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　　我组成员在 Environmental Pollution 上发表文章：Shaonan Huang, Emily M.Elliott, David Felix, Yue peng Pan, Dong wei Liu, et al. Seasonal pattern of ammonium ¹⁵N natural abundance in precipitation at a rural forested site and implications for NH₃ source partitioning. Environmental Pollution. 2019. 

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　　Excess ammonia (NH₃) emissions and deposition can have negative effects on air quality and terrestrial ecosystems. Identifying NH₃ sources is a critical step for effectively reducing NH₃ emissions, which are generally unregulated around the world. Stable nitrogen isotopes (δ¹⁵N) of ammonium (NH₄⁺) in precipitation have been directly used to partition NH₃ sources. However, nitrogen isotope fractionation during atmospheric processes from NH₃ sources to sinks has been previously overlooked. Here we measured δ¹⁵N -NH₄⁺ in precipitation on a daily basis at a rural forested site in Northeast China over three years to examine its seasonal pattern and attempt to constrain the NH₃ sources. We found that the NH₄⁺ concentrations in precipitation ranged from 5 to 1265 μM, and NH₄⁺accounted for 65% of the inorganic nitrogen deposition (20.0 kg N ha^-1 yr^-1) over the study period. The δ¹⁵N values of NH₄⁺ fluctuated from -24.6 to +16.2‰ (average -6.5‰) and showed a repeatable seasonal pattern with higher values in summer (average -2.3‰) than in winter (average -16.4‰), which could not be explained by only the seasonal changes in the NH₃ sources. Our results suggest that in addition to the NH₃ sources, isotope equilibrium fractionation contributed to the seasonal pattern of δ¹⁵N -NH₄⁺ in precipitation, and thus, nitrogen isotope fractionation should be considered when partitioning NH₃ sources based on δ¹⁵N-NH₄⁺ in precipitation.