Air Quality monitoring of nitrogen dioxide (NO2) for proposed residential development

Our client instructed us to conduct an air quality assessment as part of the planning application for a 5,000-unit residential development in South East England. We monitored the main traffic-related pollutant, nitrogen dioxide (NO₂), to characterise baseline concentrations and ensure the model used in the assessment is performing well, given that the site was situated near a busy road.

Challenge

For the planning application, we conducted detailed dispersion modelling of traffic-related emissions to assess the impact of the scheme on the surrounding area and determine the suitability of air quality at the site for its proposed residential use.

To facilitate this modelling, we required existing background concentrations at the site and surrounding road network to establish a baseline concentration and ensure the accuracy of the model used.

Although the local authority monitors NO₂ at several locations, these sites were not fully representative of the conditions at the site. Without representative data, we would have needed to make several conservative assumptions, potentially resulting in unnecessary recommendations for mitigation measures.

Solution

To ensure that we avoided recommending unnecessary mitigation measures, we conducted a site-specific six-month monitoring survey at 18 locations in and around the Application Site using diffusion tubes. Diffusion tubes offer a fairly low-cost monitoring method, making them beneficial for large sites as they allow monitoring to cover a wide area. We measured concentrations across the site along a transect away from the busy road.

The results revealed that concentrations at the proposed residential units closest to the road were well below the air quality limit values, confirming the site's suitability for its proposed residential use. We also measured concentrations on smaller roads surrounding the site and compared the results with modelled concentrations to verify the accuracy of the model.

This validation process improved our confidence in the modelling undertaken to assess the scheme's impact on the surrounding area.