Static charge present on a filter contributes substantial error to low-level mass measurements. The measurement and sources of static charge are not well understood and this article presents a fundamental method of static charge measurement. As predicted by other researchers, triboelectric charging was found to generate significant static charge on a filter when using 2007 Diesel particulate matter (PM) measurement protocols. Measurements made using our method indicate that PM filters are rapidly and effectively neutralized by 210Polonuim (210Po) sources. The neutralization of charge occurred exponentially with characteristic time constants (the time it takes for the charge on the filter to decay by 63%) of 0.4 and 0.7 s, depending on the strength of the source. The experimental neutralization time constants were consistent with theory. The charge remaining on highly charged 47 mm Teflon and TX40 filters after 5 s of neutralization with year old 210Po sources biased the true filter mass by <1 μg when the filters were weighed with a 1 μg resolution Cahn microbalance.
Bibliographical noteFunding Information:
This work was funded by Donaldson Company, Inc. We acknowledge the technical and editorial advice provided by Winthrop Watts (UMN), David Dikken (Measurement Technology Laboratories), and Richard Chase (formally of Ford Motor Company). Wanshu He (UMN) assisted in the laboratory. We thank the anonymous reviewers for their insight and helpful suggestions.