Diffusion denuders have been developed to concurrently remove nitric acid and permit particles to pass unattenuated. The particulate matter may then be collected on specialized filters that minimize further volatilization. This technique allows the measurement of nitric acid and particulate nitrate with a minimum of removal artifacts caused by the volatilization and condensation of ammonium nitrate. There is a significant body of literature describing the suitability of using such denuders and filters for this purpose in studies using ambient air (Allegrini et al., 1994). There is, however, little information on the quantitative testing of these substrates to remove nitric acid while allowing other nitrogenous gases, such as nitrogen dioxide, nitrous acid, and peroxyacetyl nitrate, to pass through freely. Removal inefficiency of the denuder for nitric acid will bias the nitric acid low and the particulate nitrate high, while collecting the other nitrogenous species will bias both high. In addition, there is little published information on the removal efficiency of an aluminum honeycomb denuder that is currently offered as a commercial product.

Project officer: Brenda Millar. College of Engineering-Center for Environmental Research and Technology, University of California, Riverside, CA "April 2002." "EPA-454/R-02-011."

Diffusion denuders have been developed to concurrently remove nitric acid and permit particles to pass unattenuated. The particulate matter may then be collected on specialized filters that minimize further volatilization. This technique allows the measurement of nitric acid and particulate nitrate with a minimum of removal artifacts caused by the volatilization and condensation of ammonium nitrate. There is a significant body of literature describing the suitability of using such denuders and filters for this purpose in studies using ambient air (Allegrini et al., 1994). There is, however, little information on the quantitative testing of these substrates to remove nitric acid while allowing other nitrogenous gases, such as nitrogen dioxide, nitrous acid, and peroxyacetyl nitrate, to pas through freely. Removal inefficiency of the denuder for nitric acid will bias the nitric acid low and the particulate nitrate high, while collecting the other nitrogenous species will bias both high. In addition, there is little published information on the removal efficiency of an aluminum honeycomb denuder that is currently offered as a commercial product. The primary objectives were to: ¨Determine the short-term efficiency and capacity of chemically coated filters and diffusion denuders that are currently using in EPA's National PMb2s.b5s Chemical Speciation Network to collect nitric acid and related nitrogenous species under ambient air conditions. ¨ Assess the potential interferences associated with the collection of gases on reactive filters that follow these denuders that were not efficiently removed by the denuders.