The processes governing the transport and diffusion of pollutants are numerous and of complexity that it would be impossible to describe them without the use of mathematical models. There exist innumerable, sometimes very diverse, mathematical models of atmospheric pollutant diffusion that may be utilized for the aforementioned purposes. Of the Eulerian models, box models constitute the simplest mathematical approach, since they ignore the spatial structure of phenomena. The pollutant present in the box originates from internal sources or from external contributions transported by wind or flows through the summit as a consequence of variations in height of the box itself, which generally coincides with the mixed layer height. Analytical solutions explicitly take into account all the parameters of a problem, so that their influence can be reliably investigated, and it is easy to obtain the asymptotic behavior of the solution, which is usually difficult to generate through numerical calculations.