Particulate Matter Sampler Errors Due to the Interaction of Particle Size and Sampler Performance Characteristics: Background and Theory

Abstract

The National Ambient Air Quality Standards (NAAQS) for particulate matter (PM), in terms of PM10 and PM2.5, are ambient air concentration limits set by the EPA that should not be exceeded. Further, state air pollution regulatory agencies (SAPRAs) utilize the NAAQS to regulate criteria pollutants emitted by industries by applying the NAAQS as a property-line concentration limit. The primary NAAQS are health-based standards; therefore, an exceedance implies that it is likely that there will be adverse health effects for the public. Prior to and since the inclusion of PM10 and PM2.5 into the EPA's regulation guidelines, numerous journal articles and technical references have been written to discuss the epidemiological effects, trends, regulations, methods of determining PM10 and PM2.5, etc. A common trend among many of these publications is the use of samplers to collect information on PM10 and PM2.5. Often, the sampler data are assumed to be an accurate measure of PM10 and PM2.5. The fact is that issues such as sampler uncertainties, environmental conditions, and characteristics of the material that the sampler is measuring must be incorporated for accurate sampler measurements. The purpose of this article is to provide the background and theory associated with particle size distribution (PSD) characteristics of the material in the air that is being sampled, sampler performance characteristics, the interaction between these two characteristics, and the effect of this interaction on the regulatory process. The results show that if the mass median diameter (MMD) of the PM to which the sampler is exposed is smaller than the cutpoint of the sampler, then under-sampling occurs. If the MMD of the PM is greater than the cutpoint of the sampler, then over-sampling occurs. The information presented in this article will be utilized in a series of articles dealing with the errors associated with particulate matter measurements.