Particulate Matter Sampler Errors Due to the Interaction of Particle Size and Sampler Performance Characteristics: Ambient PM2.5 Samplers

Abstract

The National Ambient Air Quality Standards (NAAQS) for particulate matter (PM) in terms of PM2.5 are ambient air concentration limits set by the EPA to protect public health and well-being. Further, some state air pollution regulatory agencies (SAPRAs) utilize the NAAQS to regulate criteria pollutants emitted by industries by applying the NAAQS as property-line concentration limits. Prior to and since the inclusion of the PM2.5 standard, numerous journal articles and technical references have been written to discuss the epidemiological effects, trends, regulation, and methods of determining PM2.5. A common trend among many of these publications is the use of samplers to collect PM2.5 concentration data. Often, the sampler data are assumed to be accurate concentration measures of 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 focus of this article is on the errors associated with particle size distribution (PSD) characteristics of the material in the air that is being sampled, the PM2.5 sampler performance characteristics, the interaction between these two characteristics, and the effect of this interaction on the regulatory process. Theoretical simulations were conducted to determine the range of errors associated with this interaction for the PM2.5 ambient air samplers. Results from the PM2.5 simulations indicated that a source emitting PM characterized by a mass median diameter (MMD) of 20 m and a geometric standard deviation (GSD) of 1.5 could be forced to comply with a PM2.5 standard that is 14 times more stringent than that required for a source emitting PM characterized by an MMD of 10 m and a GSD of 1.5, and 59 times more stringent than that required for a source emitting PM characterized by an MMD of 5.7 m and a GSD of 1.5. Therefore, in order to achieve equal regulation among differing industries, PM2.5 measurements must be based on true concentration measurements.