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

Purpose of Review As the most abundant alkaline trace gas in the atmosphere, NH 3 plays a critical role in the formation of atmospheric particulate matter and nitrogen cycling in ecosystems. NH 3 emissions have been increasing globally over the past few decades. To provide a clearer understanding of atmospheric NH 3 , this paper presents a systematic review of the literature on the sources and variability of atmospheric NH 3 and describes the contribution of atmospheric NH 3 to PM 2.5 . Recent Findings (1) The primary source of atmospheric NH 3 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 NH 3 is complex, and its mechanisms are not entirely clear. (3) Atmospheric NH 3 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 NH 3 and highlights the necessity of controlling atmospheric NH 3 emissions. However, significant knowledge gaps still exist in understanding the sources, trends, and effects of atmospheric NH 3 . Therefore, further research is essential to investigate the influencing factors and environmental effects of atmospheric NH 3 concentrations, providing a scientific basis for the development of effective NH 3 control strategies.