AMoN: An Initial Look at the First Two Years

Tom Butler1, Melissa Rury2, Gene Likens3, Gary Lear4 and Chris Lehmann5

The NADP passive ammonia monitoring network (AMoN) has been operating as a pilot study for over two years. The AMoN has consistently had approximately 20 sites measuring ambient NH3 concentrations in the United States. Each site deploys triplicate Radiello passive samplers for a two week sampling time period. Passive samplers were chosen as a low-cost, easily deployable sampler and the Radiello samplers have been shown to be reliable and accurate when compared to URG annular denuders. The two week samples provide seasonal and annual trends in NH3 concentrations which can be used to estimate NH3 deposition. NH3 has not been routinely measured in the United States and AMoN data will fill another gap of the total nitrogen budget. NADP wet deposition data has shown areas of increasing NH4+ deposition. While there are only 2 years of data from AMoN, increasing NH3 concentrations will pose a problem for PM2.5 attainment in areas that have reduced SO2 emissions but NO3- is still readily available for the formation of ammonium nitrate (NH4NO3). We have started to look at the seasonal and regional trends in NH3 concentrations measured at AMoN sites to highlight areas that might face challenges in meeting PM2.5 NAAQS regulations due to higher NH3 concentrations as a way to utilize the NH3 concentration measurements. Preliminary analysis of the AMoN data show that travel or field blanks generally range from 0.1 to 0.2 g NH3/m3 for the passive samplers, which may be an issue in areas of low NH3 concentrations. We estimated annual NH3 deposition at 21 AMoN sites using deposition velocities calculated within the CMAQ model. Seven sites show an annual NH3 deposition of over 4 kg-N/ha-yr , with annual concentrations generally above 3.0 g NH3/m3. For five collocated CASTNET sites (NY67, IL11, OK99, TX43, CO13) NH3 deposition accounted for 20% (NY67)to 60% (TX43 and CO13) of the total measured wet + dry N deposition.

1Cary Institute of Ecosystem Studies and Cornell University,211 Rice Hall, Cornell Univ. Ithaca, NY 14853 607 255-3580,
2Clean Air Markets Division, EPA, 202 343-9882,
3Cary institute of Ecosystem Studies, 845 677 5343,
4Clean Air Markets Division, EPA, 202 343-9159,
5NADP, 217 265-8512,