Air quality and planning 

New development has the potential to affect air quality. Air quality is one of the material planning considerations taken into account as part of the planning decision making process. Air Quality Impact Assessments may be required before an application can be determined.

Air quality assessments

The following list is a non-exhaustive indication of when an Air Quality Impact Assessment may be required. If you are unsure whether an assessment is required please contact us.  It is recommended you check with the Air Quality team before you submit the application as this can save time, and in some cases money.

• any development within an AQMA , or within 500m of existing Air Quality Management Areas
• food retail development >0.2HA (1000m² gross floor space)
• office development >0.8Ha (2500m² gross floor space)
• housing development >1.0 Ha or >80 units
• development likely to lead to an increase of >60 vehicle movements per hour
• development likely to result in increased traffic, congestion, or changes to vehicle speeds (new junctions, roundabouts etc)
• development likely to significantly change the traffic composition
• development significantly increasing car parking provision (>300 spaces or 25% increase)
• development in close proximity (<100m) to busy roads / junctions
• development likely to result in a significant change in air quality, or development of residential properties in an area of already poor air quality.
• poultry establishments > 400,000 birds (mechanical ventilation) or 200,000 (natural ventilation) or > 100,00 (Turkeys) and with relevant exposure within 100m of the unit.
• biomass / CHP / Industrial Installation (see guidance under the biomass and clean air act pages)

This list is NOT exhaustive. An assessment may be required where the cumulative impact of a number of developments in an area are likely to have a negative effect on air quality, regardless of the scale of each individual development.

Scope of an air quality impact assessment

Reports should be detailed enough for the planning authority to determine, with a reasonable degree of certainty, the significance of any air quality impacts and thereby the priority to be given to air quality concerns when deciding an application. The scope of an air quality assessment will depend on the nature of the proposed development and the likely impact.

It is recommended that the scope and methodology of any assessment are agreed with the Air Quality team prior to completion. 

If a development is in close proximity to, or within an existing Air Quality Management Area, the report MUST show there is no adverse impact on Air Quality within the AQMA.  If an adverse impact is predicted suitable mitigation should be suggested which is aimed at reducing this impact as far as is reasonably practicable.

Model type

Modelling should be carried out using a recognised, local scale dispersion model to be agreed with the Local Authority before work commences.

Whichever model is selected the predictions should be verified against local monitoring data. Suitable data can be found on the Monitoring Data pages, or by contacting the Air Quality team.

Sensitivity/gap analysis

Emissions of nitrogen dioxide from vehicles has been predicted to decline over time, purely as a result of advances in vehicle technology. However, recent evidence has shown the predicted decline in concentrations has not occurred. Air quality impact assessments must therefore show a sensitivity analysis that takes into account the scenario where vehicle emissions stay at baseline levels throughout the operation of the development.

The methodology proposed should be agreed with this office and justification presented on the choice, including details of proposed model verification.

Study area

This should be sufficient to encompass the development itself, and any sensitive receptors likely to be affected by the impact of the development as outlined above.  

When agreeing the scope of the report with this office, a map should be included outlining the proposed study area.

Traffic data

The traffic data for each road link should be agreed with this office including;

• source of data
• AADT vehicle flows
• fleet composition
• speed
• if necessary flow patterns

Assessment content

The Impact Assessment should consider:

• to assess the existing air quality in the study area (baseline)
• to predict the future air quality without the development (future baseline) *
• to predict the future air quality with the development without mitigation (with development)
• to predict the future air quality with the development and with any mitigation proposed (with development and mitigation)
• to assess the impact of the construction / demolition phase 
• to consider the cumulative impact of permitted developments within the area

The baseline year should be consistent across all data sources (traffic, met data, monitoring data etc). The study years should be sufficient to compare the following situations:

Low emissions approach

For developments in the categories above, particularly where there is a cumulative impact from multiple developments or where significant air quality impact is likely, you may need to do an emissions assessment and damage costs calculation. Damage costs are an estimate of the economic impact caused by the increased emissions of  NO2 and particulates from the new development.

The exact methodology of an emissions assessment and damage costs calculation should be scoped with the service prior to being undertaken. However in general the following guidance can be used.

Guidance on calculating damage costs

• DEFRA Air Quality Damage Costs Guidance

Damage Costs for NOX and PM should be calculated for the development over 5 years using the Central Estimate in accordance with the guidance, and reported within the assessment. It is acceptable to take account of any mitigation proposed within the emissions assessment and subsequent damage costs calculations providing suitable evidence can be provided.

The final damage costs can then be used to determine a proportionate contribution, or provision of, additional mitigation on site. Where on site mitigation is not possible off site measures may need to be considered.

Meteorological data

The scoping report should state the source and year of the met data giving justification for the choice. Ideally met data should be as local as possible to the site. In many cases Manchester Airport or Rostherne Data is used. Depending on the data used, it may be necessary to carry out a sensitivity analysis of this data.

Sensitive receptors

It is vital that the model consider relevant receptors representative of worst case likely exposure in each of the modelled scenarios.  This may include residential properties, schools or other sensitive uses. Sufficient receptors need to be chosen to be representative of the wider impact of the development.  It may be necessary to include receptors within the proposed development.

In addition, if the development is within an AQMA (or within 500m of an AQMA ) some receptor locations MUST be located within the AQMA at worst case locations.  The location, grid reference and address of each proposed receptor should be agreed as part of the scoping report.

Receptor locations should be presented on a map and agreed with this office

Where the Transport Assessment indicates there will be an adverse traffic impact (including at sites remote from the development), the assessment should include any receptors located nearby to these areas roads and junctions.

Cumulative impact

The cumulative Impact of a number of developments in an area can lead to a gradual deterioration of air quality.  Any assessment must therefore take into account the cumulative impact of all significant live applications in an area, and where necessary propose suitable mitigation to offset the impact.  In addition all phases of the proposed development should be considered together.

The study of the cumulative impact of additional development must be agreed as part of the scoping report

Mitigation

Where an assessment indicates a development is likely to have a significant impact on local air quality, the Council will seek to secure mitigation to offset the impact of the development.  The nature and scale of mitigation required will depend on the nature of the development and also the significance of the air quality impacts.

Examples of mitigation measures which might be considered include (but are not limited to);

• redesign to eliminate / reduce exposure
• traffic reduction / management measures
• restrictions to car parking
• incentivisation of low emission vehicles, such as providing charging services for electric vehicles in line with Building Regulations Approved Document S - Infrastructure for the charging of electric vehicles 
  
• robust travel plans aimed at encouraging modal shift to low carbon transport modes.
• financial contributions (s.106 agreements) to Air Quality Action Planning or Low Emission Strategy Implementation

Contact us

Page last reviewed: 11 September 2023