Air quality neutral and air quality positive in London
Air quality neutral is a benchmark calculation for building and transport emissions. Air quality positive is a design argument about layout, uses and movement. London schemes often need both.
Every development proposal in London has to be at least air quality neutral, and larger schemes in sensitive locations have to go further and be air quality positive. Those are two different tests with two different outputs. Neutral is a numerical comparison against published benchmarks for building and transport emissions. Positive is a design argument about layout, massing, uses and movement, presented as a statement rather than a calculation.
Treating the second as a longer version of the first is the mistake that produces a Greater London Authority holding objection.
What air quality neutral asks for
Policy SI 1 of the London Plan 2021 sets the requirement. A development should not worsen existing poor air quality, should not create new areas exceeding air quality limits, and should be at least air quality neutral.
Neutral does not mean zero emissions. It means the development's emissions of nitrogen oxides and particulate matter do not exceed the benchmark emissions for a development of that type, size and location. The benchmarks are published by the Greater London Authority in its air quality guidance, and they are revised, so take the current version rather than the one in a report from two years ago.
If the scheme is below both benchmarks, it is neutral. If it is above either, you either redesign, mitigate, or make the case for offsetting with the borough.
The two benchmarks
Building emissions come from combustion on site: gas boilers, any combined heat and power plant, and standby generators. The building emissions benchmark is derived from floor area by land use. A scheme that is fully electric, with heat pumps and no gas, produces building emissions at or near zero and passes this limb without argument.
Transport emissions come from the vehicle movements the development generates. The transport emissions benchmark varies by location, because a site in central London with high public transport accessibility is expected to generate far less vehicle emission per unit than one in outer London. The calculation uses trip generation, trip length and fleet emission factors.
| Limb | Source of emissions | What moves the number |
|---|---|---|
| Building emissions benchmark | Boilers, CHP, generators | Fuel choice, plant efficiency, NOx emission standard |
| Transport emissions benchmark | Vehicle trips generated | Car parking provision, public transport accessibility, trip length |
The design lever on the first limb is fuel. On the second it is parking. A scheme that electrifies heat and reduces car parking usually passes both without any further mitigation, which is why the Energy Statement and the air quality work should be done by people who are talking to each other.
Where air quality positive applies
Air quality positive goes beyond not making things worse. It applies to larger-scale development, including masterplans and schemes in Air Quality Focus Areas, and it asks what the proposal does to improve exposure and air quality for the people who will use it and for those nearby.
The submission is an air quality positive statement, prepared early, because its content is about decisions that are made at masterplan stage and cannot be retrofitted. It should cover:
- the location of sensitive uses, such as schools, nurseries, play space and homes for older people, away from the most polluted frontages
- building massing and street form that allows dispersion rather than trapping pollutants in deep canyons
- the position of ventilation intakes and exhausts relative to sources
- green infrastructure used where it helps and not claimed where it does not
- the movement strategy, including car-free or car-capped development, cycle parking and servicing consolidation
- a commitment to no combustion plant
Massing and street form are the parts most often added late and least convincing when they are. These are the same decisions that drive the design-led approach to site capacity, which we look at in optimising site capacity.
Evidence and method
The calculation sits inside the Air Quality Assessment, alongside the conventional elements: baseline concentrations from monitoring and background maps, dispersion modelling of the operational and construction phases, exposure at proposed receptors, and construction dust risk assessed on the recognised industry method.
Three practical points on the neutral assessment itself. Use the published benchmark version current at submission and say which one. Show the input assumptions, particularly trip rates and their source, because the borough will check them against the transport chapter. And reconcile the building emissions inputs with the energy strategy, since a mismatch between the two documents on whether there is a gas boiler is noticed immediately.
For transport inputs, keep the air quality assessment and the Travel Plan consistent on mode share and parking.
Mitigation that moves a scheme into compliance
In rough order of effectiveness:
- Remove combustion. All-electric heating with heat pumps removes the building emissions limb almost entirely.
- Cut car parking and secure it by condition or obligation, which cuts the transport limb directly.
- Where any gas plant remains, specify it to the emission standard set out in the current GLA guidance and state the figure in milligrams per kilowatt hour.
- Relocate sensitive uses and ventilation intakes within the scheme, which does not change emissions but changes exposure.
- Fund off-site measures through the borough where a residual shortfall remains, which is the last resort rather than the plan.
Green infrastructure is worth including for many reasons and it is a weak air quality mitigation on its own. Claiming a quantified pollutant removal from a green wall will attract a challenge unless the method is published and the figures are defensible.
Focus areas and management areas
Two designations change the weight of the argument. Air Quality Management Areas are declared by boroughs under the local air quality management regime where objectives are exceeded. Air Quality Focus Areas are identified by the Greater London Authority as locations with both exceedance and high human exposure.
A site inside either one attracts closer scrutiny, and in a focus area the air quality positive expectation is more likely to be applied. Check both at the outset, because the designation changes the scope of the assessment and therefore the fee and the programme.
Construction and conditions
London's controls on non-road mobile machinery apply to construction plant above a power threshold, with minimum emission stage standards and a registration requirement. Build that into the construction phase chapter and into the tender documents, because the obligation falls on the contractor and the condition falls on the applicant.
Expect conditions covering a dust management regime, the non-road machinery standards, the emission standard for any combustion plant, and in some cases a verification report before occupation confirming that the plant installed matches the plant assessed.
An illustrative case: an outer London scheme of 180 flats with communal gas boilers and 0.5 parking spaces per unit. The first assessment exceeded both benchmarks. Switching to air source heat pumps removed the building emissions limb, and reducing parking to 0.25 spaces with a car club bay brought transport emissions below the benchmark. No off-site contribution was needed, and the energy strategy improved at the same time.
Enter your postcode on PlanScope to see which reports a London scheme is likely to need.
PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. For specialist technical reports, qualified professional input may be required.
Frequently asked questions
What does air quality neutral mean in the London Plan?
Policy SI 1 requires development to emit no more nitrogen oxides and particulate matter than the published benchmarks for a development of that type, size and location. It is a comparison, not a zero emissions test. The assessment has two limbs, building emissions from combustion plant and transport emissions from the trips generated.
Which schemes have to be air quality positive?
Larger-scale development, including masterplans, and schemes in Air Quality Focus Areas or likely to be used by people vulnerable to poor air quality. The output is an air quality positive statement covering the location of sensitive uses, massing and street form, ventilation intakes, green infrastructure and the movement strategy, prepared early enough to shape the masterplan.
Does going all-electric pass the neutral test?
It removes most of the building emissions limb, because the benchmark compares combustion emissions on site and heat pumps produce none. The transport limb still has to be passed, which usually means limiting car parking and securing that limit by condition or obligation. Most compliant schemes do both.
Can green walls count as air quality mitigation?
They are worth providing for several reasons, and they are weak as quantified air quality mitigation. Claiming a specific pollutant removal from planting will be challenged unless the method is published and the figures defensible. Treat green infrastructure as a benefit alongside the assessment rather than as the way of passing it.
What applies to construction plant in London?
London operates emission standards for non-road mobile machinery above a power threshold, with minimum engine stage requirements and a registration duty. The obligation falls on the contractor in practice but the planning condition binds the applicant, so put the requirement into the construction phase chapter and into the tender documents.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.