Artifact particulate sulfate and nitrate formation on filter media

Abstract

Laboratory and atmospheric sampling studies were performed to evaluate glass fiber, quartz and Teflon filters for their abilities to form artifact particulate sulfate and nitrate with SO 2and HNO 3, respectively. The glass fiber filters were the types employed by the U.S. EPA as well as many State and local agencies for hi-vol particle sampling in the period 1977–1982. In 24-h laboratory trials, the sulfate artifact with the glass fiber filters ranged from 32 to 59μgcm −2 (8–15μg m −3 at simulated hi-vol sampling rates). With the exception of Whatman QMA, the ‘quartz’ and Teflon filters collected very low levels of SO 2. At nitric acid dosages representative of those in atmospheric sampling, the glass fiber filters retained > 94% of the HNO 3; the ‘quartz’ filters, 33 to > 99%; and Teflon filters, <2 % of the HNO 3,. Because of competing acidic species in ambient air, these represent upper limits to the values to be expected in atmospheric sampling. Over the dosage range evaluated, artifact particulate sulfate and nitrate formation on ‘quartz’ and Teflon filters were highly correlated to each other from one filter to another, with a 4:1 molar ratio of nitrate: sulfate. The sulfate artifact in atmospheric sampling with Pallflex ‘quartz’ filters was consistent with laboratory findings while the nitrate artifact was much lower than predicted.