominate atmospheric ammonia in urban areas. Based on the chemical and isotopic measurements of size-resolved aerosols in urban Beijing, China, we find that the natural abundance of 15N (expressed using δ15N values) of NH4+ in fine particles varies with the development of haze episodes, ranging from −37.1‰ to −21.7‰ during clean/dusty days (relative humidity: ~40%), to −13.1‰ to +5.8‰ during hazy days (relative humidity: 70−90%). After accounting for the isotope exchange between NH3 gas and aerosol NH4+, the δ15N value of the initial NH3 during hazy days is found to be −14.5‰ to −1.6‰, which indicates fossil fuel-based emissions. These emissions contribute 90% of the total NH3 during hazy days in urban Beijing. On an annual basis, 40−52% of the “initial NH3 concentrations” in urban Beijing arise from fossil fuel emissions, which are episodically enhanced by stagnant weather preceding the passage of cold fronts. This work demonstrates the analysis of δ15N values of aerosol NH4+ to be a promising new tool for partitioning atmospheric NH3 sources. These results provide strong evidence for the contribution of non-agricultural sources to NH3 in urban regions and suggest the prioritization of controlling these emissions for haze regulation.
- Indicates paper has been withdrawn from meeting
- Indicates an Award Winner