PARTICULATE MATTER SAMPLER ERRORS DUE TO THE INTERACTION OF PARTICLE SIZE AND SAMPLER PERFORMANCE CHARACTERISTICS: PM10 AND PM2.5 AMBIENT AIR SAMPLERS

Abstract

Agricultural operations across the United States are encountering difficulties complying with the current air pollution regulations for particulate matter (PM). The National Ambient Air Quality Standards (NAAQS) for PM in terms of PM10 and PM2.5 are ambient air concentration limits set by EPA that should not be exceeded. Further, some State Air Pollution Regulatory Agencies (SAPRA’s) utilize the NAAQS to regulate criteria pollutants emitted by industries by applying the NAAQS as property line concentration limits. The primary NAAQSs are health-based standards and 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 the PM10 standard and prior to and since the proposal of the PM2.5 standard, numerous journal articles and technical references have been written to discuss the epidemiological effects, trends, regulation, 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 is assumed to be accurate measures of PM10 and PM2.5. The fact is that issues such as sampler uncertainties, environmental conditions, and material characteristics for which the sampler is measuring must be incorporated for accurate sampler measurements. The focus of this manuscript is on the errors 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. Theoretical simulations were conducted to determine the range of errors associated with this interaction for the PM10 and PM2.5 ambient air samplers. Results from the PM10 simulations indicated that a source emitting PM characterized by a mass median diameter (MMD) of 20 µm and a geometric standard deviation (GSD) of 1.5 could be forced to comply with a PM10 standard that is 3.2 times more stringent than that required for a source emitting PM characterized by a MMD of 10 µm and a GSD of 1.5. Results from the PM2.5 simulations indicated that a source emitting PM characterized by a mass median diameter (MMD) of 20 µm 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 a MMD of 10 µm and a GSD of 1.5. Therefore, in order to achieve equal regulation among differing industries, PM10 and PM2.5 measurements MUST be based on true concentration measurements.