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.

In such cases the application should be accompanied by such a report.

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.

Mitigation first approach

In certain cases, for example where the scale of the development is such that it would be prohibitively expensive to undertake an air quality assessment, it is possible to follow a “mitigation first” approach.  This approach requires the applicant to agree with the Council an appropriate scheme of mitigation with respect to air quality.

An example of where such an approach may be agreed is a conversion of a retail unit to residential within an existing air quality management area (or area of concern).

Scope of an air quality impact assessment

Any report should be detailed enough to enable 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 Public Protection and Health Department 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.

Several models are available giving greater or lesser degrees of uncertainty in predictions.  It should be remembered that the Design Manual for Roads and Bridges (DMRB) is a screening tool only, and if predictions show levels of pollutants within 10% of the objective it will be necessary to conduct a more detailed assessment using advanced atmospheric dispersion modelling packages. 

Whichever model is selected the predictions should be verified against local monitoring data. Suitable data can be found on the Review and Assessment 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. It is therefore necessary for air quality impact assessments to show a sensitivity analysis of their results taking into account the scenario where vehicle emissions remain at baseline levels throughout the operation of the development.

If using the the Design Manual for Roads and Bridges (DMRB) your attention is drawn to IAN170/12 (Updated air quality advice on the assessment of future nox and NO2 projections for users of DMRA Volume 11, Section 3,Part 1 ‘Air Quality') which outlines changes to the procedure and a gap analysis methodology to be followed.

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

Study area

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.  This may in some cases be quite a wide study area, dependant on the scale and location of the development.

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

It may be necessary to utilise officers' local knowledge to refine traffic data assumptions based on the area of the study. In addition, it may be required that a road link is broken into multiple links to represent congestion patterns. This will depend on the detail of the assessment.

Traffic Data as outlined above should be presented as part of the scoping report and agreed with this office

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 those in areas where there is the cumulative impact from a number of developments or where a significant air quality impact is likely, you may be required to undertake an emissions assessment and damage costs calculation. Damage Costs are an estimation 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

The Damage Costs for NOX was revised in September 2015 and the latest costs should be used.

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.

Impact of the development

It is recommended developers follow the methodology outlined in Development Control:

  • Planning for Air Quality, (May 2015 v1.1 Update)
  • Environmental Protection UK, in order to describe the impact of the development using a consistent descriptive terminology as recommended by the Institute of Air Quality Management.  

Guidance on this, together with the general content of assessments can be found in the Environmental Protection UK publication Development Control: Planning for Air Quality (May 2015 V1.1 Update).

AQMA special considerations

Where a development is located within an AQMA , or likely to have an impact within an AQMA it is essential that Air Quality is considered as part of the planning process.

It will be necessary to scope a suitable assessment (as above), or to scope "out" Air Quality prior to submitting an application (for example where a proposed development is obviously likely to result in an improvement to local air quality).

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

Following my submission

A judgement will be made based on the outcome of the impact assessment as to the significance of the development on local air quality.  Many factors are considered as part of his process including the size and scale of the development, cumulative impact in an area and the presence of local areas of concern. 

In cases where there is considered to be an overriding, or high priority consideration discussion would be held between the applicant / agent and the Regulatory Services and Health department.  This may include discussions around;

  • Provision of suitable mitigation measures to reduce or remove overriding impacts
  • On site or Off Site mitigation to an appropriate level (perhaps determined by the Damage Costs approach outlined above)
  • Consideration of offsetting the impact, for example financial contributions to our Action Planning work
  • Financial contributions to air quality monitoring work

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
  • 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

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