Air Quality Assessment outline for residential in an AQMA

An air quality assessment outline for residential development inside an Air Quality Management Area has to answer two questions in one document: will the new occupiers be exposed to concentrations above the objectives, and will the development make conditions worse for people already there. Most reports answer the second at length and the first in a paragraph. Officers in an AQMA read the exposure section first.

An AQMA is declared by the authority under Part IV of the Environment Act 1995 where the air quality objectives are not being met. Declaring it triggers an action plan, and the action plan is the policy document your assessment has to engage with, alongside the local plan policy and the national guidance.

Which route the assessment takes

Screen before you model. The screening question is whether the development is capable of having an air quality effect, judged on the change in traffic flows, the introduction of exposure, and any combustion plant.

Three outcomes follow. A small scheme with no plant and a trivial traffic change inside an AQMA still needs an exposure assessment, because the receptors are new. A scheme with a material traffic change needs dispersion modelling of the affected road network. A scheme with biomass or combined heat and power needs a plant emissions assessment as well.

Say which route you have taken and why, with the screening criteria you applied and their source. A report that starts with model outputs and never explains why modelling was the right level of detail invites a request for further information.

Baseline monitoring and background data

The baseline section has to be built from three sources and should say so plainly.

• The authority's own monitoring: diffusion tube and automatic monitor data from the annual status report, with site classifications and distances from the kerb. Use the most recent full calendar year and state it.
• National background maps for the relevant pollutant and year, giving the non-road contribution at the grid square containing the site.
• Bespoke monitoring where the authority has no monitor close enough. Diffusion tubes need a minimum period, with bias adjustment and annualisation where a full year is not available, and the method should follow the national local air quality management technical guidance.

State the objectives you are assessing against and their basis. For nitrogen dioxide the annual mean objective is 40 micrograms per cubic metre with a one hour mean of 200 not to be exceeded more than 18 times a year. For PM10 the annual mean is 40 with a 24 hour mean of 50 not to be exceeded more than 35 times. PM2.5 sits under the 2010 regulations with a long term England target set under the Environment Act 2021. Check the current figures before you publish, because the PM2.5 position has moved.

Construction phase dust risk

Construction is assessed qualitatively using the established dust risk method, which considers four activities separately: demolition, earthworks, construction and trackout. For each, the scale of the activity is combined with the sensitivity of the surrounding area to give a risk category.

The output is not a number. It is a set of site-specific mitigation measures tied to the risk category, which then go into the construction environmental management plan and are secured by condition. Generic mitigation lists copied between reports are the most common weakness in this section. If the site has a school 30 metres downwind of the earthworks area, say so and set out what changes because of it.

Where demolition involves a building with asbestos or a former industrial process, the dust assessment and the land contamination work have to be consistent about the material being disturbed.

Operational exposure of new occupiers

This is the section that decides the application. It asks whether future residents will live in concentrations above the objectives, and it should be answered at the places people actually spend time: habitable room facades, gardens, balconies, play space and the entrance to a school or nursery within the scheme.

Present the results as predicted annual mean concentrations at identified receptor points, keyed to a drawing, floor by floor where the scheme is more than two storeys. Concentrations at first floor level on a canyon street are not the same as at ground level, and an assessment that models only the ground floor will be sent back.

Where the predicted concentration approaches or exceeds an objective, the design has to respond. Habitable rooms moved to the quiet elevation, balconies removed from the frontage, mechanical ventilation with filtration drawing from the rear at high level, and a layout that puts circulation rather than bedrooms on the exposed side. Mitigation by ventilation raises an immediate tension with overheating, because a scheme relying on closed windows for air quality cannot then rely on openable windows for cooling. Resolve that with the Overheating Risk Assessment rather than leaving the two documents to contradict each other.

Effects on existing receptors

For existing receptors the question is the change in concentration caused by the development, and the significance of that change given the absolute concentration already present.

The recognised approach expresses the change as a percentage of the objective and then applies descriptors that depend on how close the absolute concentration already is to that objective. A small absolute increase matters far more at 39 micrograms per cubic metre than at 20. Set out the descriptor table you have used and cite it.

Receptor selection needs care and honesty. Include the worst affected properties on the most affected link, not a convenient average. Where the traffic assignment sends development trips down a narrow street with a declared exceedance, model that street.

Illustrative example

A 45 unit scheme on a former garage site sits on a main road inside an AQMA declared for nitrogen dioxide. Monitoring at the kerb shows an annual mean close to the objective. Modelling predicts concentrations above the objective at first and second floor front facades, and a change at existing receptors of well under one per cent of the objective. The design response moves all bedrooms to the courtyard elevation, provides filtered mechanical ventilation with rear high level intakes, and removes front balconies. The figures here are illustrative and the outcome for any real site depends on its own monitoring and model verification.

Model inputs and verification

The credibility of the whole report rests on this section, and it should be written so another practitioner could reproduce the work.

1. Model and version, meteorological data set, year and surface roughness.
2. Traffic data: source, survey date, annual average daily flows, heavy vehicle percentage, speeds, and the with and without development scenarios including committed development.
3. Emission factors: the toolkit version and the fleet year, stated explicitly.
4. Receptor coordinates and heights.
5. Verification against local monitoring, with the adjustment factor derived for road contributions, following the national technical guidance and showing the calculation rather than just the result.
6. Uncertainty and sensitivity, including what happens if the fleet improves more slowly than projected.

An unverified model in an AQMA will be challenged. A verification that adjusts by a large factor without explanation will be challenged harder.

Mitigation and how it is secured

Separate the mitigation that reduces emissions from the mitigation that reduces exposure, because policy treats them differently.

Emissions reduction covers the travel plan, electric vehicle charging, cycle parking, car club provision, no on-site combustion for heating, and construction logistics. Exposure reduction covers layout, ventilation and glazing. Both need a securing mechanism: a condition for a scheme design, a planning obligation for a contribution or a monitored plan, and a clear statement of which is which. A Travel Plan is the usual vehicle for the emissions side, and the same discipline about naming the securing mechanism applies to a drainage strategy on a minor residential scheme.

Where the authority seeks a damage cost contribution, set out the calculation and the pollutant it relates to rather than accepting a figure without a basis.

Reporting against policy

Close the Air Quality Assessment with a conclusion that answers the policy test in the authority's own words: whether the development would give rise to unacceptable levels of exposure, whether it would prevent the action plan from achieving its objectives, and what has been secured. Avoid the phrase not significant without the descriptor that produced it.

This is general guidance, not legal advice. Check the position with your local planning authority 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, and councils normally expect air quality assessments from a suitably qualified author, so professional review is strongly advised.

Browse the 66 report types to see which documents a residential scheme in an AQMA is likely to need.