In dispersion modeling, what does "e" typically represent in equations?

In dispersion modeling, "e" typically represents the surface roughness, denoted as a measure of the height of surface obstacles in the influence of wind flow above a certain height. Surface roughness impacts how wind flows over different terrains and can significantly affect how pollutants disperse in the atmosphere.

Understanding surface roughness is crucial for accurate dispersion modeling because it influences the turbulence of the air. Areas with higher roughness, such as urban environments with buildings, create more turbulence, leading to better mixes of pollutants. Conversely, smoother areas, like lakes or flat fields, allow for more laminar flow, which can impact dispersion patterns.

Differentiating between air density, temperature gradient, and humidity levels is essential for various aspects of atmospheric modeling, but these factors do not represent "e" in the context of surface roughness. Air density relates more closely to the mass of air in a given volume, which affects buoyancy and pollutant travel, while temperature gradients influence stability and vertical mixing. Humidity levels pertain to water vapor in the air and its influence on air density and chemical reactions, but again, they are not represented by "e" in this framework.