The Ammonia CASTNET CSN Study (ACCS) Overview and Test Phase Results

Christopher Rogers1, Kevin Mishoe2, Michael Smith2, Marcus Stewart2 and H. Kemp Howell2

The primary purpose of the Ammonia CASTNET CSN Study (ACCS) is to conduct a reactive nitrogen (Nr) inter-comparison study at five CASTNET sites for one year. Currently, the traditional CASTNET 3-stage filter pack captures particulate ammonium (NH4+) and nitrate (NO3-) on the first (Teflon) filter. The goals of the ACCS are to:

  1. Assess the precision, accuracy, and bias of passive ammonia samplers,
  2. Test a traditional CASTNET filter pack with an additional fourth stage filter impregnated with phosphorus acid (HPO3) to collect atmospheric NH3 and any volatilized NH4+,
  3. Characterize Met One SuperSASS mini-parallel plate denuders for NH3 collection, and
  4. Compare Met One SuperSASS ion module species collection with traditional CASTNET 3-stage filter pack species collection.

Duplicate annular denuder systems (ADS) will be used as the reference method. Site selection was based on proximity to predicted or known ammonia emissions sources, site operator capability, and collocation with the National Atmospheric Deposition Program (NADP) Ammonia Monitoring Network (AMoN). Current AMoN sites are measuring NH33 concentrations at a 2-week interval as an average of results obtained from triplicate Radiello passive samplers. Other sampling types will be run for two 1-week periods every six weeks.

Prior to the start of field sampling on August 31, several test studies were conducted at the Gainesville, FL MACTEC facility. Two problems were encountered during testing. First, the initial ADS design featured a nylon filter for the collection of particles, which proved to be inadequate as there was evidence of particle breakthrough. A Teflon filter was added to the ADS for the collection of particles, and results improved. The second problem involved the 4-stage filter pack. Expected results were not obtained. No NH3 was collected by the H3PO3 impregnated filter. It appears that in high humidity environments use of a 4-stage filter pack is not viable. The NH3 may react with SO2 collected by a hydrated potassium-carbonate (K2CO3) impregnated filter prior to encountering the H3PO3 impregnated filter. Because of this issue, 4-stage CASTNET-style filter packs will not be included during the first several ACCS sampling periods. Additional testing of other configurations will be performed, and it is hoped that a modified CASTNET filter pack will join the study by its midpoint.

1MACTEC Engineering & Consulting, Inc., 3901 Carmichael Ave., Jacksonville, FL 32207, 904.391.3744,
2 MACTEC Engineering & Consulting, Inc., 404 SW 140th Terr., Newberry, FL 32669