Four things often overlooked during Air Quality Assessments

Temple is a leading planning, environment and sustainability consultancy. Our experienced air quality team undertake numerous reviews of air quality assessments submitted with planning applications, as well as carrying out air quality assessments and monitoring on projects. Our track record brings us unique insights into how air quality assessments are conducted and what can be often overlooked in the process.

1. Not considering all sources of air pollution:

Many air quality assessments will use dispersion modelling to estimate pollutant concentrations in areas where the development can have an impact. If a scheme generates traffic or includes a large boiler, the areas impacted may include the facades of existing residences, schools or hospitals. However, where the scheme is in an area with already poor air quality, such as a city centre, pollutant concentrations at the proposed facades may be estimated to ensure air quality objectives (AQOs) are met.

Car Parks:

Most consultancies consider the effects of road traffic and permanent boilers well; however, some schemes include internal parking, where air from the car park is forced through one or two horizontal vents to the outside. These vents are occasionally located near residential windows or balconies which may lead to a build up of pollutants and a much higher exposure to pollution. In some areas where pollution levels are already high, this could lead to exposure exceeding AQOs. However, internal air quality can be improved if vents are located at a suitable distance from residential windows and designed in a way to disperse pollution outside effectively.

Diesel Generators:

Polluting diesel generators are occasionally installed in residential or commercial schemes to provide power for life-saving equipment during power cuts. Operating a generator for less than 18 hours per annum will result in emissions not breaching AQOs for nitrogen dioxide (NO₂), a key pollutant. This means that if one generator is installed, the effects of testing and servicing a generator for a few hours each year alongside operation during power cuts would likely be acceptable. However, the number of hours over which generators at a site operate could increase if more than one generator, or a generator and large boiler is proposed. Testing multiple generators sequentially rather than simultaneously also increases the chances of air quality being unacceptable. This need not be an issue if the generators are appropriately assessed, and generators are designed to minimise emissions of air pollutants or maximise their dispersion.

2. Not considering odour:

In some instances, air quality assessments for a proposed scheme fail to account for odour issues. For example, one assessment mentioned that the Proposed Development was being built around a waste processing facility, which is known to generate odours due to its decomposing food waste but did not fully assess its impacts. Odour issues at a site can be reduced if a buffer zone around the source of the odours is accounted for in the design.

3. Not modelling air quality appropriately:

The difficulty with using modelling to assess air quality is that the outputs are only as good as the inputs! We have seen various assessments which have used challengeable traffic data (influencing the amount of pollution generated) or inappropriate data on background air pollution which is very important considering it is never possible to model all small sources of air pollution, but which all add up. Some don’t add buildings or the ‘street canyons’ they create (which significantly affects pollutant dispersion) and others haven’t ‘verified’ their model correctly using local monitoring data.

In some instances, these changes could make the difference between an air quality objective being breached at residential facades on-site or complied with. They may also affect the degree of impact predicted at existing receptors and consequently whether the site should consider detailed mitigation in its design or not.

4. Not considering mitigation design in enough detail:

Air quality assessors often describe mitigation proposals at a high level and in some cases, this means they may not be well thought through. Applicants have sometimes recommended ‘green infrastructure’ as a means of dispersing pollutants. However, research indicates that dispersion may sometimes worsen if trees or other vegetation is planted inappropriately; depending on factors like wind direction and local building heights. Blocking pollutant dispersion could lead to pollutants accumulating outside residential facades unintentionally, so where this happens, it would be better not to plant the trees or design them into the building differently. Talking to the landscaping team early in the design can ensure air quality at the site is enhanced, not compromised, by vegetation.

As air quality and odour assessments are important tools in shaping how schemes are designed, it is important the assessment includes all sources of pollution; and provides enough detail on the mitigation design to enable other members of the design team and the planning authority to fully understand how air quality impacts should be mitigated.

Based on our experience, Temple’s Air Quality team are well geared to help with any development schemes you have. Our experience across sectors and projects ensures we are well placed to provide comprehensive assessments. Please get in touch.