Passive Ammonia Monitoring in the Central U.S.

Gary Lear
US Environmental Protection Agency,
Clean Air Markets Division,
Washington, D.C. USA

Atmospheric scientists need ambient ammonia concentration measurements for use in air quality models and other studies. Unfortunately instrumental ammonia monitors are both expensive and difficult to operate for extended periods. To minimize costs and operate without electricity, for the past 2 years we have deployed Radiello® passive diffusion ammonia samplers at over 20 site network in the central U.S. At the Bondville, IL site (IL11) ammonia concentrations were measured concurrently using a standard pumped denuder method along with three alternative types of passive diffusion samplers Ogawa, Alpha and custom-built.

Typical network winter and spring two-week ammonia concentrations range between 0.5 and 10 ppbv. The highest averages are seen in SW Minnesota (8-10 ppb), with the highest network concentration reported in SE Kansas (15 ppb). The Texas panhandle site is consistently 4 to 6 ppb, and the lowest network concentrations were measured in New York (< ½ ppb). The Radiello system provides consistent results and good agreement with the denuder value for ammonia concentration. Disadvantages are its high cost and relatively high field blank values. Of the alternatives, the Alpha samplers appear to offer similar performance at lower overall cost of the Radiellos.