Factors that influence the collection and measurement of atmospheric sulfate were investigated. Special emphasis was given to those factors that cause the formation of extraneous sulfate during the sampling process. The factors considered were filter type and composition, ambient SO2 concentration, temperature, relative humidity, ambient gas composition, sampling time and rate, storage time and conditions, and the presence of potential oxidation catalysts in the particular catch. The approach of the investigation was twofold. After conducting an extensive laboratory program to identify and quantify significant sulfate generating interactions, a brief field study was performed to test the significance of the laboratory observations under typical field operating conditions. The results of this investigation indicated that the most significant cause of sulfate sampling error is the interaction of basic filter components with ambient SO2. This interaction is affected by ambient atmospheric conditions. A relationship based on established chemistry was developed for the prediction of sulfate error caused by this interaction. Recommendations of filter media appropriate for ambient sulfate monitoring and further development of a methodology are included.

"EPA 600/2-77/076." EPA contract no. 68-02-1784, EPA project officer: Eva Wittgenstein. Includes bibliographical references (pages 46-47).