Dense Gas models, such as SLAB and DEGADIS, have existed for many years and are used to model such phenomena as material releases due to the collapse of a tank storing a volatile liquid, the crash of a tanker truck, and jet release from valve ruptures. These models were originally developed to have low computational requirements. As such, most Dense Gas models are so-called 1-D models that capture downstream dispersion of a denser than air cloud. Dense Gas models handle the cloud thermodynamics in some form. For example, SLAB captures changes in cloud temperature and turbulent mixing due to liquid droplet formation and evaporation. Although relatively simple, these models may represent significant improvements to current spray drift applied models through improved thermodynamics.
Here, we evaluate spray cloud thermodynamics in an effort to improve spray drift models. We compare pesticide drift models to dense gas models over a range of application rates, droplet size distributions, and ambient meteorological conditions for simple spray configurations (i.e., one nozzle with zero crosswind). Evaporative loss and fraction of applied to the ground surface as a function of downwind distance from the source are presented.