|Some air pollution
problems are limited to the local area where pollution is emitted. Other air quality problems spread to cover cities or regions of the
country. Emissions of some pollutants
from anywhere on earth can contribute to a global problem. While some pollutants can be neatly
characterized as contributors to local, regional, or global problems, many
pollutants are important on multiple spatial scales. Explaining the factors that control the
spatial extent of a pollutant requires understanding the emissions,
transport, and chemistry of a pollutant.
primarily emitted pollutants are almost always highest very close to their
emissions source (for primary pollutants).
The figure illustrates the typical drop-off in concentrations
from an emissions source as distance increases from the source. Pollution concentrations start very high,
but are diluted by the atmosphere in the first few hundred feet from a source
as they are transported and dispersed.