Air Quality Modelling

Back to Contents

What is Air Quality Modelling

Modelling is a general term which, amongst other things, is applied to a process that involves the use of specialist software that can predict outcomes based on input data. In relation to air quality, modelling software can predict how, for example, the emissions from a factory will disperse from the point of release. In this way it is possible to ascertain what the level of a specific pollutant will be at different locations, such as at a housing estate two miles to the east of a factory where pollutants were being released. In the same way, dispersion modelling software can predict how the exhaust emissions from vehicles on a road will disperse. Therefore we can see what the levels of specific pollutants will be, for example, at the facades of the houses adjacent to the road.

In order to carry out air quality modelling it is first necessary to build the model. This involves populating the software with information on everything from the factories in the area, including emissions information, traffic flows and speeds, geographical information such as maps that illustrate the major roads and relevant receptor locations such as housing estates and historical weather information. The software is then able to produce a plot of the required area, overlaid on which will be a set of contours that relate to the different concentrations of the pollutant being modelled. This can then be used to ascertain if there are any locations within the area that are in excess of the appropriate National Air Quality Standard.

View the dispersion model output for Riby Square / Cleethorpe Road (2005).

Dispersion Model Output - Riby Square / Cleethorpe Road

Building and applying dispersion models is not a quick process and can take several months, or even years, to develop, depending on the extent of the area and the number of polluting sources being modelled.

Why is it important?

Air quality modelling is crucial as it can provide information about pollution levels in present and future years, and at locations where it would be impractical to carry out monitoring given the size of the monitoring equipment used. The former is very important since the National Air Quality Standards have to be achieved by various different years up to 2010 and therefore the software can give us an idea as to whether or not the standards are likely to be achieved on target. The ability to predict air quality in certain inaccessible locations is also extremely important as, for example, the levels of pollution generated by vehicles on a busy road will decrease very quickly with increasing distance from the road. Therefore the level of pollution measured at the curb by a real time monitoring station could be quite different from the actual level of pollution at the facade of the adjacent house which is further away.

Dispersion models can provide information on pollution levels both in a wide area and at specific locations. However, monitoring equipment can only supply information at the location where the equipment is placed and is therefore limited as pollution levels at two very near by locations could be quite different depending on the circumstances. In addition, dispersion modelling can also be used to demonstrate the possible impacts on air quality due to planned developments, such as supermarkets or factories.

Is it accurate?

Unfortunately dispersion models are only as accurate as the data used to build them, such as the traffic flows and vehicle make up. Therefore it is necessary to verify the developed models with measured data from a real time air quality monitoring station. Discrepancies between modelled and measured data can then be overcome by adjusting the model appropriately or by incorporating a correction factor.

Does the Council carry out Air Quality Modelling?

In the past the Council has employed specialist consultants to carry out this essential work, as above. However a recent successful bid for Government funding has enabled the Council to purchase its own air quality modelling software. From now on this work will be carried out in house and at significantly less cost than employing external consultancy services.