Air Quality and Planning Applications

Is an air quality assessment required for all developments?

Advice regarding when an air quality assessment should be completed in support of a planning application is provided in the EPUK & IAQM guidance Land-Use Planning & Development Control: Planning for Air Quality.  Table 6.2 of the guidance provides indicative criteria for determining when an air quality assessment is required, this table is reproduced below for ease of reference.  It is recommended that the guidance document is referred to in case of updates.

Table 6.2: Indicative criteria for requiring an air quality assessment

Guidance from Environmental Protection UK and the Institute of Air Quality Management for the consideration of air quality within the land-use planning and development control processes.
January 2017
Institute of Air Quality Management https://iaqm.co.uk/

The development will: Indicative Criteria to Proceed to an Air Quality Assessment*
 1. Cause a significant change in Light Duty Vehicle (LDV) traffic flows on local roads with relevant receptors. (LDV = cars and small vans 3.5t gross vehicle weight).  A change of HDV flows of:
- more than 25 AADT within or adjacent to an AQMA
- more than 100 AADT elsewhere.
 2. Cause a significant change in Heavy Duty Vehicle (HDV) flows on local roads with relevant receptors. (HDV = goods vehicles + buses >3.5t gross vehicle weight).  A change of HDV flows of:
- more than 25 AADT within or adjacent to an AQMA
- more than 100 AADT elsewhere.
 3. Realign roads, i.e. changing the proximity of receptors to traffic lanes.  Where the change is 5m or more and the road is within an AQMA.
 4. Introduce a new junction or remove an existing junction near to relevant receptors.  Applies to junctions that cause traffic to significantly change vehicle accelerate/decelerate, e.g. traffic lights, or roundabouts.
 5. Introduce or change a bus station.  Where bus flows will change by: - more than 25 AADT within or adjacent to an AQMA - more than 100 AADT elsewhere.
 6. Have an underground car park with extraction system. The ventilation extract for the car park will be within 20 m of a relevant receptor.  Coupled with the car park having more than 100 movements per day (total in and out).
 

7. Have one or more substantial combustion processes, where there is a risk of impacts at relevant receptors.

NB. this includes combustion plant associated with standby emergency generators (typically associated with centralised energy centres) and shipping.

 

Typically, any combustion plant where the single or combined NOx emission rate is less than 5 mg/seca is unlikely to give rise to impacts, provided that the emissions are released from a vent or stack in a location and at a height that provides adequate dispersion.

In situations where the emissions are released close to buildings with relevant receptors, or where the dispersion of the plume may be adversely affected by the size and/or height of adjacent buildings (including situations where the stack height is lower than the receptor) then consideration will need to be given to potential impacts at much lower emission rates.

Conversely, where existing nitrogen dioxide concentrations are low, and where the dispersion conditions are favourable, a much higher emission rate may be acceptable.

  *As a guide, the 5 mg/s criterion equates to a 450 kW ultra low NOx gas boiler or a 30kW CHP unit operating at <95mg/Nm3. Users of this guidance should quantify the NOx mass emission rate from the proposed plant, based on manufacturers’ specifications and operational conditions.

Which dispersion model should be used?
An appropriate approved dispersion model should be used. Recommended models include:
For modelling emissions from road traffic:

  • ADMS Roads / Urban / Extra
  • Breeze Roads

For modelling emissions from industrial sources / CHP or similar:

  • ADMS
  • AERMOD

Which meteorological data is appropriate?
An appropriate met office approved meteorological station should be selected, the selection will depend on the location of the site. Suggested meteorological stations include:

  • Rothamsted;
  • Andrewsfield;
  • Stansted;
  • Southend;
  • Shoeburyness Landwick;
  • London City.

For assessment of road traffic one year of meteorological data should be used. Wherever possible the latest available year should be used, but the year should be the same year as the monitoring data and traffic data used in the verification of the model. For industrial sources 3 to 5 years meteorological data should be used.


What are the existing concentrations in the vicinity of the site?
Monitoring data for the local area should be used wherever possible to establish the background concentrations. Monitoring data is available on the Essex Air website (www.essexair.org.uk/). Mapped background concentrations across the UK are available on the Defra website (link to website in guidance section), this may be more appropriate depending on the location of the site relative to the existing monitoring.

What the modelling should include?
Concentrations should be predicted at sensitive receptor locations in a future year (usually the opening year of the development) with and without the development.
A baseline / verification year should also be modelled for comparison against the local monitoring in order to verify the model.
Predicted concentrations are compared against the national standards which are the Air Quality Strategy objective levels (link to objectives in general overview section).

How should the significance of an impact on local air quality be determined?
Criteria to determine the significance of the impact of a development on local air quality are provided in the EPUK & IAQM guidance Land-Use Planning & Development Control: Planning for Air Quality (link to document in guidance section).

Table 6.3 of the guidance provides indicative significance criteria; this table is reproduced below for ease of reference. It is recommended that the guidance document is referred to in case of updates. The text associated with the table should also be referred to.

Table 6.3: Impact descriptors for individual receptors

Land-Use Planning & Development Control: Planning For Air Quality

Guidance from Environmental Protection UK and the Institute of Air Quality Management for the consideration of air quality within the land-use planning and development control processes. January 2017

https://iaqm.co.uk/

Long term average Concentration at receptor in assessment year % Change in concentration relative to Air Quality Assessment Level (AQAL)
1 2-5 6-10 +10
75% or less of AQAL Negligible Negligible Slight Moderate
76-94% of AQAL Negligible Slight Moderate Moderate
95-102% of AQAL Slight Moderate Moderate Substantial
103-109% of AQAL Moderate Moderate Substantial Substantial
110% or more of AQAL Moderate Substantial Substantial Substantial
Explanation
1. AQAL = Air Quality Assessment Level, which may be an air quality objective, EU limit or target value, or an Environment Agency ‘Environmental Assessment Level (EAL)’.
2. The Table is intended to be used by rounding the change in percentage pollutant concentration to whole numbers, which then makes it clearer which cell the impact falls within. The user is encouraged to treat the numbers with recognition of their likely accuracy and not assume a false level of precision. Changes of 0%, i.e. less than 0.5%, will be described as Negligible.
3. The Table is only designed to be used with annual mean concentrations.
4. Descriptors for individual receptors only; the overall significance is determined using professional judgement (see Chapter 7). For example, a ‘moderate’ adverse impact at one receptor may not mean that the overall impact has a significant effect. Other factors need to be considered.
5. When defining the concentration as a percentage of the AQAL, use the ‘without scheme’ concentration where there is a decrease in pollutant concentration and the ‘with scheme;’ concentration for an increase. 6. The total concentration categories reflect the degree of potential harm by reference to the AQAL value. At exposure less than 75% of this value, i.e. well below, the degree of harm is likely to be small. As the exposure approaches and exceeds the AQAL, the degree of harm increases. This change naturally becomes more important when the result is an exposure that is approximately equal to, or greater than the AQAL.
7. It is unwise to ascribe too much accuracy to incremental changes or background concentrations, and this is especially important when total concentrations are close to the AQAL. For a given year in the future, it is impossible to define the new total concentration without recognising the inherent uncertainty, which is why there is a category that has a range around the AQAL, rather than being exactly equal to it.

Page updated: 12/01/2021


Make the most of the Essex Design Guide, register today

As well as ensuring you are always in the know about future changes and updates to the Essex Design Guide, registering with us will enable to you to add and manage bookmarks throughout the site, so your most-used areas of the guide are always easy to find.

Register for updates

© 2021 Copyright Essex County Council. All rights reserved.