Agricultural sources and non-agricultural emissions contribute to gaseous ammonia (NH₃) that plays a vital role in severe haze formation. Qualitative and quantitative contributions of these sources to ambient PM_2.5 (particulate matter with an aerodynamic equivalent diameter below 2.5 µm) concentrations remains uncertain. Stable nitrogen isotopic composition (δ¹⁵N) of NH₃ and NH₄⁺ (δ¹⁵N(NH₃) and δ¹⁵N(NH₄⁺), respectively) can yield valuable information about its sources and associated processes. This review provides an overview of the recent progress in analytical techniques for δ¹⁵N(NH₃) and δ¹⁵N(NH₄⁺) measurement, sampling of atmospheric NH₃ and NH₄⁺ in the ambient air and their sources signature (e.g., agricultural vs. fossil fuel), and isotope-based source apportionment of NH₃ in urban atmosphere. This study highlights that collecting sample that are fully representative of emission sources remains a challenge in fingerprinting δ¹⁵N(NH₃) values of NH₃ emission sources. Furthermore, isotopic fractionation during NH₃ gas-to-particle conversion under varying ambient field conditions (e.g., relative humidity, particle pH, temperature) remains unclear, which indicates more field and laboratory studies to validate theoretically predicted isotopic fractionation are required. Thus, this study concludes that lack of refined δ¹⁵N(NH₃) fingerprints and full understanding of isotopic fractionation during aerosol formation in a laboratory and field conditions is a limitation for isotope-based source apportionment of NH₃. More experimental work (in chamber studies) and theoretical estimations in combinations of field verification are necessary in characterizing isotopic fractionation under various environmental and atmospheric neutralization conditions, which would help to better interpret isotopic data and our understanding on NH_x (NH₃ + NH₄⁺) dynamics in the atmosphere.

农业来源和非农业排放会产生气态氨 (NH ₃ )，而气态氨在严重雾霾的形成中起着至关重要的作用。这些来源对环境 PM _2.5（空气动力学当量直径低于 2.5 µm 的颗粒物）浓度的定性和定量贡献仍然不确定。_{NH 3}和NH ₄ ⁺的稳定氮同位素组成(δ ¹⁵ N) （分别为δ ¹⁵ N(NH ₃ ) 和δ ¹⁵ N(NH ₄ ⁺ )）可以提供关于其来源和相关过程的有价值信息。本综述概述了 δ 分析技术的最新进展¹⁵ N(NH ₃ ) 和 δ ¹⁵ N(NH ₄ ⁺ ) 测量、环境空气中大气 NH ₃和 NH ₄ ⁺的采样及其来源特征（例如，农业与化石燃料），以及基于同位素的来源解析城市大气中的 NH ₃。这项研究强调，收集完全代表排放源的样本仍然是对 NH _{3排放源的 δ} ¹⁵ N(NH ₃ ) 值进行指纹识别的挑战。_{此外，NH 3}期间的同位素分馏在不同的环境现场条件（例如，相对湿度、颗粒 pH 值、温度）下气体到颗粒的转化仍不清楚，这表明需要更多的现场和实验室研究来验证理论上预测的同位素分馏。因此，本研究得出结论，缺乏精细的 δ ¹⁵ N(NH ₃ ) 指纹和对实验室和现场条件下气溶胶形成过程中同位素分馏的充分理解是基于同位素的 NH _{3源解析的限制}. 在表征各种环境和大气中和条件下的同位素分馏时，需要更多的实验工作（在室内研究中）和结合现场验证的理论估计，这将有助于更好地解释同位素数据和我们对 NH _x (NH ₃ + NH ₄ ⁺ ) 大气中的动态。