Air quality assessment or odour assessment: which is needed

Whether you need an air quality assessment or odour assessment comes down to what the environmental health officer is worried about. Air quality work deals with measurable pollutants against published objectives, mainly nitrogen dioxide and particulate matter, and it is triggered by Air Quality Management Area designation or by the traffic and combustion plant a scheme generates. Odour work deals with something people smell, which has no statutory objective, and it is triggered by the process: cooking, brewing, waste handling, agriculture.

A restaurant in a town centre Air Quality Management Area can need both. A takeaway in a village with a clean air record usually needs only the odour side. Scoping the right one saves a month.

Pollutants measured against objectives

Air quality assessment is arithmetic against numbers that exist. The local air quality management regime under Part IV of the Environment Act 1995 requires councils to review air quality against national objectives and to designate an Air Quality Management Area where those objectives are not met.

The objectives that matter for most planning work are the nitrogen dioxide annual mean of 40 micrograms per cubic metre, the nitrogen dioxide one hour mean of 200 micrograms per cubic metre not to be exceeded more than 18 times a year, and the PM10 annual mean of 40 micrograms per cubic metre with a 24 hour mean of 50 not to be exceeded more than 35 times. Fine particulate matter has its own targets, tightening over time.

So the question an Air Quality Assessment answers is concrete. What are concentrations now at relevant receptors, what will they be with the development, and does the change matter against those figures.

When designation triggers assessment

Three triggers account for most air quality work on small commercial schemes.

The first is location. A development inside or adjacent to an Air Quality Management Area attracts scrutiny, particularly where it introduces new receptors such as flats or a nursery into an area already exceeding an objective.

The second is traffic. Where a scheme changes vehicle flows on roads within or near an Air Quality Management Area by more than a screening threshold, the assessment is expected. The industry criteria used by most consultants are lower inside a designated area than outside it, which is why a modest change of use on a high street can trigger work that the same scheme would avoid two miles away.

The third is combustion. Biomass boilers, combined heat and power units, standby generators and large gas plant introduce a point source, and the council will want a stack height calculation and a screening assessment.

Construction dust sits inside air quality work rather than alongside it. A dust assessment following the published industry method classifies the site by risk for demolition, earthworks, construction and trackout, and produces a mitigation schedule that is then conditioned. Even a small scheme in a sensitive area usually needs the classification step.

How odour is assessed and what limits it

Odour has no objective in the sense that nitrogen dioxide has one. Assessment works through the character of the exposure rather than through a single number.

Practitioners use the FIDOL factors: frequency of the exposure, intensity of the odour, duration of each episode, offensiveness of the odour character, and the sensitivity of the location. A faint sewage odour twice a year in an industrial estate and a strong frying odour every evening above a flat are different propositions, even at similar concentrations.

Where modelling is justified, an Odour Assessment uses dispersion modelling with source strengths expressed in European odour units, sometimes measured by dynamic olfactometry to the relevant European standard, compared against benchmark levels that vary with how offensive the odour is. That is expensive work, proportionate for a waste transfer station or an intensive livestock unit rather than for a pizza shop.

For a commercial kitchen the assessment is usually a risk-based exercise following the national guidance on odour and noise from commercial kitchen exhaust systems. It scores the risk from the cooking type, the size of the kitchen and the proximity of receptors, then specifies an abatement package to match.

The kitchen extract case in detail

Most odour disputes in planning are about extract systems, and most of them are decided on four details.

The termination point. Discharge should normally be at roof level, above the ridge or the highest point of the building, away from openable windows and air intakes, including those of neighbours.

The efflux velocity. A high discharge velocity, commonly at least 15 metres per second, carries the plume clear of the building rather than letting it roll down the facade.

The abatement train. Grease filtration first, then carbon filtration, electrostatic precipitation or ultraviolet treatment sized to the cooking type. Char grilling and wok cooking need far more than a sandwich bar.

The maintenance regime. Carbon media exhaust, and a system that is not maintained fails within months. Councils condition maintenance logs for exactly this reason.

A Ventilation and Extraction Statement covering those four points, with a duct route drawn on the elevations, answers the officer's question directly.

Which consultee comments on each

Both usually go to the environmental health officer, who may hold separate air quality and pollution control functions within the same team.

The Environment Agency comments where the activity needs an environmental permit, which covers larger waste, intensive farming and industrial installations. It does not comment on a restaurant extract.

Neighbours comment on odour far more than on air quality, because odour is perceptible and nitrogen dioxide is not. That asymmetry matters at committee: an odour objection arrives with lived experience attached, while an air quality objection arrives with a number that members find hard to weigh.

Mitigation and the conditions that follow

Air quality mitigation on a small scheme is usually a schedule: electric vehicle charging provision, low emission boilers meeting a stated emissions standard, a construction dust management scheme, and sometimes a financial contribution to the council's air quality action plan where the local plan provides for it.

Odour mitigation is equipment. The condition normally requires a scheme of odour control to be submitted and approved before the use starts, installed before first use, and maintained thereafter in accordance with an approved regime.

Read the wording. A condition requiring approval of the odour scheme before the use starts will delay opening if you leave it until the fit-out, and a landlord's rent-free period rarely accommodates a two month discharge application.

Scoping both for a food business

For a new restaurant or takeaway, work through five questions in order. Is the site in or next to an Air Quality Management Area. Does the scheme change traffic flows materially. Is there combustion plant beyond a domestic scale boiler. What is the cooking type and the nearest sensitive receptor, measured in metres and in vertical separation. And is there an existing extract system, and does it terminate where it should.

Answer those and the scope writes itself. Most town centre food businesses land on an extraction statement plus an odour risk assessment, with air quality work only where designation or plant brings it in.

The same scoping logic applies to noise from plant and customers, where the choice of method matters as much as it does here. The comparison of BS 4142 and ProPG methods covers that ground, and a Noise Impact Assessment frequently sits alongside the odour work in the same submission.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. Councils usually expect air quality and odour assessments to be prepared by a suitably qualified author, 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.

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