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Air Quality Assessment

Poor Air Quality can impact people's health. An Air Quality Assessment seeks to establish whether a proposed development is suitable in a given area. Is the air quality good enough for people to live there? Will it make the air quality in the area worse?

A relatively new concept in Air Quality Assessment is Air Quality Neutrality. In presenting a proposal for a new development is required to prove that it will not worsen air quality. A car free development, running on electric heating in a central urban location, may easily meet these criteria. However, for sub-urban developments things can be more difficult.

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Air Quality Baseline Study

Ammonia Emissions Assessment

Indoor Air Quality Assessment

Detailed Air Quality Assessment

Air Quality Assessment Screening Thresholds

Simple Air Quality Assessment

Air Quality in London

Downwash Analysis


Air Quality Impact Assessment Explained

There are obvious developments that are associated with air quality impacts these might include coal fired power plants, oil refineries, waste incinerators (EfW).

There is often air quality impacts associated with the construction phase of most projects, traffic dust and smoke from poorly maintained plant can be a problem.

There are direct and indirect emissions to be considered, a factory that make plastic milk bottles for example might have direct emissions (impacts) from the heating of plastics etc, and indirect emissions from the power station where is sources the energy to heat the plastics.Steam is a visually polluting emission that many find of concern, when in most cases steam contains little more than water vapour.

An air quality impact assessment may contain:

- Baseline Studies

- Impact Prediction

- Mitigation

- Monitoring

NOx emissions are also carefully considered within larger urban areas. The introduction of large number of condensing boilers (which a produce higher levels of NOx) within new build schemes are typically frowned upon. Combined heat and power is a good alternative, although plant will need to carefully specified to ensure minimised NOx emissions.

Indoor Air Quality Assessment

Most people in Europe spend 90% of their time indoors so indoor air quality is very important. Indoor Air quality has a major influence on health and comfort of building occupants. Indoor air quality can be lowered via the presence of a great many gaseous and particulate elements which lower air quality and have harmful effects on occupants.

air_quality_assessmentThere are a great many sources to be considered when assessing air quality indoors.  In fact just about everything that an occupant does in abuilding including breathing has the potential to lower the air quality if the air volume is not sufficiently ventilated.

Offices and Homes alike use a large variety of cleaning products, cosmetic products and many home have boilers or log burners which have the potential to introduce combustion by products in to the indoor air volume.

When SWEL undertake indoor air quality monitoring we typically monitor for around 40 "determinants", that is to say different chemicals that may point out significant sources of pollutants. We can then match these determinants (Para-dichlorobenzene for example) to a common house hold source (Moth Balls). Although this compound is also used in in disinfectants and deodorants!

Quite often the identification of an unpleasant odour by the buildings occupants is the trigger for a indoor air quality assessment being undertaken, and in these instances it is important to characterise the odour and start looking in the right direction. Hidden mold can often cause odours, and this is fairly easy to find without undertaking any monitoring.

However with other odours such as solvents it is extremely useful to undertake air quality monitoring so as to narrow down a potentially long list of sources.

Although VOCs in paints and other surface coatings are being phased out they represent some of the most polluting substances that are used in the home and work place. A classic example of this is painting a nursery prior to the birth of child. Gloss paints, and spirit based varnishes are significant.

Further Detail on Indoor Air Quality Monitoring

Samples can be collected using a TD tube packed with sorbent, in which one end of the tube is fitted with an open mesh diffusion cap for VOC collection.  The tubes are sent with brass caps; when sampling is required the cap is removed from the sample end (the side of the tube marked with a groove) and replaced with the diffusion cap.  The diffusion/gauze cap is used to provide a regulating barrier to diffusion.  Passive sorbent tubes can be deployed for two weeks or less depending on the specific project and limit of detection requirements.  The diffusion sampler is replaced with the original brass cap when sampling is complete.  Each tube has a unique reference to allow simple identification of the sample.  The laboratory reports time weighted average concentrations in µg/m3 for those VOCs with published uptake rates.  For those without, the laboratory reports contaminants as ng/tube.

I’ve asked my colleagues to provide costs for our UST – it will include the key indicator compounds for petroleum hydrocarbons – BTEX, Nap, TPH C6-12 etc.

CO2: An Indirect Measure of Indoor Air Qaulity

ASHRAE (American Society of Heating, Refrigeration and Air Conditioning  Engineers) standards historically use CO2 levels as a marker for indoor air  quality. Levels of CO2 in excess of 700 ppm over outdoor levels (typically 350  ppm), or usually over 1,000 ppm total, are an indication of “poor” indoor air  quality. Such levels of CO2 can indicate that air is not being refreshed enough  so that CO2 is built up from the exhaled breath of the building occupants. At  the levels typically found in IAQ investigations, CO2 is not a toxicity concern  (OHSA PEL = 5,000 ppm), only a gross indicator of possible contamination  from one of the five sources listed above. If the building is ventilated enough  to reduce CO2 levels, it often solves the IAQ problem by dilution. PIDs  complement CO2 monitors by providing a direct measurement of VOCs and  help locate their sources

Air Quality and Planning

The IAQM Guide for Planning Applications gives details of two "levels" of Air Quality Impact Assessment:

Simple Air Quality Impact Assessment

This would involve the detailing of Good Design as below, and a qualitative assessment of Air Quality Impacts. If the development were small for example and the Baseline Air Quality was good, then the impact could well be low.

Detailed Air Quality Impact Assessment

As well as the detailing of Good Design this would include a quantitative assessment. A quantitate assessment would likely involve extensive data collection and then modeling of the site using Aermod or similar modeling program (we use Aermod). In this way a quantitative assessment is made.

Air Quality Impact and Good Design

There a number of suggestion for design and specification that are included with the IAQM Guide:

Street Canyon

No “Street Canyon” it created. There are large gaps between buildings. This will allow air to circulate and disperse street level air pollution.

Delivery of Sustainable Development

“Delivering sustainable development should be the key theme of any application”. This is a wide ranging statement, there are various sustainable features incorporated in the developments design.

Minimisation of Public Exposure

There are no habitable rooms. Any vents of chimney stacks will be sited towards the central access road so as to maximise distances of point source emissions from dwelling. Chimneys may be installed pending relevant permissions but are not sought as part of this planning application. Vents would serve for building ventilation (HVAC); these will be directed towards the site interior, for above stated reasons.

Charging Points Provision of Electrical Vehicle

Charging points to the ratio of 1 for 1000m2 is required. The floor area of each unit is 225m2. e.g. The development of 20 units. Total floor area is 4500m2. 4 charging points are required. 

Travel Plans

Owing the general planning use type it is not thought practical to prepare a Green Travel Plan. For example TRICS data or similar would not be detailed enough to form targets, and as such any such report would be largely subjective in nature, as no clear targets could be defined. 


All gas-fired boilers to meet a minimum standard of <40 mgNOx /kWh.

Air Quality in London

London does receive a lot of attention with regards to Poor Air Quality, however there are many other places in the UK that suffer from poor Air Quality.

There is ample evidence of the adverse health effects caused by air pollution (WHO, 2006). In response to these health impacts, the Air Quality Strategy (AQS) for England, Scotland, Wales and Northern Ireland (Defra, 2008) sets out the UK’s way forward on air quality issues, details objectives to be achieved, and proposes measures to help reach them. These UK objectives largely reflect EU Limit Values (EC, 2008). The GLA and the London boroughs and district councils outside the capital have responsibilities for the management of air quality and must work towards the attainment of AQS objectives.

This study has found that in 2013 there was still significant exposure of the London population to levels of NO2 above the EU limit value and that this exposure is predicted to decline significantly (96%) by 2020. However, current modeling results show that in 2020 there will still be more than 72,000 people living in locations with average NO2 above the EU limit value.

Air Quality Assessment Screening Thresholds

Here are some thresholds that would indicate as to whether you development requires an Air Quality Assessment. These thresholds are used to describe "Major Developments", which would then trigger the requirement for an Air Quality Assessment, some other thresholds are sometimes used, stemming from industry specific guidance.

Air Quality Neutrality Assessment

As of November 2021 The London Mayor's Office Released guidance on Air Quality Neutrality Assessment, this a quite a simple matter for minor developments but for major developments it involves quite a lot of work. 

Recent Air Quality Projects (From Weblog)

Air Quality Impact Assessment Horsham, West Sussex
The Housing Association were concerned that dust and gaseous emissions from the proposed demolition and construction activities would impact on their residents health.
Air Quality Assessment - Norfolk
The assessment of risks in this instance relied on secondary data collected, and used as a baseline. With impacts considered throughout the construction and operational phases of the development.
Air Quality Assessment - Brent, London (NW6)
A resident approached Southwest Environmental Limited with concerns over the quality of air within their living space. It was thought that air quality might be lowered owing to the neighboring property uses.