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United States Department of Agriculture

Agricultural Research Service

Title: The Fritz-Texas A&M dispersion model development and comparative modeling with ISC3 and AERMOD

item Fritz, Bradley - Brad
item Shaw, Bryan
item Parnell, Calvin

Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/10/2003
Publication Date: 1/10/2003
Citation: Fritz, B.K., Shaw, B.W., Parnell, C.B. 2003. The Fritz-Texas A&M dispersion model development and comparative modeling with ISC3 and AERMOD. Proceedings of the Beltwide Cotton Conference, January 6-10, 2003, Nashville, TN. CDROM.

Interpretive Summary: Small agricultural businesses, including cotton gins, feed mills and grain elevators, must demonstrate that normal operations do not create off-site airborne concentrations of particulates exceeding the maximum levels established by the United States Environmental Protection Agency. Demonstrations of compliance, usually through mathematical dispersion models, are required for businesses to receive a permit allowing operation, and may be required at anytime as proof of continued compliance. Current dispersion models estimate unrealistically high downwind particulate concentrations. The newly developed Fritz-Texas A&M (FTAM) dispersion model estimates particulate concentrations that more closely represent real-world expected values. The major improvement made by FTAM is the methodology used to account for variations in wind speed and direction. Use of the FTAM for demonstrating source compliance will ensure fair regulation of agricultural businesses by state environmental agencies and safe levels of airborne particulate.

Technical Abstract: The air pollution regulatory process involves the permitting of sources of regulated pollutants. Part of the permit process requires sources to demonstrate that the National Ambient Air Quality Standards (NAAQS) are not exceeded as a result of pollutant release. While ambient air sampling may be used to demonstrate compliance with the NAAQS, a source's right to operate is becoming increasingly dependent primarily on dispersion modeling results. Currently used Gaussian-based dispersion models do not adequately account for pollutant dispersion resulting from sub-hourly variations in wind speed and direction. This can result in over-estimates of downwind concentration, which may result in costly additional control measures or operating permit being denied. Low elevation releases and close property line boundaries cause low-level agricultural sources, such as cotton gins, to be very sensitive to inappropriate modeling results. This research focused on the issue of developing a methodology to analyze the theoretical degree of dispersion within sub-hourly intervals. The degree of dispersion was based on small time-interval (15 second) meteorological data. Using the results of this analysis a new model that accounts for plume dispersion due to sub-hourly variation in wind speed and direction, was developed. The new model Fritz-Texas A&M (FTAM) was compared to the currently used regulatory models, ISC3 and AERMOD, using concentration predictions downwind of a source typical of a cotton gin. FTAM 24-hour concentrations were generally lower that ISC3 predicted 24-hour concentrations, and similar or slightly higher than AERMOD predicted 24-hour concentrations.

Last Modified: 08/18/2017
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