The impact of emissions to air on human health and the wider environment requires to be quantified in planning applications, EIAs, PPC applications, Local Air Quality Management (LAQM) and a number of other situations for a range of emissions sources. The impact must be compared with Air Quality Standards and guidelines and other environmental assessment levels (EALs). Ambient monitoring can quantify ground level concentrations of pollutants from current emissions but this can be expensive and the location of maximum impact is not always known. Dispersion modelling can be used in order to plan monitoring surveys by predicting the location of impact from a particular source or group of sources. It is the recognised technique for predicting the impact of proposed developments or future operating scenarios.

BMT Cordah Ltd has an established Air Quality Unit with a team of experienced staff in the field of air quality management. The Air Quality Unit has particular technical and practical expertise in the application of state-of-the-art dispersion modelling software systems including the UK developed ADMS suite of models and the US EPA ISC/AERMOD models. Dispersion modelling studies are undertaken to assess the short and long term impacts of emissions to air of controlled and accidental releases from a variety of industrial, traffic, domestic and commercial sources. Concentration and deposition contours can be presented on digital map data and GIS analysis can be carried out, for example, to calculate the population affected by a particular exposure concentration. Modelling can be used to quickly check stack height calculations and assess the environmental performance of a number of proposed operational scenarios or abatement techniques. Such techniques are used frequently in the assessment of BAT for IPPC applications.