| Atmospheric aerosols are comprised of inorganic salts, carbonaceous material, trace metals, crustal materials, and water, and impacts health, visibility, and climate. Regulations promulgated by the EPA for fine particles less than 2.5 um in diameter (PM2.5) have raised the need for evaluation of emission control strategies to determine effective means by which the mass concentration of these particles can be reduced.; In the eastern U.S., inorganic species account for approximately half of the PM2.5 mass, and thus the characterization and interaction of inorganic components has been a large component of this work. To measure the chemical composition of inorganic PM2.5 in the Western Pennsylvania region, a filter-based method was employed daily from July 2001 to July 2002 during the Pittsburgh Air Quality Study (PAQS). This data set was used to evaluate measurements by newer, semi-continuous technologies providing high-time resolution measurements of inorganic ions, and to provide reference measurements for correction of analytical biases in the new instruments.; Using the corrected high-time resolution measurements, a thermodynamic model, GFEMN, was used to simulate the partitioning of PM2.5 nitrate aerosol and nitric acid. Model results were evaluated using independent, time-resolved measurements of aerosol nitrate. The mean observed concentration in July was 0.6 mug/m3 and 2.1 mug/m3 in January. Model predictions were in agreement with the observations within 0.5 mug/m 3 on average, with measurement uncertainties often accounting for these discrepancies. The simulations were run assuming particles were liquid in July for all relative humidities (RHs) and solid below 60% RH in January. For both seasons the assumed physical state did not influence considerably the overall agreement with observations. The assumption of particle mixing state did appear to influence model error, however- assuming that particles were externally mixed during low RH periods in July improved agreement significantly. The exceptional sensitivity of predicted aerosol nitrate to ammonia in Western Pennsylvania suggests that reductions in PM2.5 may be assisted by reductions in ammonia emissions.; Current strategies for reducing PM2.5 mass concentrations target reducing SO2 to reduce sulfate, but in such a case more ammonium nitrate may form when nitric acid is present. Large-scale chemical transport models suffer from uncertainties associated with emission inventories. (Abstract shortened by UMI.)... |
