A dramatic increase in the number of swine operations across Oklahoma over the past several years has resulted in an increasing public concern not only with water quality but also with odors generated by buildings, lagoons, and land application of swine waste products. Similar problems exist within the rest of animal agriculture. This growing odor concern has served as a major motivator in the development of the Oklahoma Dispersion Model, a Web-based tool that can be used to assess current and future atmospheric dispersion conditions for near-surface releases of gases and small particulates. Besides odors associated with animal waste products, other examples include smoke from prescribed burns, and pesticides from aerial or land application. The Model generates both graphical and text output that depict current and future conditions for atmospheric dispersion (dilution of plume) and transport direction (direction of plume movement). With such knowledge, one can better assess appropriate times for the near-surface release of gases and small particulates.
Weather data from the Oklahoma Mesonet, the state's automated near-real-time weather station network, are used to generate maps of Oklahoma showing current dispersion conditions and transport direction; these maps are updated every 15 minutes. The latest NGM (Nested Grid Model) MOS (Multiple Output Statistics) forecasts for specific sites within and surrounding Oklahoma are used to generate similar maps for dispersion conditions and transport direction valid at 3-hour increments throughout the duration of the 60-hour forecast period; these maps are updated every 12 hours.
The Oklahoma Dispersion Model utilizes a rating scheme which was developed to model both the horizontal and the vertical near-surface dispersion capability of the atmosphere. This scheme, which uses currently recognized EPA algorithms in its calculations, is based on the Turner stability classification method (classes 1-7) and, with minor modifications, results in a Dispersion Index which ranges from 2-14. The dispersion maps which are produced feature a five-color classification scheme for dispersion conditions: excellent, good, moderate, poor, and very poor. Corresponding maps for transport direction utilize a station plot of temperature, relative humidity, wind speed, and wind direction.
Since April 1998 the Oklahoma Dispersion Model has been an operational management tool on the World Wide Web. This paper will discuss details of the model itself, present examples of graphical and text output from the Web page, and show how the model can be used as an agricultural management tool for timing of near-surface releases of gases and particulates.