ATMOSPHERIC PROCESSES

The atmosphere is generally divided into 6 layers, characterized by temperature differences:


  • Boundary layer -about 1-2km above the earth surface, and generally known as the lowest part of the troposphere.
  • Troposphere- about 8-15km above earth surface; lowest depth (i.e. 8km) at the poles, and 15km at the equator.
  • Stratosphere- level just above the troposphere where ozone layer is, because the oxygen at this level abosorbs a lot of solar radiation to form ozone.
  • Mesosphere, Thermosphere and exosphere are not particulary my concern because it has ben observed that air pollution occurs mostly at the troposphere and stratosphere.

At the troposphere, pollutants tend to experience R-R-D (my acronym); that is, be washed out by Rain, removed by Reaction, or Deposited on the earth surface. On the other hand, at the stratosphere, pollutants tend to remain for longer periods, due to slow downward mixing, and their effects are noticed globally.

To better understand the dynamics of air pollution (the way pollutants move and linger and all, one needs to understand some things. What makes wind move in a certain way? What makes wind blow so hard (or so gently)? Why are some pollutant plumes (stream) so thick and nasty one day, but barely noticeable another day? The reasons may be due to a number of factors:


  1. The circulation driving forces (Hint: depends on solar radiation, earth rotation).
  2. Temperature and pressure differences (Hint: deals with adiabatic lapse rates, stability classes of air, inversion layers etcetera).
  3. The pollutant plume itself (hint: where is the plume coming from? (A point source, line source, area or volume source?) The temperature of gases exiting the stack nko? What of its density? and so on).
  4. If we have all the info about the wind properties (speed, humidity, temperature at a given height, etc) as well as the plume properties (source, temperature, density, etcetera). 

How to tie all these factors together to make practical, problem-solving sense that helps us? Answer: atmospheric modelling.
Using software based on more recent theories on air pollution dispersion (i.e Monin-Obukhov as opposed to Pasquill stability classes), you can determine the extent to which pollutants will travel, and how they will do it (and when). Software include ADMS-3 (UK-based), AERMOD (US-based).



More information can be found here:

1. HARRISON, R. "Understanding Our Environment", Cambridge: The Royal Society of Chemistry, 3rd Edition, 1999

2.Air Pollution Dispersion Terminology [online]. 2010. Available from: http://en.citizendium.org/wiki/Air_pollution_dispersion_terminology


3. Atmospheric Lapse Rate. 2010. Available from: http://en.citizendium.org/wiki/Atmospheric_lapse_rate

One link leads to another so click at your own time and interest.

4. Adiabatic Lapse Rate video from

http://www.youtube.com/watch?v=cq0zIZTnYpU

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