Air pollution dispersion terminology

Air pollution dispersion terminology includes the words and technical terms that have a special meaning to those who work in the field of air pollution dispersion modeling. Governmental environmental protection agencies (local, state, province and national) of many countries have also adopted and used much of the terminology in their laws and regulations regarding air pollution control.

Some of the words and technical terms in Air pollution dispersion terminology quite often have other special meanings when used in fields of activity other than air pollution dispersion modeling.

Contents

Air pollution emission plumes

There are three primary types of air pollution emission plumes:

Air pollution dispersion models

There are five types of air pollution dispersion models, as well as some hybrids of the five types:[1]

Air pollutant emission

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

Other air pollutant emission source characterizations are:

Characterization of atmospheric turbulence

The amount of turbulence in the ambient atmosphere has a major effect on the dispersion of air pollution plumes because turbulence increases the entrainment and mixing of unpolluted air into the plume and thereby acts to reduce the concentration of pollutants in the plume (i.e., enhances the plume dispersion). It is therefore important to categorize the amount of atmospheric turbulence present at any given time.

The Pasquill atmospheric stability classes

The oldest and, for a great many years, the most commonly used method of categorizing the amount of atmospheric turbulence present was the method developed by Pasquill in 1961.[10] He categorized the atmospheric turbulence into six stability classes named A, B, C, D, E and F with class A being the most unstable or most turbulent class, and class F the most stable or least turbulent class. Table 1 lists the six classes and Table 2 provides the meteorological conditions that define each class.

For air dispersion modeling exercises, the conditions of dual stability classes like A – B, B – C and C – D can be considered as B, C and D respectively.

Table 1: The Pasquill stability classes
Stability class Definition   Stability class Definition
A very unstable   D neutral
B unstable   E slightly stable
C slightly unstable   F stable
Table 2: Meteorological conditions that define the Pasquill stability classes
Surface windspeed Daytime incoming solar radiation Nighttime cloud cover
m/s mi/h Strong Moderate Slight > 50% < 50%
< 2 < 5 A A – B B E F
2 – 3 5 – 7 A – B B C E F
3 – 5 7 – 11 B B – C C D E
5 – 6 11 – 13 C C – D D D D
> 6 > 13 C D D D D
Note: Class D applies to heavily overcast skies, at any windspeed day or night

Historical stability class data, known as the Stability Array (STAR) data, for sites within the USA can be purchased from the National Climatic Data Center (NCDC).[11]

Advanced methods of categorizing atmospheric turbulence

Many of the more advanced air pollution dispersion models do not categorize atmospheric turbulence by using the simple meteorological parameters commonly used in defining the six Pasquill classes as shown in Table 2. The more advanced models use some form of Monin-Obukhov similarity theory.

For example, the US EPA's most advanced model, AERMOD,[12] no longer uses the Pasquill stability classes to categorize atmospheric turbulence. Instead, it uses the surface roughness length and the Monin-Obukhov length.

As another example, the United Kingdom's most advanced model, ADMS 3,[13] uses the Monin-Obukhov length, the boundary layer height and the windspeed to categorize the atmospheric turbulence.

The detailed explanation of the mathematical formulation for the turbulence categorization methods used in AERMOD, ADMS 3 and other advanced air pollution dispersion models is very complex and beyond the scope of this article. More detailed explanations are available on the Internet.[12][13]

Miscellaneous other terminology

(Work on this section is continuously in progress)

See also

Air pollution dispersion models

Others

References

  1. ^ List of atmospheric dispersion models
  2. ^ Air Pollution Dispersion: Ventilation Factor by Dr. Nolan Atkins, Lyndon State College
  3. ^ Bosanquet, C.H. and Pearson, J.L. (1936).The spread of smoke and gases from chimney, Trans. Faraday Soc., 32:1249.
  4. ^ Atmospheric Dispersion Modeling
  5. ^ a b c Beychok, Milton R. (2005). Fundamentals Of Stack Gas Dispersion (4th Edition ed.). author-published. ISBN 0-9644588-0-2.  (Chapter 8, page 124)
  6. ^ a b Features of Dispersion Models publication of the European Union Joint Research Centre (JRC)
  7. ^ DEGADIS Technical Manual and User's Guide (US EPA's download website)
  8. ^ SLAB User's Manual
  9. ^ HEGADIS Technical Reference Manual
  10. ^ Pasquill, F. (1961). The estimation of the dispersion of windborne material, The Meteorological Magazine, vol 90, No. 1063, pp 33-49.
  11. ^ NCDC website for ordering stability array data
  12. ^ a b AERMOD:Description of Model Formulation
  13. ^ a b Model developer's description of ADMS 3 (click on "next" for more description)

Further reading

External links