Air Quality Neutral and Air Quality Positive explained

Air Quality Neutral and Air Quality Positive are two separate London Plan requirements that applicants routinely merge into one document and then fail both. Air Quality Neutral is a numerical test: the emissions from your building and from the transport it generates must not exceed published benchmarks for that type and size of development. Air Quality Positive is a design process applied to large-scale schemes and masterplans, asking how the layout, massing and movement strategy improve exposure rather than merely avoid making it worse. One is arithmetic. The other is design reasoning, and it has to happen early.

What air quality neutral requires

The London Plan expects development proposals to be at least air quality neutral. In practice that means demonstrating that emissions of oxides of nitrogen and particulate matter do not exceed the benchmarks published in the Mayor's air quality neutral guidance.

Two streams are assessed separately. Building emissions cover combustion plant serving the development, principally boilers and any combined heat and power or standby generation. Transport emissions cover the vehicle movements the development generates.

Both are compared against benchmarks expressed per square metre of floorspace by land use, so the scale and mix of the scheme set the target before any design decision is made. Take the current benchmark figures from the guidance itself, since the methodology and the numbers have been revised and an assessment using superseded values will be sent back.

The building emissions side has become simpler to pass as gas plant disappears from new schemes. A development with heat pumps and no combustion plant has very low building emissions, which shifts the burden onto the transport figure.

How the benchmarks work

The calculation is mechanical once the inputs are fixed, and the inputs are where the work is.

For building emissions you need the plant schedule, the rated thermal input of each item, the fuel, the emission rate in the manufacturer's data, and the assumed hours of operation. Standby generators are often omitted and should not be, because boroughs ask about them.

For transport emissions you need trip generation for the completed development, the vehicle mix, trip lengths and an emission factor set. The trip figures must be the same ones used in the Transport Assessment, and a mismatch between the two documents is the fastest way to lose an air quality argument.

Where the scheme exceeds a benchmark, the sequence is to reduce emissions at source first, then to mitigate, and only then to discuss whether the borough accepts any form of offsetting. Not all of them do, and the position varies, so ask rather than assume.

Where air quality positive applies

Air Quality Positive is aimed at masterplans and large-scale development, and it is a statement produced early in design rather than a calculation produced at submission.

It asks how the proposal improves air quality outcomes for people. The moves that matter are spatial: locating homes, schools and play space away from the most polluted frontages, using building form to avoid street canyon effects, orienting habitable rooms and ventilation intakes away from traffic, placing green infrastructure where it separates receptors from sources, and designing the movement strategy so the scheme generates fewer vehicle trips in the first place.

The document should be produced at concept stage and referenced in the design evolution narrative. An air quality positive statement written after the masterplan is fixed can only describe what happened to be designed, and reviewers can tell the difference immediately.

Coordinate it with the Travel Plan, because trip reduction is the single measure that improves both the neutral calculation and the positive narrative.

Evidence and modelling the boroughs expect

Beyond the benchmarks, a full Air Quality Assessment is normally needed where the site is in an air quality management area, where the development is large, or where sensitive receptors are being introduced close to a busy road.

The expected content follows the Institute of Air Quality Management and Environmental Protection UK guidance on planning and air quality.

• Baseline concentrations from Defra background maps, borough monitoring data and, where the site is sensitive, site specific diffusion tube monitoring.
• Dispersion modelling of the relevant road links and any point sources, with the model named and verified against local monitoring.
• Assessment of exposure at proposed receptors, including balconies, gardens and play areas rather than facade points alone.
• A construction phase dust assessment using the standard risk categories, feeding into the Construction Management Plan.
• Cumulative assessment with committed development.

Model verification is where assessments are weakest. An unverified model applied to a canyon street with high kerbside concentrations will underpredict, and an environmental health officer who monitors that street knows it.

Mitigation that gets accepted

Source reduction first. No combustion plant, or the lowest emission plant where combustion is unavoidable, with flue heights and termination points designed rather than defaulted.

Exposure reduction second. Setting back the building line, raising habitable rooms above ground floor on the most polluted frontage, single aspect units facing away from the road, mechanical ventilation with filtration and intakes at roof level, and green infrastructure used as a barrier rather than as decoration.

Trip reduction third, through parking restraint, car club provision, cycle parking quality and a monitored travel plan. This is where the Energy Statement and the air quality work overlap, since the move away from gas serves both.

Construction phase controls are usually dealt with by condition: dust suppression, wheel washing, a nominated responsible person, and compliance with the non-road mobile machinery emission standards that apply in London, including registration of qualifying plant.

Air quality management areas and focus areas

Boroughs declare air quality management areas under the Environment Act 1995 where objectives are not being met, and they publish action plans. Every London borough has declared at least part of its area, so being inside one is not by itself unusual and does not prevent development.

Air Quality Focus Areas are a separate Greater London Authority designation covering locations with both high concentrations and human exposure. A site in a focus area attracts closer scrutiny, and the air quality positive expectation is more likely to be applied.

Check both at the outset, along with the borough's own air quality supplementary planning document where one exists. The local document often sets requirements beyond the London Plan, including monitoring obligations and, in some boroughs, a damage cost payment approach.

Why statements get sent back

Four reasons account for most of them.

Benchmarks quoted from a superseded version of the guidance. Trip generation figures that differ from the transport documents. Standby generators or commercial kitchen extract omitted from the building emissions calculation. And an air quality positive statement that is a description of the submitted scheme rather than a record of design decisions.

The fourth is the one that cannot be fixed at submission stage. If the masterplan puts the school on the trunk road frontage, no amount of writing improves it. That is why this work belongs in the first month of design rather than the last.

This is general guidance, not legal advice. Check the current London Plan guidance and your borough's requirements before relying on it.

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