If you are developing in London, the phrase "air quality neutral" will appear on your validation checklist sooner or later. Under London Plan Policy SI 1, development proposals must be at least air quality neutral and must not lead to any further deterioration of existing poor air quality. This article explains what that means in practice, how the benchmarks work, and what your air quality assessment needs to show.
What does air quality neutral mean?
Being air quality neutral means a development does not add to pollutant emissions in the surrounding area beyond an agreed benchmark. The Greater London Authority sets maximum allowable emissions of nitrogen oxides (NOx) and particulate matter, based on the size and use class of the proposal. A scheme calculates its likely emissions from two sources — the buildings themselves and the transport it generates — and compares them against those benchmarks.
If a scheme comes in at or below the benchmark, it is air quality neutral. If it exceeds the benchmark, the applicant must either redesign to cut emissions or, where the guidance allows, offset the shortfall. The policy applies across London and sits alongside the national picture set by the Environment Act PM2.5 targets.
Building and transport emissions
The assessment splits into two benchmarks:
- Building emissions — mainly from any combustion plant serving the development, such as boilers or combined heat and power. The GLA guidance replaced the older PM10 benchmark with PM2.5, reflecting stronger public-health evidence. In practice the building PM2.5 benchmark is effectively zero, which means biomass boilers and most on-site combustion are very hard to reconcile with air quality neutral unless limited to genuine emergency or standby plant.
- Transport emissions — from the vehicle trips the development generates. Reducing car dependency, providing cycle infrastructure and locating density near public transport all help a scheme meet the transport benchmark.
Because the building benchmark now effectively rules out combustion for particulates, air quality neutral pushes schemes towards electric heating and heat pumps — one of several points where air quality policy and your energy strategy reinforce each other.
Air quality positive — the next step for large sites
For major, masterplan-scale development the London Plan goes further, asking schemes to be air quality positive. Rather than simply not making things worse, an air quality positive approach requires designers to show what measures have been taken to maximise the benefits to local air quality — through layout, landscaping, ventilation design and the location of habitable rooms away from the most polluted frontages. The GLA has published dedicated air quality neutral and air quality positive guidance to support Policy SI 1, and larger applications are expected to engage with both.
What your application needs to demonstrate
To satisfy a London borough on Policy SI 1, an application generally needs to:
- Calculate building and transport emissions and compare them to the current GLA benchmarks.
- Show the heating and energy strategy avoids combustion sources that would breach the PM2.5 benchmark.
- Consider exposure — where new residents will live relative to busy roads and existing poor air quality. Our note on Air Quality Management Areas explains why exposure matters.
- Set out mitigation, and for major schemes, the air quality positive measures designed in.
Getting this right early avoids a late redesign. A heating strategy chosen without reference to Policy SI 1, for example, can force expensive changes when the air quality assessment is finally run.
Does air quality neutral apply outside London?
The specific air quality neutral benchmarks are a London Plan mechanism. Elsewhere in the UK, air quality in planning is governed by the National Planning Policy Framework and Planning Practice Guidance, the EPUK/IAQM land-use planning guidance and the local authority's own air quality policies, particularly inside an Air Quality Management Area. The underlying principle — do not worsen local air quality, and mitigate where you might — applies nationwide even where the SI 1 benchmarks do not.
Common questions about air quality neutral
Does every London application need to prove air quality neutral?
Policy SI 1 applies to development proposals generally, but the depth of assessment is proportionate. A minor scheme may address it briefly, while a major scheme is expected to present full building and transport emissions calculations against the GLA benchmarks.
Can a scheme offset if it exceeds the benchmark?
Where the guidance allows, a shortfall can be offset, but the expectation is that applicants first design emissions down — through electrification, reduced car dependency and better layout — and treat offsetting as a last resort rather than a default.
Why does air quality neutral effectively rule out gas boilers?
Because the building PM2.5 benchmark is effectively zero, combustion plant that emits particulates struggles to comply. Electric heating and heat pumps avoid the problem, which is why air quality and energy strategies should be decided together.
How Fortress Associates can help
Fortress Associates prepares automated air quality assessments for UK planning applications, covering every local authority. The report is free and ready in minutes, and it draws on live official datasets at the point of creation — Defra background concentration maps, AQMA boundaries, monitoring network data and DfT traffic counts. It assesses NO2, PM2.5, PM10 and NOx and follows the IAQM dust guidance (v2.2, 2024), the EPUK/IAQM land-use planning criteria, Defra LAQM.TG(22), the NPPF and, for London sites, London Plan Policy SI 1. See our services or contact us to discuss your scheme.
Sources and further reading
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