Precision of an Ambient Sequential Acid Aerosol Sampling System

Abstract

Abstract The repeatability (i.e., precision) of an automated sequential acid aerosol sampling system was investigated by collocating two identical systems on the roof of an air monitoring site in White Plains, New York (a suburb north of New York City) to collect 6 weeks of daily samples during August and September 1989. The variance of the resulting 41 paired samples was derived for each ion measured. The overall coefficients of variation for SO2- 4 and NH+ 4 were 7.7 percent and 13 percent, respectively, while estimates for H+ ranged from 13 percent to 19 percent. Linear regressions relating data from the paired systems resulted in high coefficients of determination (R2 > 0.93) for all ions. Also, time series plots of the daily ion differences indicated no significant difference between the systems for SO2- 4, NH+ 4, and H+. Paired t-tests of the daily differences affirmed the intersystem agreement for SO2- 4 and NH+ 4; however, this test also indicated a paired difference that was statistically significant but small, when compared to the percent coefficient of variation (%C.V.) for H+. Overall, these results demonstrate and quantify the reliability of this sampling system for characterizing the strong acid content of fine particulate matter. Jaques, P.A.; Thurston, G.D.; Kinney, P.L.; Gorczynski, J.E.: Precision of an Ambient Sequential Acid Aerosol Sampling System. Appl. Occup. Environ. Hyg. 8(4):313-316; 1993.