A SIMULATED APPROACH TO ESTIMATING PM10 AND PM2.5 CONCENTRATIONS DOWNWIND FROM COTTON GINS

Cotton gins are required to obtain operating permits from state air pollution regulatory agencies (SAPRA), which regulate the amount of particulate matter that can be emitted. Industrial Source Complex Short Term version 3 (ISCST3) is the Gaussian dispersion model currently used by some SAPRAs to predict downwind concentrations used in the regulatory process in the absence of field sampling data. The maximum ambient concentrations for PM10 and PM(2.5) are set by the National Ambient Air Quality Standard (NAAQS) at 150 microgram/m3 and 65 microgram/m3 (24 h average), respectively. Some SAPRAs use the NAAQS concentrations as property line concentrations for regulatory purposes. This article reports the results of a unique approach to estimating downwind PM10 and PM(2.5) concentrations using Monte Carlo simulation, the Gaussian dispersion equation, the Hino power law, and a particle size distribution that characterizes the dust typically emitted from cotton gin exhausts. These results were then compared to a 10 min concentration (C10) and the concentrations that would be measured by an FRM PM10 and PM(2.5) sampler. The total suspended particulate (TSP) emission rate, particle size distributions, and sampler performance characteristics were assigned to triangular distributions to simulate the real-world operation of the gin and sampling systems. The TSP emission factor given in AP-42 for cotton gins was used to derive the PM mass emission rate from a 40 bale/h plant. The Gaussian equation was used to model the ambient TSP concentration downwind from the gin. The performance characteristics for the PM10 and PM(2.5) samplers were then used to predict what the measured concentration would be for two PSD conditions. The first PSD assumption was that the mass median diameter (MMD) and geometric standard deviation (GSD) were constant at 12 micrometer and 2, respectively, and the second scenario assigned a triangular distribution to the MMD and GSD of (15, 20, 25) micrometer and (1.8, 2.0, 2.2), respectively. The results show that the PM(2.5) fraction of the dust emitted under either PSD condition was negligible when compared to the NAAQS for PM(2.5) of 65 microgram/m3. The results also demonstrate that correcting for wind direction changes within the hour using the power law reduces the ambient concentration by a factor of 2.45.