Air Quality SPD

Ended on the 17th October 2018
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Appendix 2

Air Quality Assessment Protocol to Determine the Impact of Vehicle Emissions from Development Proposals

An air quality assessment should clearly establish the likely change in pollutant concentrations at relevant receptors resulting from the proposed development during both the construction and operational phases. It must take into account the cumulative air quality impacts of committed developments (i.e. those with planning permission).

Air quality assessments should consider NOx and PM emissions and NO2 and PM concentrations

Key Components of an Air Quality Assessment

The assessment will require dispersion modelling utilising agreed monitoring data, traffic data and meteorological data. The modelling should be undertaken using recognised, verified local scale models by technically competent personnel and in accordance with LAQM TG.16. The study will comprise of:

  1. The assessment of the existing air quality in the study area for the baseline year with agreed receptor points and validation of any dispersion model;
  2. The prediction of future air quality without the development in place (future baseline or do-nothing);
  3. The prediction of future emissions and air quality with the development in place (with development or do-something).
  4. The prediction of future emissions and air quality with the development (with development or do-something) and with identified mitigation measures in place.

The assessment report should include the following details:

  1. A detailed description of the proposed development, including:
    • Identify any on-site sources of pollutants;
    • Overview of the expected traffic changes;
    • The sensitivity of the area in terms of objective concentrations;
    • Local receptors likely to be exposed;
    • Pollutants to be considered and those scoped out of the process.
  2. The relevant planning and other policy context for the assessment.
  3. Description of the relevant air quality standards and objectives.
  4. The assessment method details including model, input data and assumptions:
  5. For traffic assessment;

    • Traffic data used for the assessment;
    • Emission data source;
    • Meteorological data source and representation of area;
    • Baseline pollutant concentration including any monitoring undertaken;
    • Background pollutant concentration;
    • Choice of base year;
    • Basis for NOx:NO2 calculations;
    • A modelling sensitivity test for future emissions with and without reductions;

    For point source assessments:

    • Type of plant;
    • Source of emission data and emission assumptions;
    • Stack parameters – height, diameter, emission velocity and exit temperature;
    • Meteorological data source and representation of area;
    • Baseline pollutant concentrations;
    • Background pollutant concentrations;
    • Choice of baseline year;
    • Basis for deriving NO2 from NOx.
  6. Model verification for all traffic modelling following DEFRA guidance LAQM.TG (16):
  7. Identification of sensitive locations:
  8. Description of baseline conditions:
  9. Description of demolition/construction phase impacts:
  10. Summary of the assessment results:
    • Impacts during the demolition/construction phase;
    • Impacts during the operation phase;
    • The estimated emissions change of local air pollutants;
    • Identified breach or worsening of exceedences of objectives (geographical extent)
    • Whether Air Quality Action Plans are compromised;
    • Apparent conflicts with planning policy and how they will be mitigated.
    • Uncertainties, errors and verification
  11. Mitigation measures.

Air Quality Monitoring

In some case it will be appropriate to carry out a short period of air quality monitoring as part of the assessment work. This will help where new exposure is proposed in a location with complex road layout and/or topography, which will be difficult to model or where no data is available to verify the model. Monitoring should be undertaken for a minimum of six months using agreed techniques and locations with any adjustments made following Defra technical guidance LAQM.TG (16).

Assessing Demolition/Construction Impacts

The demolition and construction phases of development proposals can lead to both nuisance dust and elevated fine particulate (PM10 and PM2.5) concentrations. Modelling is not appropriate for this type of assessment, as emission rates vary depending on a combination of the construction activity and meteorological conditions, which cannot be reliably predicted. The assessment should focus on the distance and duration over which there is a risk that impacts may occur. The Institute of Air Quality Management (IAQM)[18] has produced a number of documents to which this guidance refers. The document `Guidance on the Assessment of the Impacts of Construction on Air Quality and the Determination of their Significance' should be the reference for reporting the construction assessment.

Cumulative Impacts

The NPPF (paragraph 124) recognises that a number of individual development proposals within close proximity of each other require planning policies and decisions to consider the cumulative impact of them. Difficulties arise when developments are permitted sequentially, with each individually having only a relatively low polluting potential, but which cumulatively result in a significant worsening of air quality. This will occur where:

  • A single large site is divided up into a series of units, such as an industrial estate or retails park;
  • A major development is broken down into a series of smaller planning applications for administrative ease; and
  • There are cumulative air quality impacts from a series of unrelated developments in the same area.

The first two cases the cumulative impact will be addressed by the likelihood that a single developer will bring forward an outline application for the whole site which should include an air quality assessment as part of an Environmental Assessment. For major developments that are broken down into a series of smaller planning applications, the use of a `Master or Parameter Plan' that includes an air quality assessment will address the cumulative impact.

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