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Ammonia emissions are associated with many agricultural operations including animal and poultry operations, waste and wastewater treatment operations, and fertilizer and manure land applications. The fate of ammonia released to atmosphere is affected by interaction with other gases, aerosols, and fine particles. These interactions affect the gas-to-particle conversion. This process alters ammonia concentrations downwind from agricultural operations. However, experimental research and modeling of the gas-to-particle conversion processes in ammonia-rich environments is generally limited. This paper summarizes the state-of-the-art knowledge related to gas-to-particle conversion of ammonia.

Ammonia and inorganic acid gases emitted from livestock and poultry operations and manure treatment, handling and application can affect air quality by formation of secondary particulate in the fine, PM2.5 range (a regulated air pollutant). The process of gas-to-particle conversion of relatively short-lived gaseous ammonia to more persistent fine particulate can affect local and regional air quality far away from the agricultural sources. Emissions of ammonia from livestock and poultry operations can potentially be detrimental to the air quality in non-compliance areas. Several models for the formation of fine PM from substrates such as ammonia are available and have been used for air quality modeling on a local and regional scale. These models can be adapted or modified to include emissions of ammonia and acid gases from livestock and poultry operations.

More research is needed to improve the knowledge related to the role of ammonia gas-to-particle conversion. These needs include: (1) simultaneous field measurements of ammonia and acid gases at typical livestock and poultry sources, (2) development of emission factors for ammonia and acid gases, (3) incorporation of ammonia from agricultural sources to local and regional air quality models, and (4) modeling the fate of ammonia and acid gases emissions from livestock and poultry operations.