AERMOD Dispersion Modeling of Particulate Matter Emissions From Cattle Feedyards and Cotton Gins

State Air Pollution Regulatory Agencies (SAPRAs) regulate the emission rates of Particulate Matter (PM) emitted from cattle feedyards, dairies, cotton gins, and grain elevators by permitting. The permitted allowable emission rates are determined by limiting modeled concentrations using the EPA preferred dispersion model to concentrations less than the National Ambient Air Quality Standard (NAAQS). In order to model regulated PM concentrations, an emission factor is required. In previous studies, PM emission factors were developed using concentrations measured with Federal Reference Method samplers. In this research, PM emission factors were developed using the concentration data from Tapered Element Oscillating Microbalance (TEOM) samplers.  The goal of this research was to use reverse modeling and American Meteorological Society/Environmental Protection Agency Regulatory Model Improvement Committee’s Dispersion Model (AERMOD) to generate regulated PM emission factors for cattle feedyards. TEOM concentrations for PM₁₀ were compared with the predicted downwind PM₁₀ concentrations from AERMOD for the same feedyard to find a correlation between the two. It was observed that TEOM sampler concentrations of PM₁₀ were much higher than the concentrations from co-located FRM samplers. Three corrections were made to TEOM concentration measurements based upon previous research. These corrections were (1)   TEOM vs. FRM, (2) FRM PM₁₀ pre-collector oversampling and (3) evening dust peaks. Additionally, AERMOD modeling was used to predict PM₁₀ and PM_2.5 concentrations for a hypothetical cotton gin located near Amarillo, Texas. Modeling was performed for property line distances of 50 and 100 meters and for 20, 40, and 60 bale-per-hour cotton gins.  The results were evaluated for compliance with the NAAQS at the fence line and beyond. The PM₁₀ and PM_2.5 24-hr concentrations predicted by AERMOD exceeded the NAAQS at the property lines of the cotton gins for the emission factors used.