Historic PM_2.5/PM₁₀ Concentrations in the Southeastern United States-Potential Implications of the Revised...

This report summarizes a PM_2.5/PM₁₀ particulate matter data set consisting of 861 PM_2.5/PM₁₀ sample pairs collected with dichotomous samplers by the Tennessee Valley Authority (TVA) from 1982 to 1991. Eight monitoring stations, ranging from urban-industrial to rural-background, were operated across three east-central U.S. states. Annual average PM_2.5 concentrations ranged from 12.6 to 21.3 micrograms per cubic meter (μg/m³), with an overall mean of 15.7 μg/m³. Likewise, annual average PM₁₀ concentrations ranged from 17.8 to 33.7 μg/m³, with an overall mean of 23.7 μg/m³. High summer-low winter seasonality was evident, particularly for PM_2.5, with the highest monthly PM_2.5 and PM₁₀ concentrations in August (26.4 and 37.5 μg/m³, respectively) and the lowest in February (9.9 and 15.3 μg/m³, respectively). A strong association (r² = 0.84) was found between PM and PM mass with PM mass contributing, on average, 67% of PM₁₀ mass. Applying TVA's PM_{2 5}/PM₁₀ ratio to recent (1993-1995) regional high-volume PM₁₀ Aerometric Information Retrieval System (AIRS) data for the east-central United States suggests that as many as 80% of monitored counties would have equaled or exceeded the level of the new annual PM_2.5 metric of 15 μg/m³. A decline in average PM_2.5 mass on the order of 3-5 μg/m³ from 1982 through 1991 is also suggested. Daily PM_{2 5} mass appears to be reasonably well associated (r = 0.47) with maximum hourly ozone during the warmer months (spring through fall). Sulfate compounds comprise a major portion of the measured PM_{2 5} mass, with that fraction being highest in the summer months. Viewed collectively, these data suggest that although compliance with the annual and 24-hr PM and 24-hr PM metrics should prove readily attainable, the annual PM_2.5 metric will present a major regulatory management challenge for much of the east-central United States.