True or False: Denser-than-air COTAs can alter the downwind distance to a concentration level compared to a passive atmospheric dispersion model.

The statement is true because denser-than-air chemical released in the atmosphere, such as dense gas or heavier-than-air contaminants, will behave differently than lighter, buoyant gases. This behavior impacts how far downwind the chemical will travel before reaching a certain concentration level.

In passive dispersion models, the assumption is often made that all materials are neutrally buoyant or follow a similar path based solely on wind speed and atmospheric stability. However, denser-than-air contaminants tend to sink and accumulate in lower areas, like valleys or depressions, which can extend the distance downwind at which specific concentration levels are reached compared to what those models would predict.

Furthermore, the physical characteristics of the pollutants, the surrounding terrain, and the meteorological conditions that contribute to dispersion will vary based on the density of the material. Therefore, utilizing a model that specifically accounts for the behavior of denser-than-air chemicals adds complexity not accounted for in simpler passive models. This results in different predicted impacts on the dispersion and distance from the source before reaching a particular concentration level.