Quality Assurance and Monitoring Results of the NADP's Passive Ammonia Network
Melissa Rury
U.S. Environmental Protection Agency
Ammonia is increasingly recognized as an important atmospheric pollutant as concentrations of oxides of sulfur and oxides of nitrogen change in the atmosphere. Ammonia is a principle component of PM2.5 as well as a being a significant source of nitrogen deposition to sensitive ecosystems. Sources of gaseous ammonia include fertilizer applied to crop lands, human and domesticated animal waste including hogs, cows and poultry and industrial chemical manufacturing. Ammonia reacts in the atmosphere to form fine particulate matter (PM2.5) via reactions with sulfuric and nitric acid. Until recently, long-term national ammonia concentration measurements have been overlooked. A national ammonia monitoring network is needed to characterize temporal and spatial trends, validate air quality models, calculate deposition fluxes, assess attempts to mitigate the eutrophication of sensitive ecosystems and meet the PM2.5 NAAQS criteria.
The proposed NADP Ammonia Monitoring Network (AMoN) is comprised of triplicate passive ammonia monitoring samplers located at over 20 sites across the United States. Passive samplers are useful for long-term monitoring as they can be sampled weekly or biweekly following NADP sampling schedules, and they do not require pumps, electricity, computers or data loggers. AMoN has been routinely collecting samples since the fall of 2007, and the current data set consists of approximately 850 weekly records. Samplers are replaced every two weeks and sent to the Illinois State Water Survey’s (ISWS) Central Analytical Laboratory (CAL) for analysis. More information on the AMoN is available at http://nadp.sws.uiuc.edu/nh3net/
Results from a multi-week statistical inter-comparison study using Radiello and Adapted Low-cost Passive High Absorption (ALPHA) samplers were used to confirm the selection of the Radiello passive sampler for network use. During the study, three sets of triplicate ALPHA and Radiello passive samplers were collocated with duplicate annular URG denuders as a reference method to quantify precision, accuracy and bias of the samplers at two sites: Bondville, IL and Cherokee Nation, OK. The precision between the triplicate passive samplers was evaluated against the denuder precision at the two sites. Results from the study showed both passive samplers had high precision values which were comparable to the denuders. To determine if spatial variability affected the precision of the samplers, three sets of triplicate Radiello and triplicate ALPHA samplers were deployed at three additional sites: Connecticut Hill, NY, Palo Duro, TX and Research Triangle Park, NC. Overall precision, accuracy, bias and cost were taken into consideration when recommending a passive sampler for AMoN.