Application of the National Ambient Air Quality Standards (NAAQS) in Urban Versus Rural Environments

The US Environmental Protection Agency is currently assessing the need for a National Ambient Air Quality Standard for the coarse fraction of particulate material (PMCF), specifically, the fraction of particulate matter between 2.5 and 10 μm in aerodynamic equivalent diameter. EPA is primarily relying on epidemiological studies that examine the possible health effects of PMCF to reach a decision about developing a coarse particulate matter standard. These epidemiological studies utilize data from size-selective PM samplers to estimate the study population’s exposure to PM10, PM2.5, and PMCF. Epidemiological studies typically focus on urban populations in order to obtain sufficient sample size and increase statistical certainty of study findings. This focus on urban environments has resulted in a lack of studies evaluating the effect of coarse particulate matter in rural environments. There are a number of key differences between the urban and rural environments in the United States that can lead to mistakes in applying data from urban studies to rural environments. These include differences in particle sources, affecting particle size distribution and composition, differences in the concentration of gaseous co-pollutants, and differences in PM sampler performance in the two environments. It is our contention that these differences between the urban and rural environment are significant and that the epidemiological studies cited by EPA rely on data that are not representative of rural environments, raising concerns that the implementation of a PMCF standard in rural environments will impose an unfair and unwarranted regulatory burden on the businesses and citizens in these areas.