Environmental Factors that Affect Nylon and Teflon Filters used in Air Pollution Monitoring

Pamela Padgett
Atmospheric Deposition Unit, USDA Forest Service, Pacific Southwest Research
Riverside Fire Lab, 4955 Canyon Crest Dr, Riverside CA, 92507

Two proprietary filter media, Teflon (PTFE, PolyTetraFluoroEthylene) and Nylasorb (nylon) are used by both long term national monitoring networks and short term research-oriented monitoring projects. They are used in active monitoring systems such as the filter packs in the CASTNET program and in annular and honeycomb denuders, as well as passive monitoring systems used by many researchers and land managers. Both chemical and physical properties of the filters are engaged in trapping particulates and gasses. A series of experiments were conducted to evaluate the effects of ozone, relative humidity, and exposure time on the stability and reproducibility of these pollutant trapping materials. Variability in extract concentrations for NO3 - NH4 + and SO4 -2 within each experiment was <5% for all experiments, and little particulate decomposition was observed with extended operation and exposure. The presence of elevated ozone did, however, have a significant effect on capture or retention of HNO3 on Nylasorb filters; the greater the ozone concentration, the lower the extractable NO3 -. The effects of relative humidity were complicated by several other environmental factors, which will be highlighted in the presentation.