The transport and dispersion of air pollutants are affected by many factors, including global and regional weather patterns and local topographical conditions. For example, the prevailing wind direction in mid- latitudes (30°-60° latitude) in much of the world is from west to east; this is a significant factor in the transport of aerosols. The primary factors affecting transport and dispersion of aerosols are wind, stability, and turbulence as shown by Hall et al. The initial direction of aerosol transport is determined by the wind direction at the source, and pollution concentration from a point source is more sensitive to wind direction than any other parameter. The higher the wind speed, the lower the aerosol concentration. Changes in the wind speed with height along with stability can lead to a variety of transport patterns. Wind speed also affects the travel time from source to receptor, as a reduction of wind speed increases the travel time. For buoyant sources, plume rise depends on wind speed; the stronger the wind, the lower the altitude the plume reaches. When a temperature inversion is present, aerosols released below the inversion are trapped there and can be removed locally only by horizontal winds.
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