Sources, Variations, and Effects on Air Quality of Atmospheric Ammonia

Abstract

Purpose of Review

As the most abundant alkaline trace gas in the atmosphere, NH₃ plays a critical role in the formation of atmospheric particulate matter and nitrogen cycling in ecosystems. NH₃ emissions have been increasing globally over the past few decades. To provide a clearer understanding of atmospheric NH₃, this paper presents a systematic review of the literature on the sources and variability of atmospheric NH₃ and describes the contribution of atmospheric NH₃ to PM_2.5.

Recent Findings

(1) The primary source of atmospheric NH₃ emissions is agriculture; other sources include combustion-related emissions and volatilization from soil and oceans. However, recent studies have revealed the major role of nonagricultural sources in urban areas. (2) The spatiotemporal variability of atmospheric NH₃ is complex, and its mechanisms are not entirely clear. (3) Atmospheric NH₃ can participate in multiple atmospheric chemical processes and to the formation of fine particulate matter.

Summary

This review summarizes the latest knowledge on the sources and variability of atmospheric NH₃ and highlights the necessity of controlling atmospheric NH₃ emissions. However, significant knowledge gaps still exist in understanding the sources, trends, and effects of atmospheric NH₃. Therefore, further research is essential to investigate the influencing factors and environmental effects of atmospheric NH₃ concentrations, providing a scientific basis for the development of effective NH₃ control strategies.