High Volume Sampling: Errors Incurred during Passive Sample Exposure Periods

Abstract

The current Federal EPA reference method for the determination of total suspended particulate matter (TSP) in the atmosphere is the high volume method (hi-vol).¹ The hi-vol sampler is normally operated for a 24 hr period by drawing air through an 8 X 10 in. glass fiber filter at an air sampling flow rate of between 40-60 cfm. TSP samples are presently collected in this manner every 6th day (61 samples/year). Results are used to determine compliance with existing National Primary Ambient Air Quality Standards for TSP (i.e., 260 µg/m³, maximum 24 hr average, not to be exceeded more than once a year; 75 µg/m³, annual geometric mean). However, when the sampling frequency is diminished to only 61 out of a possible 365 measurements each year, the degree of certainty associated with meeting these air quality standards is also decreased.^2,3 This partial sampling schedule also introduces other sampling errors. One such error caused by the exposure of the collection filter both prior and subsequent to the desired sampling day is the subject of the following discussion.