Air Pollution Dispersion Terminology - Air Pollutant Emission

Air Pollutant Emission

The types of air pollutant emission sources are commonly characterized as either point, line, area or volume sources:

• Point source — A point source is a single, identifiable source of air pollutant emissions (for example, the emissions from a combustion furnace flue gas stack). Point sources are also characterized as being either elevated or at ground-level. A point source has no geometric dimensions.

• Line sources — A line source is one-dimensional source of air pollutant emissions (for example, the emissions from the vehicular traffic on a roadway).

• Area source — An area source is a two-dimensional source of diffuse air pollutant emissions (for example, the emissions from a forest fire, a landfill or the evaporated vapors from a large spill of volatile liquid).

• Volume source — A volume source is a three-dimensional source of diffuse air pollutant emissions. Essentially, it is an area source with a third (height) dimension (for example, the fugitive gaseous emissions from piping flanges, valves and other equipment at various heights within industrial facilities such as oil refineries and petrochemical plants). Another example would be the emissions from an automobile paint shop with multiple roof vents or multiple open windows.

Other air pollutant emission source characterizations are:

• Sources may be characterized as either stationary or mobile. Flue gas stacks are examples of stationary sources and busses are examples of mobile sources.

• Sources may be characterized as either urban or rural because urban areas constitute a so-called heat island and the heat rising from an urban area causes the atmosphere above an urban area to be more turbulent than the atmosphere above a rural area.

• Sources may be characterized by their elevation relative to the ground as either surface or ground-level, near surface or elevated sources.

• Sources may also be characterized by their time duration:
  • puff or intermittent: short term sources (for example, many accidental emission releases are short term puffs)
  • continuous: a long term source (for example, most flue gas stack emissions are continuous)