Air pollution spreads through a combination of transport, dispersion, and deposition.
Transport
Transport refers to the large-scale movement of pollutants carried by prevailing winds. Think of it like a river of air carrying pollutants over long distances. The direction and speed of the wind dictate the path and speed of the pollution. This can move pollutants from industrial areas to nearby cities or even across continents.
Dispersion
Dispersion is the scattering of pollutants due to atmospheric turbulence. Imagine dropping dye into water – it initially forms a concentrated blob, but quickly spreads out due to the water's movement. Similarly, turbulent air currents mix and dilute pollutants, reducing their concentration in a given area. This process is influenced by factors like wind speed, atmospheric stability (how easily air mixes), and terrain.
Deposition
Deposition is the process by which pollutants are removed from the atmosphere and settle onto the ground or water bodies. This can happen through:
- Dry deposition: Pollutants directly settling onto surfaces due to gravity or impaction (particles hitting surfaces).
- Wet deposition: Pollutants being washed out of the air by rain or snow. This process effectively cleanses the atmosphere but can also contaminate water sources and soil.
These three processes – transport, dispersion, and deposition – work together to determine the extent and impact of air pollution. For example, a factory emitting pollutants might see its immediate surroundings heavily affected (high concentration due to less dispersion), while downwind areas experience a diluted but still significant impact due to transport and eventual deposition.
