Explanation of Modelling
The air that we breathe is contaminated with air pollutants from sources such as the motor vehicle, industrial processes and building heating systems. Some pollutants have adverse health effects. The UK Government has devised a set of future objectives for these pollutants which must be met. These are contained within the Air Quality Strategy (AQS). Local authorities have been given responsibility to put the AQS into practise.
The likelihood of everywhere in the London Borough of Ealing meeting the AQS objectives is dependent upon measures taken nationally and locally. National measures, for example, using catalytic converters in new cars, are predicted to reduce pollutant concentrations throughout the UK. Where such measures fail to reduce them far enough, however, local action will be necessary to make up the shortfall. Predictions of the existence of such shortfalls require the use of predictive models.
What is a model?
Modelling is a generic term which we use here to describe the calculation of the quantity of harmful pollutants emitted into the atmosphere and how they are transported, diluted and transformed through chemical reactions. These calculations result in the prediction of pollutant concentrations in locations where the population can be exposed i.e. where they can be breathed in. These calculations can be undertaken for the present day as well as for the future. These can then be compared with the AQS objectives to see how well or how badly we are doing.
The NO2 and PM10 Objectives
The AQS has set objectives for two important air pollutants; nitrogen dioxide (NO2) and small particles or dust (PM10).
This model gives predictions of average NO2 and PM10 for a yearly period. Since 2005 this value has to be below 40 micro-grammes per metre cubed (µg m-3) for both pollutants. If pollution is below this level then it meets the AQS. However where this level is exceeded and people can breathe the pollution it is the duty of Council to try to reduce it. The steps that the Council can take are included in its Air Quality Action Plan.
The model also gives predictions for PM10. The daily mean objective (from 2005) is 35 days. This means that where the number of days exceeding the guideline standard exceeds 35 the objective is exceeded and where it is less it is vice versa.
Why is weather important?
Meteorology or Met., is used by modellers and others to describe the weather, Meteorology is very important when predicting concentrations of air pollutants. For example in certain conditions say, when the wind blows strongly, air pollutants are blown away and the result is an improvement in air quality.
It is however impossible to predict the weather for whole years into the future, most weather forecasts are only given for at most predictions 5 days ahead. To overcome this we have to make future predictions based on the weather that has already happened, and currently we use 2003 for this purpose.
Why use the weather for 2003?
The predictions made using this are considered to represent a scenario that is consistent with a precautionary approach; this means that concentrations are realistically higher based on recent air pollution measurements.
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