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United States Department of Agriculture

Agricultural Research Service

Research Project: AIR QUALITY ISSUES RELATED TO AGRICULTURAL OPERATIONS AND PROCESSES Title: A Comparison of Predicted Property Line Particulate Concentrations Using Iscst3 and Aermod

Authors
item Powell, J - TAMU-TAES
item Faulkner, W - TAMU-TAES
item Parnell, JR., C - TAMU-TAES
item Wanjura, John
item Shaw, B - TAMU-TAES

Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: July 8, 2006
Publication Date: July 31, 2006
Citation: Powell, J.J., Faulkner, W.B., Parnell, C.B., Wanjura, J.D., Shaw, B.W. 2006. A comparison of predicted property line particulate concentrations using ISCST3, AERMOD, windtrax, and austal view. In: Proceedings of the Beltwide Cotton Conferences, January 3-5, 2006, San Antonio, Texas. 2006 CDROM. p. 379-385.

Interpretive Summary: ISCST3 is currently the preferred dispersion model approved by EPA for regulatory use in estimating concentrations of particulate matter (PM) at, or beyond, the property line of stationary sources. However, as of November 9, 2006, EPA will begin the process of transitioning from ISCST3 to AERMOD as the dispersion model of choice to predict PM concentrations downwind of stationary sources. AERMOD is considered to be a better model on the basis that AERMOD more accurately characterizes the planetary boundary layer. AERMOD requires much more extensive meteorological data inputs than ISCST3. The differences in the required meteorological data inputs of the two models results in different downwind concentration predictions between the two models. The work presented in this manuscript describes the process used to estimate concentrations downwind of a Texas cotton gin using both ISCST3 and AERMOD. The same facility layout and particulate matter emission rates were used in both models to estimate the downwind concentrations. On average, AERMOD predicted concentrations 1.5 times higher than ISCST3. These results present a potential problem for sources that have current air quality permits that were granted based on downwind concentration estimations using ISCST3. If the air quality permits for these sources were granted based on marginally compliant downwind concentration estimates using ISCST3, it is likely that the concentration estimates downwind of the same sources would not be in compliance with air quality standards using AERMOD.

Technical Abstract: ISCST3 has been the preferred model of the Environmental Protection Agency (EPA) to estimate concentrations of particulate matter (PM) at, or beyond, the property line of sources emitting PM such as cotton gins. The modeled concentrations can be used to limit emissions from stationary and fugitive sources. The regulatory limits of PM include limits for PM10, PM2.5, and coarse PM (PMcoarse). In November 2006, the EPA will begin transitioning to the use of AERMOD for predicting concentrations on the basis that AERMOD more accurately characterizes the planetary boundary layer. Both AERMOD and ISCST3 use a Gaussian plume model to predict concentrations, but AERMOD requires a more detailed set of meteorological inputs. Each model yields different results. The results of this work show that on average, the concentrations estimated downwind of a Texas cotton gin using AERMOD are 1.5 times higher than the downwind concentrations estimated using ISCST3. The dispersion modeling program chosen by EPA to predict property line concentrations will have a direct effect on the cotton ginning industry. Inaccurate predictions of property line concentrations for cotton gins could result in the unjust denial of air quality permits.

Last Modified: 10/30/2014
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