Air Quality Assessment

An Air Quality Management Area (AQMA) is an area where the local authority has determined that national air quality objectives are not being met or are at risk of not being met. Most AQMAs in the UK are designated due to exceedances of the annual mean nitrogen dioxide objective (40 micrograms per cubic metre), usually caused by road traffic emissions. Development within or near an AQMA will almost certainly require an Air Quality Assessment.

It depends on the location and scale. If the site is within or adjacent to an AQMA, or near a busy road, an AQA is very likely to be required. Many councils set traffic generation thresholds — for example, requiring an AQA if the development generates more than a specified number of vehicle movements per day. For larger developments (typically 10 or more dwellings), an air quality screening assessment or full AQA is increasingly standard even outside AQMAs.

The key pollutants assessed are nitrogen dioxide (NO2) and particulate matter (PM10 and PM2.5), as these are the pollutants most commonly associated with road traffic and most likely to exceed UK air quality objectives. Depending on the development type, other pollutants may also be relevant — sulphur dioxide and metals for industrial sources, or volatile organic compounds for certain processes. Construction dust (TSP) is assessed separately using the IAQM methodology.

A construction dust assessment evaluates the risk of dust emissions during the demolition, earthworks, construction, and trackout phases of a development. It follows the IAQM Guidance on the Assessment of Dust from Demolition and Construction (2023) and assigns a risk level (low, medium, or high) based on the scale of works and the sensitivity of nearby receptors. The assessment then specifies appropriate dust mitigation measures to be implemented through a construction management plan.

Yes, though outright refusal on air quality grounds alone is relatively uncommon for residential developments. More typically, the AQA identifies measures that can mitigate impacts to acceptable levels — electric vehicle charging points, travel plans, low-emission heating systems, or mechanical ventilation with filtration for dwellings near busy roads. However, if the assessment shows that future occupants would be exposed to unacceptable pollution levels that cannot be mitigated, refusal is possible.

Common mitigation measures include provision of electric vehicle charging infrastructure, travel plans to reduce car dependency, use of low-emission boilers and heating systems, mechanical ventilation with NOx filtration for units facing busy roads, setback distances between buildings and roads, green infrastructure such as hedging or green walls, and financial contributions towards local air quality improvement measures. The appropriate measures depend on the nature and severity of the identified impacts.

Air quality neutral is a policy requirement in London and some other areas that requires new developments to be at least 'neutral' in their air quality impact — meaning they should not increase pollution above benchmark levels. It is assessed by comparing the development's anticipated transport and building emissions against benchmark values. If the benchmarks are exceeded, mitigation measures or off-site contributions are required to achieve neutrality.

The two assessments are closely linked. The Air Quality Assessment relies on traffic flow data from the Transport Assessment to predict vehicle emissions and pollutant concentrations. Changes to the traffic assessment — such as revised trip generation rates or road layout modifications — can affect the air quality conclusions. For this reason, the air quality consultant needs to work closely with the transport consultant and use consistent traffic data.

Site-specific monitoring is not always required, but it strengthens the assessment significantly. Where baseline concentrations are critical to the assessment — for example, if the site is near an AQMA or close to busy roads — diffusion tube monitoring for a period of at least three months (ideally six to twelve months) provides reliable local data. Where time does not permit monitoring, the consultant can use data from the council's monitoring network or background concentration maps, with appropriate adjustments.

The Institute of Air Quality Management (IAQM) is the professional body for air quality practitioners in the UK. Their published guidance documents — including guidance on land-use planning and development control, construction dust assessment, and air quality assessment methodology — are widely adopted by local authorities as the standard for assessing air quality impacts. Planning authorities and their consultees expect AQAs to follow IAQM methodology, and departures from it will need justification.