Ambient Ammonia Concentrations: A Data Review

Concentrations of fine particles (PM2.5) in the eastern half of the United States exceed the National Ambient Air Quality Standards in many urban areas and contribute to impaired visibility in scenic wilderness areas. Typically at least two-thirds of PM2.5 consists of ammonium sulfate and ammonium nitrate, which are formed from the reactions of ammonia with sulfuric and nitric acid, respectively. Thus an accurate characterization of ambient ammonia is critical to understanding its role in the formation of PM2.5.

Despite the clearcut need for ammonia measurements, it has not been widely or routinely monitored, due partly to the difficulty of measuring ammonia at typical ambient concentrations of 1-3 ppb. This poster reviews the ammonia data currently available from EPA’s Air Quality System (the national repository for aerometric data), as well as special study data from 1) the March-Midwest study sponsored by the Electric Power Research Institute, 2) urban measurements in Philadelphia, Tampa, and Houston made by researchers at Texas Tech University, 3) rural measurements by the Illinois State Water Survey, 4) source measurements made by the Minnesota Pollution Control Agency. Emission source, rural background, and urban measurements are compared. Diurnal, weekday/weekend, and seasonal patterns are characterized for each site type. Some apparent anomalies in the dataset are described and obvious gaps in spatial and temporal coverage are defined. This rudimentary review indicates that urban ammonia concentrations are typically two to three times greater than rural concentrations and exhibit weekday/weekend and diurnal variations that are consistent with mobile sources. Seasonally, ammonia is highest in the summer and lowest in the winter. Data are insufficient to determine trends over time.

⁽¹⁾ Lake Michigan Air Directors Consortium, 2250 E. Devon Ave., Suite 250, Des Plaines, IL 60018
⁽²⁾ Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409-
*Corresponding author