High volume sampling - Errors incurred during passive sample exposure periods

The high volume (hi-vol) method is the current federal EPA reference method for determining total suspended particulate matter (TSP) in the atmosphere. The hi-vol sampler is normally operated for a 24-hr period and TSP samples are collected every sixth day so that the degree of certainty associated with meeting the air quality standards is decreased. The paper discusses the error caused by the exposure of the collection filter both prior and subsequent to the desired sampling day. The resulting deposition of particles caused by exposing the filter paper for six days prior to sampling is summarized and discussed. A hi-vol filter may sometimes be exposed for up to five days after sampling ends, in addition to the five days before sampling begins. It is concluded that installing the hi-vol filter prior to the commencement of sampling and leaving the filter exposed subsequent to the completion of sampling introduces potentially large errors in any given TSP measurement. Factors affecting the magnitude of the error are identified.