Effect of Different Types of Glass Filters on Total Suspended Participates and Their Chemical Composition

Abstract

Atmospheric particulates, collected on four different types of filters (Gelman A, AE, Spectro Grade, and a special batch of Type A supplied by the EPA) in a side-by-side comparison showed differences in total suspended particulates (TSP) and lead loading as high as 20 and 17 percent, respectively (using Gelman A as a reference). The differences in sulfate and nitrate were even greater, running as high as 49 and 219 percent, respectively. Catalytic conversion of SO/sub 2/ and NO/sub 2/ to particulate sulfate and nitrate on contact with the filter surface is believed responsible for the anomalously high values observed. For all of these parameters (i.e., TSP, lead, sulfate, and nitrate) Gelman's Spectro Grade and AE filters yielded the highest values and Gelman Type A the lowest. Based on these results and assuming that catalytic conversion produces erroneously high data, one might be inclined to conclude that Type A was superior to the others; however, additional studies on collection efficiencies and interaction effects with filter constituents would be required before such a conclusion would be warranted. The results do indicate that the type of filter medium used in hi-vol sampling has a pronounced effect on the results. It therefore becomes imperativemore » that all agencies involved in air monitoring surveillance standardize on a single filter medium as soon as possible. This priority becomes even more urgent in view of the 25 ..mu..g/m/sup 3/ sulfate standard recently imposed by the California Air Resources Board. The long-range goal should be the development of a filter for which the catalytic conversions are either eliminated or at least held to a minimum (i.e., 5 percent or less).« less