Introduction

 

Obviously it is better to minimise or eliminate the production of pollutants at source but if they have to be produced it is necessary to ensure that the effects of pollution are minimised. A common approach to this has been to put the pollutant into the atmosphere so as to ensure that it is diluted and dispersed to a sufficiently low concentration before it contacts a sensitive receptor.

This approach was the first attempt at air pollution control and today it still plays an important role, even when complex end of pipe solutions are involved. This unit and Unit 5, Modelling, look at the way in which air pollutants are dispersed and the way in which our knowledge of air pollutant dispersal can be used to predict the effects of pollution.

Some mathematics is involved and certain calculation skills will be required as follows:

  1. A basic ability to deal with rearrangement of formulae.
    2.
  2. An ability to deal with exponents
    3.
  3. An understanding of the use of natural and decimal logarithms.
    4.
  4. Either ability in calculus or a willingness to believe what is said when differentials are dealt with.
    5.
  5. An ability to use a scientific calculator and a computer with a modern spreadsheet package.(alternatively just the computer and spreadsheet).
    6.

If you do not have the above pre-knowledge then you will not benefit to the full from this Unit. However the modelling can be approached as a "black box" and investigating the computations should still prove beneficial.

The simpler models of air pollution that currently form the basis of the more complex models that are used to predict pollution patterns on both a global and local basis. Although monitoring appears to be the most accurate way to measure the environmental effects of pollution there is tremendous sampling variability in the environment. Moreover it is not financially feasible to continually invest in the infinite array of pollution measuring devices. Models produce no less a true view of the environment than monitoring. It is in intelligent interpretation of models and monitoring that we become closer to a useful interpretation of the situation, not a blind acceptance of either.
As you read this unit and continue your reading widely you should be aware that this subject has both a long and broad history. Moreover the authors of textbooks have often been willing to mix and match the appropriate work of a variety of authors written over long periods of time. Sometimes this is for good scientific reasons but often for the convenience of the author or for the benefit of the target audience.

There is still a great deal of controversy over which methods should be used to describe the behaviour of air pollutants as they disperse in the atmosphere.

Another conclusion which you might reach is that the methods which work adequately whilst remaining as easy to use as possible, have been the ones which are commonly used. The techniques requiring advanced mathematics and powerful computing have been the ones, which have remained in the hands of academics. This is changing with the advent of cheaper, very powerful computers and software, based on the more complex theories but easy to operate are becoming widespread. The problem with such models is that they, inevitably, have a number of default values built into the system to ease the load of the operator when a part of the required data is missing. A failure to understand the limitations of the use of such default values will result in the familiar term that often applies to computers, rubbish in-rubbish out.