Air quality neutral assessment for London schemes

Air quality neutral is a London requirement, not a national one. Policy SI 1 of the London Plan requires major development proposals to be at least air quality neutral, and larger-scale schemes to go further and demonstrate an air quality positive approach. If your site is outside Greater London, none of this applies and the assessment follows national policy and the joint IAQM and Environmental Protection UK criteria instead.

Inside London it is a validation matter. Boroughs ask for the calculation, and a submission without it goes back.

What air quality neutral means

The test compares the emissions your development is expected to produce against benchmark emissions for a development of the same type and size. Two streams are assessed separately: building emissions, mainly from heating and hot water plant, and transport emissions, from the vehicle trips the development generates.

For each stream, and for each of two pollutants, nitrogen oxides and fine particulate matter, the calculation produces a figure for the proposed development and a figure for the benchmark. Where the proposed figure is at or below the benchmark, that stream is neutral. Where it is above, the difference has to be mitigated, and where mitigation cannot close the gap, offset.

The neutrality test is about emissions produced, which is a different question from the concentrations people breathe. A scheme can be air quality neutral and still need an Air Quality Assessment of exposure, because it sits in an Air Quality Focus Area or introduces receptors into an Air Quality Management Area.

Where the benchmarks come from

The Greater London Authority publishes the benchmarks in London Plan Guidance, expressed per square metre of gross internal area per year for building emissions and by land use for transport emissions. Land use classification drives everything, so the schedule of areas by use is the first thing a reviewer checks.

Two points matter more than the arithmetic.

The benchmarks have been revised. Guidance published in 2023 replaced an earlier method that had been in use since 2014, and consultants still occasionally submit calculations on the older basis. State the guidance version and its date on the first page of the calculation.

And the benchmark is not a policy target you can negotiate. It is a comparator derived from a defined reference case. Arguing that your scheme should be compared against something else is a losing position unless the land use has no published benchmark at all, in which case agree the approach with the borough and the GLA before you calculate.

The building emissions calculation

This one follows the energy strategy. The inputs are the gross internal area by land use, the heating and hot water system type, its rated emission performance and the assumed annual heat demand.

The result is largely decided by the plant selection. A scheme heated entirely by air source heat pumps produces no on-site combustion emissions and passes comfortably. A scheme with gas boilers, or with a gas-fired combined heat and power unit sized for a communal network, has to demonstrate compliance with the emission limits GLA guidance sets for that plant, and even compliant plant may exceed the benchmark at scale.

Take the current emission limits from the guidance in force rather than from an older supplementary planning document, because the figures have changed. Manufacturer test data at the specified conditions is the evidence, and a datasheet quoting performance at different reference conditions will be queried.

Biomass is effectively closed off. The London Plan's position on biomass in an urban air quality context is clear, and a scheme proposing it invites an objection from the borough and the GLA together.

The transport emissions calculation

This one follows the transport work. Trip generation for the proposed use, converted into vehicle kilometres, then into emissions using published vehicle emission factors, then compared against the transport benchmark for the same land use and area.

The inputs are where disputes arise. Trip rates should come from the transport assessment rather than from a different assumption, and the mode share should match the Travel Plan. A calculation assuming 15 per cent car mode share while the transport chapter assumes 25 per cent will be spotted.

Car-free and car-capped schemes do well here, which is the policy intention. So does servicing consolidation, and so does a delivery and servicing strategy that reduces peak vehicle movements.

Air quality positive for larger schemes

Above the air quality neutral requirement sits an air quality positive expectation for large-scale development, including masterplans and schemes in Opportunity Areas. This is a design process requirement rather than a calculation.

An air quality positive statement is meant to be produced early, before the layout is fixed, and to show how the proposals improve local air quality and reduce exposure. The moves are architectural rather than technical: building massing that avoids street canyon effects, green infrastructure placed where it helps rather than where it looks good on a plan, sensitive uses such as nurseries and playgrounds located away from the worst frontages, and servicing routed off the busiest streets.

Produced after the design is fixed, it becomes a justification document and reads like one. The GLA notices.

Evidence the GLA expects to see

A submission that survives review contains:

• the guidance version used and its publication date
• a floor area schedule by land use, tying to the drawings
• the building emissions calculation with plant performance evidence at stated reference conditions
• the transport emissions calculation with trip rates traceable to the transport assessment
• benchmark and proposed figures side by side, for nitrogen oxides and particulate matter, for both streams
• where a stream exceeds the benchmark, the mitigation applied and any residual offset
• for larger schemes, the air quality positive statement and the design decisions it produced

Where an offset payment is calculated, set out the method and the damage cost basis rather than presenting a total.

Why submissions get sent back

Five reasons account for most of them. Using superseded benchmarks. A floor area schedule that does not reconcile with the area schedule elsewhere in the application. Transport inputs inconsistent with the transport assessment. No evidence of plant emission performance, only a statement of intent. And an air quality positive statement submitted as a retrospective narrative on a large site.

There is a sixth that is harder to fix: treating air quality neutral as the whole air quality chapter. Boroughs also expect the exposure assessment, construction dust, and where relevant a Noise Impact Assessment and a Ventilation and Extraction Statement for any commercial kitchen. Neutrality answers one policy, not the chapter.

Illustrative example: a 210-unit build to rent scheme in an inner borough, with a ground floor food and beverage unit. The first submission used gas boilers with a small combined heat and power unit and exceeded the building benchmark for nitrogen oxides. Replacing the plant with air source heat pumps and electric hot water removed on-site combustion entirely, took the building stream below benchmark, and simplified the extract strategy for the commercial unit as well.

Councils usually expect a suitably qualified author for this work, and professional review before submission is strongly advised. Browse the full set of report types to see what a London major application typically needs.

This is general guidance about London policy, not legal advice; check the current London Plan Guidance and confirm the position with the borough or a qualified professional before relying on it. 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.