Gaseous ammonia is one of the main precursors for generating PM_2.5 in the atmosphere. In order to identifying the sources of ammonia more accurately with isotopic technique,and to alleviating PM_2.5 pollution in urban air, relevant data published in recent years have been collected and analyzed on sampling and quantifying of gaseous ammonia, determination or estimating of its nitrogen isotope ratio value, the nitrogen isotope compositions and fractionations for ammonia both in ambient air and emitted from different sources, the isotopic compositions of ammonium in atmospheric particulate matter and rainfall, as well as source apportionment of atmospheric ammonia. Several suggestions for future research have been accordingly proposed：The least amount of ammonia should be determined before collecting air samples with passive method in case of nitrogen isotope fractionation. Study may be strengthened on the nitrogen isotope compositions of ammonia from biomass combustion, natural soil, ocean, sewage plant, vegetation, and other potential sources. The mechanism on isotopic variation for ammonia from same emitting source could be further investigated. Both concentrations and isotopic compositions of gaseous ammonia and particulate ammonium perhaps may be simultaneously measured at higher temporal resolution,to understand the mechanism for nitrogen isotope fractionation in the process of ammonium forming. The isotopic fractionation of gaseous ammonia also should be deeply researched under different meteorological conditions and/or air contamination status.