A scoping checklist for an air quality assessment

Scope an air quality assessment by answering two separate screening questions before anyone models anything. Does the construction phase need a dust risk assessment, and does the operational phase exceed the traffic or exposure screening criteria that trigger modelling. Most minor and medium schemes need the first and not the second, and the appropriate output is a dust assessment and a mitigation schedule rather than a dispersion model. Air quality assessment scoping goes wrong when a developer commissions a full modelling exercise for a scheme that needed four pages, or submits four pages for a scheme that needed the model.

Agree the scope with environmental health first. It costs an email.

Deciding whether an assessment is needed at all

Three triggers, any one of which brings air quality into the submission.

The scheme generates or attracts enough vehicle movements to change concentrations at existing receptors. The scheme introduces new receptors into an area of existing poor air quality, typically within or adjoining an Air Quality Management Area. Or the scheme introduces a new emission source, such as a biomass boiler, a combined heat and power plant, a standby generator or a commercial kitchen extract.

Add a fourth in practice: the local validation list. Some councils require an air quality assessment for any major application, or for any development within a declared management area, regardless of the technical screening. Check the validation checklist before deciding the technical answer, because the validation requirement is the one that stops the application being registered.

Where the scheme is caught, the Air Quality Assessment is the document, and the Institute of Air Quality Management guidance on land-use planning and on construction dust sets the method councils expect.

Construction phase dust risk screening

Nearly every scheme with groundworks needs this, and it costs little to do properly.

The method assesses four activities separately: demolition, earthworks, construction and trackout, which is dust carried onto the public highway by vehicles leaving the site. For each activity it combines the scale of the activity with the sensitivity of the surrounding area, derived from the number and proximity of human and ecological receptors, to produce a risk category.

The output is a risk category per activity, and the mitigation schedule follows from it. That schedule is what gets conditioned, so write it as site rules a contractor can follow: wheel washing, damping, sheeting, hoarding heights, the position of the site compound relative to the nearest housing, a named site contact for complaints, and recording. It belongs alongside the construction management plan checklist for a tight site rather than being duplicated in both documents.

Operational traffic screening and the trip thresholds

For operational road traffic the screening is based on the change in traffic flows on affected links, usually expressed as a change in annual average daily traffic, with lower thresholds inside a management area than outside it and lower thresholds again for heavy vehicles.

Those indicative figures come from the professional guidance rather than from legislation, and they are indicative. Where the predicted change sits close to a threshold, model it rather than arguing about it. The cost difference is small and the appeal risk is not.

What the screening needs as input is the trip generation from the transport work, so the air quality scoping cannot precede the Transport Assessment or Transport Statement. Using a different trip rate in the two documents is a visible inconsistency, and reviewers compare them.

Car park size is a separate screening consideration, because a large car park concentrates cold starts and idling in one place.

Receptor identification and sensitivity

Identify receptors by where people are exposed for the averaging period of the relevant objective, which is the step most often done loosely.

The annual mean objective for nitrogen dioxide and particulate matter applies where people are present for the annual average, so facades of residential properties, schools, hospitals and care homes count. It does not apply at the kerbside of a road where nobody lives, or in the middle of a car park. The short-period objectives apply where exposure for that shorter period is realistic, including pavements and gardens in some cases.

List each receptor with a reference, an address or description, the height of the assessed point, the distance from the source and the relevant objective. Then include the proposed receptors in the scheme itself, at the worst-case facade and the worst-case floor, because the exposure of future occupants is a material consideration and a scheme that models only existing neighbours has answered half the question.

Ecological receptors need separate treatment where a designated site lies within the relevant distance of a road whose flows change, because nitrogen deposition on a sensitive habitat has its own criteria and brings the Preliminary Ecological Appraisal into the conversation.

Baseline data: monitoring, diffusion tubes and modelled background

The baseline should use local measured data in preference to anything modelled.

Sources in order of preference: continuous automatic monitoring stations operated by the council or the national network, the council's diffusion tube network as reported in its annual status report, and the national mapped background concentrations for the relevant grid square where no local data exists. Diffusion tube data needs the bias adjustment factor applied and the annualisation where a full year is not available, and a report that quotes raw tube results without either has overstated or understated the baseline.

State the year of the data and the trend. Concentrations have generally been falling, so a baseline from several years ago is conservative for the existing case and may be wrong for the assessment year. Use the council's most recent annual status report and cite its year.

Assessment methods and model selection

Where modelling is required, the scoping note should say which model, which meteorological data, which emission factors and which verification approach.

The choices that need stating: the dispersion model and version, the meteorological station and year or years used, the emission factor database and version, the treatment of street canyons where relevant, the road source geometry and how junctions are represented, and the model verification against local monitoring with the adjustment factor derived and justified. Verification is the step that separates a defensible assessment from an arithmetic exercise, and an unverified model result should be treated with caution.

For point sources such as boilers or generators, the stack height assessment and the building downwash treatment matter more than the road modelling detail.

Mitigation, offsetting and damage cost payments

Mitigation first, then offsetting, and the order is not negotiable in most local guidance.

Mitigation means designing the emissions out: lower-emission heating, electric vehicle charging provision, travel planning to reduce car trips, locating ventilation intakes away from sources, and site layout that keeps habitable rooms off the most exposed facade. Where residual emissions remain, some councils require a damage cost payment calculated by the published damage cost approach, secured through a planning obligation and spent on measures in the local air quality action plan.

Check whether the council has an adopted air quality supplementary planning document with its own calculation method, because where one exists it governs, and the figure it produces can be a meaningful cost line that belongs in the appraisal early rather than at committee.

Agreeing scope with environmental health first

Write a one-page scoping note and send it to the environmental health officer before commissioning the work.

Put in it the development description and quantum, the construction programme outline, the predicted change in traffic flows on the affected links with the source of those figures, the proposed emission sources, the receptors identified, the baseline data proposed, and the assessment method proposed for each phase. Ask for written agreement or comments.

A scoping note that comes back agreed removes most of the argument at determination stage, and where it comes back with a request for more, you have learned it before the fee was spent rather than after. The same discipline applied before submission is covered in an internal quality check before anything leaves the office.

An air quality assessment is a report councils expect a suitably qualified author to prepare, and professional review is strongly advised. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.