June 2009
Front Matter
Training
32
Formation, Destruction, Transport (1 of 2)
While some pollutants can be neatly characterized as contributors to local, regional, or global problems, many pollutants are important on multiple spatial scales.
Conceptual depiction of
transport scales.
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.
Concentrations of 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.