Chapter 18 - Meteorology and Air Pollution

Abstract

This chapter focuses on the transport mechanism of the pollutants through the atmosphere. Dispersion is the process by which contaminants move through the air and a plume spreads over a large area, thus reducing the concentration of the pollutants it contains. The plume spreads both horizontally and vertically. If it is a gaseous plume, the motion of the molecules follows the laws of gaseous diffusion. The most commonly used model for the dispersion of gaseous air pollutants is the Gaussian model, in which gases dispersed in the atmosphere are assumed to exhibit ideal gas behavior. The predominant force in pollution transport is the wind; pollutants move predominantly downwind. The greatest concentration of pollutant molecules is along the plume center line. Molecules diffuse spontaneously from regions of higher concentration to regions of lower concentration. The pollutant is emitted continuously, and the emission and dispersion process is steady state. Light wind results in poor dispersion. Other conditions conducive to poor dispersion are: little lateral wind movement across the prevailing wind direction, stable meteorological conditions, resulting in limited vertical air movement, large differences between day and night air temperatures, and the trapping of cold air in valleys, resulting in stable conditions, fog, which promotes the formation of secondary pollutants and hinders the sun from warming the ground and breaking inversions, and high-pressure areas resulting in downward vertical air movement and absence of rain for washing the atmosphere.