Abstract
The direct, nondestructive, infrared transmission measurement of fine particles (<2.5 μm) on Teflon® filters was successfully used to unambiguously identify and to quantify ammonium bisulfate in particle samples collected from the ambient air. The samples were collected at 10 L/min over 23 hours for 24 consecutive summer days (21 July-14 August) in 1991 in a rural setting near State College, PA. These measurements were combined with wet chemical measurements of the same samples to infer the partition of particulate sulfate as ammonium sulfate, ammonium bisulfate, and sulfate associated with excess free hydrogen ion. A second set of independent wet chemical measurements of samples taken during the same time period were included in the analysis. The evidence for particle reactions on the filter and of some neutralization of acid sulfate by ammonia during sample processing is examined. Highly variable sulfate speciation is observed, including sulfuric acid and ammonium sulfate without ammonium bisulfate. Subject to the current limitations of the technique, sulfate as ammonium sulfate, ammonium bisulfate, and sulfuric acid is estimated in the approximate proportions of 3.0:5.5:1 for the overall study.
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