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ACID AEROSOL MEASUREMENT METHODS: A SUMMARY OF U.S. EPA INTERCOMPARISONS
Citation:
Ellestad, T. ACID AEROSOL MEASUREMENT METHODS: A SUMMARY OF U.S. EPA INTERCOMPARISONS. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/A-93/170 (NTIS PB93221885).
Description:
Studies of human exposure to acid aerosols have been underway for several years, leading to the need to intercompare measurement methods for acidic aerosol concentrations. ver the past few years the U.S. EPA has sponsored several intercomparisons of the methods in use. ost of these methods are similar; nevertheless, some differences exist among the samplers, as well as in details of their operation. he studies have included single component aerosols of sulfuric acid and ammonium bisulfate, photochemical aerosols, a sequence of compounds chosen to test for on-filter neutralization by ammonium nitrate, the addition of alkaline dust, laboratory-spiked samples, and atmospheric aerosol samples. hese studies were designed to establish both intra- and interlaboratory precision and to attempt to separate the effects of differences in flow rate, extraction, and analysis. ll major groups that are active in acid aerosol measurement have participated. hese studies have not been done for the purpose of choosing a best method, but rather to document the current level of performance and to suggest items for improvement. he results of these studies are that intralab precision (stated as the coefficient of variation) is typically 5-10 percent for any lab, while total precision among labs is 10-25 percent. owever, in most cases of poorer total precision, the cause is either a systematic bias between two or more labs or inadequate low-level performance by one or more labs. hese findings suggest that additional standardization in methodology is warranted.