Applicants often ask why an air quality assessment is judged against the UK’s legal limits rather than the stricter World Health Organization (WHO) guidelines they have read about. It is a fair question — the gap between the two is large. This guide sets out how the WHO air quality guidelines compare with UK objectives, and which numbers your planning application actually has to satisfy in 2026.
What the WHO 2021 guidelines say
In 2021 the WHO tightened its global air quality guidelines significantly. The headline annual-mean guideline values are now:
- Nitrogen dioxide (NO₂): 10 µg/m³
- Fine particulate matter (PM2.5): 5 µg/m³
These are health-based recommendations reflecting evidence that there is no safe threshold for particulate pollution. They are guidelines, not law — the WHO has no power to set national standards.
What the UK objectives say
UK planning works to the national air quality objectives and legal limits, which are considerably higher:
- NO₂: 40 µg/m³ annual mean
- PM10: 40 µg/m³ annual mean
- PM2.5: a new England target of 10 µg/m³ annual mean to be met by 2040, plus a population-exposure reduction target of 35% against 2018 levels, both set under the Environment Act 2021
So for NO₂ the UK objective is four times the WHO guideline, and for PM2.5 the UK’s 2040 target is double the WHO value. We break the pollutants themselves down in NO₂, PM10, PM2.5 and NOx explained, and cover the Environment Act targets in detail in our PM2.5 targets post.
Which values does an air quality assessment use?
For a planning application, the answer is clear: your air quality assessment is assessed against the UK objectives, not the WHO guidelines. Assessors follow the joint EPUK and IAQM land-use planning guidance, which uses the UK objectives as the benchmark for judging whether a development’s impact is significant, together with Defra’s technical guidance LAQM.TG(22) and background concentration maps. The WHO guidelines are not the pass/fail line in England.
So why do the WHO values matter at all?
They matter for three reasons. First, direction of travel: the Environment Act target and the UK’s long-term ambition are pulling standards toward the WHO figures, and future guidance is likely to tighten. Second, good design: schemes that introduce new residents to areas already close to the UK limits benefit from designing well inside them — the WHO values are a useful stretch target. Third, London policy: the London Plan’s air quality expectations, including the air quality neutral and air quality positive approaches, push schemes to minimise emissions rather than simply scrape under the legal limit. We explain that framework in Air Quality Neutral and London Plan Policy SI 1.
Practical implications for applicants
The takeaway is not to design merely to avoid breaching 40 µg/m³ of NO₂. Where your site sits in or near an Air Quality Management Area, or beside a busy road, exposure of future occupiers is a genuine planning issue — the shift we describe in our post on new homes near busy roads. Sensible layout, ventilation strategy and setback from traffic all help you demonstrate that a scheme is acceptable, and give you headroom as standards tighten toward the WHO benchmarks.
When is an air quality assessment actually required?
Not every application needs a full assessment against these values. The trigger is usually the scale and location of the scheme. A material assessment is normally expected where a development introduces significant new traffic, brings new residents into an area already close to the objectives, sits within or adjacent to an Air Quality Management Area (AQMA), or involves demolition and earthworks that generate dust. We explain the AQMA test in what an AQMA means for your application.
Where the impact is likely to be small, a shorter air quality statement or a screening assessment may be enough to satisfy the validation requirement — but that screening still has to be evidenced against the UK objectives and background concentration data, not simply asserted. Construction-phase dust is assessed separately using the IAQM dust guidance (v2.2, January 2024), and mitigation such as wheel washing, damping down and hoarding is set out in a construction environmental management plan. Getting the screening judgement right at the outset saves an authority coming back later to ask for a full study.
How Fortress Associates can help
Fortress Associates produces automated air quality assessments for UK planning applications, using live official datasets — Defra background maps, AQMA boundaries and DfT traffic data — and following EPUK/IAQM criteria and Defra LAQM.TG(22). The report is free and ready in minutes, and it screens your NO₂, PM2.5 and PM10 concentrations against the UK objectives for you. See our services or get in touch.
Sources & further reading
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