Air Quality SPD

Ended on the 17th October 2018
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(4) 5 Development Classification, Assessment and Mitigation

The assessment of air quality for relevant planning applications should follow a three-stage process:

  1. Determining the classification of the development proposal;
  2. Assessing and quantifying the impact on local air quality;
  3. Determining the level of a mitigation required by the proposal to make the scheme acceptable.

Not all development may fit into this classification model and further guidance on specific development has been provided in Section 5.5 of this guidance.

5.1 Stage 1 - Development Type Classification

The classification of developments is shown in tables 1 and 2. The assessment and mitigation of development proposals is shown in figure 1.

Table 1 – Air quality classification of developments

Scheme Type





Below threshold criteria for a Transport Assessment[4] or Travel Plan

Meets threshold criteria for a Transport Assessmentor Travel Plan


Medium type developments which also trigger any of the following criteria:

i) Where development is within or adjacent[5] to an AQMA or CAZ

ii) Where development requires an EIA[6] and air quality is to be considered

iii) Where any of the criteria in Table 2 are triggered


None (other than for exposure)

None (other than for exposure)

Air Quality Assessment required including an evaluation of changes in emissions[7]


Type 1

Types 1 and 2

Types 1,2 and 3

The Department for Transport (DfT) threshold criteria for Transport Assessments (TA) can be found in appendix 1.

Table 2 – Additional Trigger Criteria for Major Developments

  • Proposals in areas where sustained compliance with EU Limit Values may be at risk[8]
  • Any development proposing a net increase of 100 or more parking spaces
  • Any development that could increase the existing traffic flows on roads of > 10,000 AADT by 5% or more
  • Any development that causes a change in LDV (cars and small vans) flows of:

- more than 100 AADT within or adjacent to an AQMA, CAZ or exceedance area

- more than 500 AADT elsewhere

  • Any developments that could increase traffic flows by 5% or more in road canyons[9] (or creates a canyon) with > 5,000 AADT
  • Any development that causes a change in HDV flows (lorries, large vans and buses) of:

- more than 25 AADT within or adjacent to an AQMA, CAZ or exceedance area

- more than 100 AADT elsewhere

  • Proposals that could introduce or significantly alter congestion (DfT Congestion) and includes the introduction of substantial road infrastructure changes
  • Proposals that reduce average speeds by more than 10 km per hour
  • Proposals that include additional HGV movements by more than 10% of total trips
  • The construction, widening or repositioning of a road in the vicinity of sensitive receptors[10]
  • Where significant demolition and construction works are proposed[11]
  • Where a centralised combustion unit of thermal input >300kWh is proposed
  • All biomass boiler and other large novel fuel appliance applications
  • All stand-by/short-term power generation units regulated by the Environment Agency

5.2 Stage 2 - Air Quality Impact Assessment

MINOR and MEDIUM Classified Proposals

Smaller development proposals may not in themselves create an additional air quality problem but will add to local air pollution and potentially introduce more people likely to be exposed to existing levels of poor air quality. An assessment of the likelihood of introducing additional exposure will be determined using the following criteria:

  • The proposal is adjacent to or within an AQMA;
  • The proposal is in a location 20m from roads at or above the relevant national objective highlighted on the DEFRA GIS modelled maps -
  • The proposal is one of the Land Use types:

    - C1 to C3;

    - C4 (Homes of Multiple Occupation);

    - D1

    - and within 20m of roads with >10,000 AADT

The outcome of the exposure assessment will determine the level of mitigation required to make the development acceptable. Should there be no acceptable mitigation the recommendation may be to consider refusing the proposal on air quality grou

Figure 1 – Classification, assessment & mitigation of new developments


MAJOR Classified Proposals

It is important that all major schemes should identify suitable assessment requirements and potential mitigation through pre-application discussions. The scale and nature of this type of proposal is such that a detailed air quality assessment will be required to determine the impact on public health and the local environment. The assessment requires:

- The identification of the level of exposure through the change in pollutant concentrations including cumulative impacts arising from the proposal, during both demolition/construction operations and operational phases. Mitigation measures should be identified and modelled where practicable.

- The calculation of pollutant emissions costs from the development.

  1. The methodology to be used for the determination of pollutant concentration change should meet the requirements of the Department for the Environment, Food and Rural Affairs (DEFRA) Technical Guidance Note LAQM TG. (16)[12] (or any subsequent revisions). Further details of the air quality assessment requirements can be found in Appendix 2 and through the Council's Environmental Health Team.
  2. All Air Quality Assessments received will be assessed by the Council against the requirements of this Technical Guidance Note. If the requirements are not met, Warwick District Council may request that the applicant carries out the assessment again. If the assessment does not meet the required standards, the application may be refused.

  3. The pollutant emissions costs calculation will identify the damage costs associated with the proposal and will assist WDC in assessing the overall impacts on air quality arising from major developments. WDC will use the damage costs in considering the appropriate scale and kind of mitigation that is required to make certain major schemes acceptable in terms of air quality. The overall benefit of the scheme will be taken into account in making the site acceptable. The calculation should utilise the most recent DEFRA Emissions Factor Toolkit[13] to estimate the additional pollutant emissions from a proposed development and the latest DEFRA IGCB Air Quality Damage Costs for the specific pollutant of interest, to calculate the resultant damage cost[14]. The calculation process includes:
    • Identifying the additional trips generated by the proposal (from the Transport Assessment);
    • The emissions calculated for the pollutants of concern (NOx and PM10) [from the Emissions Factor Toolkit];
    • The air quality damage costs calculation for the specific pollutant emissions (from DEFRA IGCB);
    • The result is totalled for a five-year period to enable mitigation implementation.

The calculation is summarised below. Further information can be obtained from the Council's Environmental Health Team. Should there be no net increase in trips arising from a development scheme then the damage costs are zero. Further information on damage costs can be found in appendix 3.

Road Transport Emission Increase =
Σ[Estimated trip increase for 5 years X Emission rate per 10 km per vehicle type X Damage Costs]

(3) 5.3 Stage 3 - Mitigation

Where mitigation is not integrated into a proposal, we will require this through planning conditions. The NPPF (paragraph 152) states that "where adequate mitigation measures are not possible, compensatory measures may be appropriate". If on-site mitigation is not possible then WDC will seek compensation for the identified air quality impacts through a Section 106 Agreement or similar agreement. Each development will require a brief mitigation statement which must include those identified mitigation/ compensation measures to be equivalent to the value of their emissions calculation.

Example mitigation measures are presented for each type of proposal that demonstrate a minimum requirement. This is not an exhaustive list but a suggested suite of measures and will be adapted for particular locations and needs identified by the Council. We welcome the opportunity to work with developers to devise innovative measures that will lead to improving local air quality.

Type 1 mitigation is listed in Table 3 and Types 2 and 3 are listed in Tables 4 and 5 respectively.

Due to elevated concentrations of particulate matter in the district, Medium and Major developments will be required to implement suitable abatement controls for the use of non-road mobile machinery (NRMM) – see Table 6.

Type 1 Mitigation

Table 3 – Type 1 Mitigation

Plug-in Vehicle Re-Charging:


1 charging point per unit (dwelling with dedicated parking) or 1 charging point per 10 spaces (unallocated parking) and ensure appropriate cabling is provided to enable increase in future provision


10% of parking spaces (32 amp) which may be phased with 5% initial provision and the remainder at an agreed trigger level. At least 1 charging unit should be provided for every 10 disabled parking spaces. Where 50 parking spaces or more are provided then 1 rapid charging unit (43kW/50kW) per 50 spaces shall also be considered and parking time limited to a maximum of 1 hour for public access car parks.


10% of parking spaces which may be phased with 5% initial provision and the remainder at an agreed trigger level. At least 1 charging unit should be provided for every 10 disabled parking spaces. Where 50 parking spaces or more are provided then 1 rapid charging unit (43kW/50kW) per 50 spaces shall also be considered and parking time limited to a maximum of 1 hour.

All charging unit shall be installed where practical. Developers installing public charging points shall ensure that the National Charge point Registry is updated.

Code of Construction Practice

Construction Environmental Management Plan (CEMP) to be incorporated into MEDIUM and MAJOR developments and agreed with Council Officers. This shall include

NRMM controls (see table 6)

Green Infrastructure and planting

Where it can be shown that such infrastructure will reduce exposure from air pollution

Type 2 Mitigation

The following tables provide a suite of measures to be considered where appropriate.

Table 4 – Type 2 Mitigation

  • Monitored Travel Plan, including mechanisms for discouraging high emission vehicle use and encouraging the uptake of low emission fuels and technologies[15]
  • Measures to support public transport infrastructure and promote use
  • Measures to support cycling and walking infrastructure
  • Measures to support an Electric Vehicle Plan
  • Designated parking spaces and differentiated parking charges for low emission vehicles
  • Non-road mobile machinery (NRMM) controls (see Table 6)

Commercial development specific:

  • Use reasonable endeavors to use/require vehicle use complying with the latest European Emission Standard from premises opening and to be progressively maintained for the lifetime of the development.
  • Provide a fleet emission reduction strategy/low emission strategy, including the uptake of low emission fuels and technologies, such as ultra-low emission service vehicles

Type 3 Mitigation

Table 5 – Type 3 Mitigation

Off-set mitigation to support:

  • Implementation and operation of Clean Air Zones (CAZ), Low Emission Zones (LEZ) or Low Emission Strategies (LES)
  • Growth in low and ultra-low emission public transport, including buses
  • Electric Vehicle Plans
  • On-street EV recharging
  • Air Quality Monitoring programs
  • Car clubs (including electric) and car sharing schemes
  • Cycling Hubs and corridors, including bike and e-bike hire schemes
  • Plugged-in development and demonstration schemes e.g. new occupants given trial demonstration of plug-in vehicle
  • Contributions to subsidised public transport for staff or residents
  • Low emission waste collection services
  • Contributions to renewable fuel and energy generation projects
  • Infrastructure for low emission, alternative fuels e.g. refuse collection and community transport services

Further information on the suitability of mitigation for developments can be obtained from the Council's Environmental Health Team and through pre-application discussions.

Table 6 – Non-Road Mobile Machinery (NRMM) Controls

NRMM of net power between 37kW and 560kW will be required to meet the standards based upon the engine emissions standards in EU Directive 97/68/EC and its subsequent amendments. This will apply to both variable and constant speed engines for both NOx and PM. These standards are:

  1. NRMM used on the site of any MEDIUM classified development will be required to meet Stage IIIA of the Directive as a minimum.
  2. NRMM used on any MAJOR classified development will be required to meet Stage IIIB of the Directive as a minimum.

From 1 September 2020 the following changes will apply:

  • (a) NRMM used on any construction or demolition site within urban areas will be required to meet Stage IIIB of the Directive as a minimum.
  • (b) NRMM used on any MEDIUM or MAJOR classified development will be required to meet Stage IV of the Directive as a minimum.

The requirements may be met using the following techniques;

(a) Reorganisation of NRMM fleet (b) Replacing equipment (with new or second-hand equipment which meets the policy) (c) Retrofit abatement technologies (d) Re-engining.

All eligible NRMM should meet the standards above unless it can be demonstrated that the machinery is not available or that a comprehensive retrofit to meet both PM and NOx emission standards is not feasible.

(1) 5.4 Assessing the acceptability of a scheme

WDC will determine the acceptability of a scheme and its location based on the outcome of the air quality assessment and the provision of on-site and/or off-set mitigation.

While applicants may present evidence as to the significance of scheme impacts or the impact of air quality on a scheme, WDC reserves the right to determine the acceptability of a scheme based on local air quality knowledge and the cumulative impacts of schemes.

5.5 Specific Issues

5.51 Heating

Minimum emission standards that are outlined below should be applied where relevant.

Heating plant on developments outside of AQMA or urban areas that are >500m from an AQMA:

Individual gas fired boiler <40mgNOx/kWh

Spark ignition engine 250mgNOx/Nm3

Compression ignition engine 400mgNOx/Nm3

Gas turbine 50mgNOx/Nm3

Heating plant on developments in or adjacent to AQMA (within 500m of an AQMA):

Individual gas fired boiler <40mgNOx/kWh

Spark ignition engine 95mgNOx/Nm3

Compression ignition engine 400mgNOx/Nm3

Gas turbine 20mgNOx/Nm3

5.52 Biomass boilers and other large novel fuel appliances

Biomass boiler provision has increased over recent years, supported by the financial benefits of the Government's Renewal Heat Incentive (RHI)[16]. However, the emissions from biomass plant can lead to significant emissions of NOx and PM, even from relatively small plant.

Biomass boiler plant and other large novel fuel appliance applications will be subject to a full air quality assessment and will be resisted in our urban areas unless mitigation is provided to achieve emissions of NOx and PM that are equivalent or lower than gas fired plant (see 5.51)

5.53 Standby / back-up power generation

All standby/back-up power generation applications will require a full air quality assessment to assess the acceptability of the site for such a scheme.

WDC expect all such assessments to include reasoning as to whether gas powered generation can be utilised in the first instance eg identify the provision of suitable gas mains in the vicinity.

Any diesel-powered generators will be required to incorporate abatement equipment such as selective catalytic reduction and particulate trap (SCRT).

5.54 Permitting under the Pollution Prevention and Control Act 1999 and the Environmental Permitting (England and Wales) Regulations 2016 (as amended)

Industrial processes which may range from large industrial plant to dry cleaners and paint spraying workshops, are regulated by the Environment Agency (Part A1 processes) and the Council (Part A2 and Part B processes). The planning regime must assume that the permitting regime will ensure the processes comply with their permits and the Act. The planning regime can, however consider whether a land use is appropriate and it must consider the exposure to pollutants.

All Part A and B Process developments requiring planning applications and where NOx and PM emissions are relevant will be required to carry out a detailed air quality assessment

5.55 Mechanical Ventilation

Air quality concentrations may affect the suitability of certain locations for sensitive developments and this should be assessed in line with section 5.2.

Some applications in areas of poor air quality have proposed mechanical ventilation as a solution to overcoming potential exposure to poor air quality. This may involve sealed windows / triple glazing with trickle vents and a forced ventilation system, incorporating filters to remove pollutants.

Not only do such schemes increase the energy requirements of developments but also provide a questionable living space in what is essentially a 'hermetically sealed unit' and should not be seen as an acceptable solution to mitigating against exposure, particularly where mechanical failure would make the situation even worse.

Any sensitive development in an area of pollutant exceedance should incorporate the following considerations:

- The sensitive development should be at least 20m from the curb, with the arrangement of living space to afford further separation from a pollutant source

- Take account of the height separation of living accommodation from a road source eg can residential dwellings be provided from floors 2 / 3 upwards with commercial premises at lower levels

- The use of green infrastructure to provide a barrier to an adjacent pollution source (see 5.56)

- The projected length of time that the sensitive dwelling will be exposed to elevated pollution levels from scheme completion

- Reduce the potential for internal pollution eg through electric cooking provision

- Provision of monitoring data to support applications for sensitive developments. This requirement should be agreed with the Council's Environmental Health Team prior to commencement of monitoring

Where the above considerations cannot achieve acceptable exposure for a sensitive development then consideration should be given to the refusal of the scheme.

5.56 Green Infrastructure and Planting

Plants and trees may provide an aesthetically pleasing aspect to a scheme and may also be used to provide a barrier from a pollutant source such as a trafficked road.

While there is conflicting evidence as to whether green infrastructure can help reduce concentrations of NO2, it is acknowledged that certain types of shrubs and trees are effective at removing particulates from the atmosphere.

For example, a living wall or a framework for climbing plants may offer some protection between a pollution source such as a road and a dwelling. Additionally, certain types of trees such as varieties of pine, planted between a road an residential accommodation may help reduce exposure to particulates.

Careful consideration is needed as to the type of green infrastructure to be used as certain tree species can produce their own emissions, such as isoprenes, which may exacerbate air pollution.

5.57 Section 106 Agreements and the Community Infrastructure Levy (CIL)

WDC has adopted the Community Infrastructure Levy (CIL), however, our list does not include infrastructure to improve air quality, therefore, subject to the rules on pooling, we will seek Section 106 Agreements (Town and Country Planning Act 1990) and other relevant obligations with developers to secure mitigation, including off-set, on larger schemes (Medium and Major) where appropriate.

Section 106 Agreements will only be sought where the following legal tests are satisfied:

- necessary to make the development acceptable in planning terms

- directly related to the development; and

- fairly and reasonably related in scale and kind to the development.

Additionally, Section 106 Agreements must also satisfy the policy tests in the NPPF, paragraph 203.

[5] Where development has potential to impact on concentrations in AQMA or CAZ


[7] Assessment includes monetisation of the impacts arising from emission changes in line with Defra IGCB Damage Costs

[8] Where current monitoring data shows NO2 annual average concentrations of 36 ug/m or more

[9] Where the height of buildings adjacent to both sides of the road are higher than the width between them. Local knowledge and professional judgement will be required to help identify road canyons

[10] See section 5.2

[11] Significance determined by professional judgement based on scale of works and proximity of sensitive receptors

[15] Where the developer funds the monitoring of a travel plan

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