Fine particulate matter — PM2.5 — has moved to the centre of air quality planning. New legally binding targets under the Environment Act, plus interim planning guidance published by Defra, mean that air quality assessments in 2026 increasingly have to show how a development affects PM2.5, not just nitrogen dioxide. This article explains what PM2.5 is, what the new targets require, and what it all means for your planning application.
What is PM2.5 and why do planners care?
PM2.5 is airborne particulate matter 2.5 micrometres in diameter or smaller — small enough to penetrate deep into the lungs and enter the bloodstream. It comes from combustion (traffic, domestic burning, industry) and from secondary chemical reactions in the atmosphere. Because there is no safe threshold below which it stops causing harm, PM2.5 is treated as one of the most significant environmental risks to public health, which is why it now features so heavily in air quality assessments for planning.
The two Environment Act PM2.5 targets
The Environmental Targets (Fine Particulate Matter) (England) Regulations 2023 set two targets to be met across England by 2040:
- An annual mean concentration target of 10 µg/m³ — roughly half the previous 20 µg/m³ objective, and aligned more closely with World Health Organization guidance.
- A population exposure reduction target of a 35% cut in average population exposure to PM2.5, measured against a 2018 baseline.
Together these push both the worst hotspots and the general background downward — a different emphasis from the older objective-based system that focused on discrete exceedance locations. This is a broader ambition than the familiar Air Quality Management Area framework, which targets specific declared areas.
Interim planning guidance: what changed
Defra published interim planning guidance on considering the Environment Act PM2.5 targets in planning decisions. The key points for applicants are:
- The targets apply to all ambient (outdoor) air across England, whether or not a monitor is present — so an assessment cannot simply rely on the nearest monitoring station.
- The guidance applies to developments that have the potential to emit PM2.5 or that introduce people sensitive to it (new homes, schools, care settings).
- Evidence should be set out within the air quality assessment, either as part of an Environmental Statement for EIA development or as a standalone AQA where EIA is not required.
What this means for your air quality assessment
In practice, assessments now weigh PM2.5 alongside NO₂, PM10 and NOx, comparing predicted concentrations against the 10 µg/m³ target and considering the scheme's contribution to population exposure. The assessment still follows established methods — the EPUK/IAQM land-use planning guidance and Defra's LAQM.TG(22) technical guidance — but frames the results against the tighter PM2.5 ambition. For London schemes, this dovetails with London Plan Policy SI 1 on air quality neutral and air quality positive development. Where impacts are significant, mitigation such as low-emission design, planting and ventilation strategy comes into play.
Do you need an air quality assessment for a smaller scheme?
Not every application needs a detailed assessment, but the trend is towards more scrutiny, not less. A simple screening exercise usually decides the level of work required: it looks at whether the site introduces new sensitive receptors (homes, schools, care settings) into an area of poor air quality, whether the development materially increases traffic, and whether demolition or earthworks will generate dust. If the answers are all negative, a short air quality statement may suffice; if any are positive, a fuller assessment is expected. Construction-phase dust is a common trigger in its own right — we cover this in our guide to construction dust assessments, which follows the IAQM dust guidance (v2.2, 2024).
Mitigation and exposure
Where a scheme places new residents close to a busy road or within an AQMA, the assessment considers exposure — the risk of introducing people to concentrations near or above the objectives. Good design reduces that exposure: setting habitable rooms and balconies away from the pollution source, providing mechanical ventilation with filtration, orienting the layout to create sheltered courtyards, and using green infrastructure to help disperse and absorb pollutants. Demonstrating these measures is often what turns an air quality objection into a manageable planning condition.
How Fortress Associates can help
Fortress Associates prepares automated, site-specific air quality assessments for planning applications across every UK local authority, and the report is free. We use live official datasets at the point of report creation — Defra background maps, AQMA boundaries, monitoring data and DfT traffic counts — and assess NO₂, PM2.5, PM10 and NOx against the relevant objectives and guidance. Begin on our air quality assessment page, contact us via the contact page, or explore our wider services.
Sources & further reading
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