You’ll see PM2.5 and PM10 on air quality reports, planning conditions and monitoring data all the time. They sound similar, but they behave differently, come from different places, and are treated differently under UK law.

This guide explains the difference in easy way what each one is, where it comes from, what it does to your health, and what the UK rules actually say. If you’re a developer, contractor or building manager, the last few sections explain why this matters for your project.

What’s the difference between PM2.5 and PM10?

PM10 is any airborne particle smaller than 10 micrometres across. PM2.5 is any particle smaller than 2.5 micrometres. Both are types of particulate matter the technical name for tiny bits of solid and liquid floating in the air.

To picture the scale: a human hair is roughly 50 to 70 micrometres wide. PM10 is about a seventh of that. PM2.5 is around a twentieth.

One thing that trips people up: PM2.5 is technically inside PM10. Any particle under 2.5 micrometres is also under 10. So when people talk about “PM10” in practice, they usually mean the coarser particles between 2.5 and 10 micrometres.

PM2.5 vs PM10 at a glance

	PM10	PM2.5
Size	Under 10 micrometres	Under 2.5 micrometres
Common name	Coarse particles	Fine particles
Mainly comes from	Physical processes — construction dust, crushing, road dust, brake and tyre wear, pollen, sea spray	Combustion — vehicle exhaust, wood burners, industrial plant, plus particles formed in the atmosphere from NOx and SO2
How far it travels	Settles quickly, usually near the source	Stays airborne for days and can travel hundreds of miles
Where it reaches in the body	Mostly caught in the nose and throat; some reaches the upper airways	Deep into the lungs and across into the bloodstream
UK annual objective	40 µg/m³	20 µg/m³ (with a 10 µg/m³ target for England by 2040)
WHO guideline (2021)	15 µg/m³ annual	5 µg/m³ annual
Typical UK concern	Construction and demolition dust, nuisance complaints	Long-term health impact, planning policy, statutory targets

Where does each one come from?

PM10 usually comes from something physical happening material being broken, moved or disturbed. Construction and demolition are big contributors, along with crushing and grinding, quarrying, agricultural work, and dust lifted off roads.

Brake and tyre wear from traffic also produce PM10, which is why it doesn’t disappear just because vehicles go electric. Natural sources include pollen, sea spray and wind-blown soil.

PM2.5 usually comes from something burning. Vehicle exhaust, domestic wood burners and open fires, gas boilers, industrial combustion and power generation are the main ones.

A significant share is also “secondary” it forms in the atmosphere when gases like nitrogen oxides (NOx) and sulphur dioxide (SO2) react and condense into solid particles. That’s part of why PM2.5 drifts so far from where it started.

Why PM2.5 is considered more harmful

Size decides where a particle ends up in your body.

PM10 is largely trapped by the nose, throat and upper airways. It can still cause real problems coughing, wheezing, and flare ups for people with asthma or bronchitis but much of it doesn’t get far.

PM2.5 is small enough to pass through those defences, travel deep into the lung tissue, and cross into the bloodstream.

That’s why it’s linked to a much broader set of conditions: reduced lung function, worsening asthma and COPD, heart disease, strokes, and effects on pregnancy outcomes. The UK Government’s own advisory committee treats long term PM2.5 exposure as the air pollutant of most harm to health.

Ultrafine particles PM1 and PM0.1 are smaller still and likely more penetrating again, but the health evidence and the regulations remain built around PM10 and PM2.5.

What the UK rules actually say

This is where most explainers stop short, so here’s the current position.

The national objectives. Under UK air quality legislation, the annual mean objective is 40 µg/m³ for PM10 and 20 µg/m³ for PM2.5. PM10 also has a 24 hour objective of 50 µg/m³, which shouldn’t be exceeded more than 35 times a year. Scotland has adopted tighter values than the rest of the UK.

The Environment Act 2021 targets. England now has two legally binding PM2.5 targets: an annual mean concentration of no more than 10 µg/m³ by the end of 2040, and a 35% reduction in population exposure by 2040 against a 2018 baseline. DEFRA has also set interim targets for 2030. Wales has introduced its own PM2.5 target setting duty.

The WHO guidelines. The World Health Organization tightened its guidelines in 2021 to 5 µg/m³ annual mean for PM2.5 and 15 µg/m³ for PM10. These aren’t legally binding in the UK, but they’re increasingly referenced as the health based benchmark and you’ll see them cited in planning documents, particularly in London.

Why this matters if you’re developing or building

Here’s the practical bit that general air quality articles miss.

PM2.5 is now a planning consideration in England. Following DEFRA’s interim planning guidance published in October 2024, applicants are expected to show they’ve identified the key sources of PM2.5 in their scheme and taken reasonable steps to reduce emissions.

This applies to any development that would normally need an air quality assessment. Practically, that pushes schemes towards low-emission heating, fewer combustion sources, and reduced vehicle trips.

PM10 is the one your construction phase gets judged on. Construction dust is assessed as PM10 under IAQM guidance, across four separate phases demolition, earthworks, construction and trackout.

If your planning permission includes a dust condition, the dust management plan you submit will be built around controlling PM10 at the site boundary. Our guide to dust management plans for construction walks through what councils expect to see.

Both get measured differently. PM10 and PM2.5 are usually captured through air quality monitoring using automatic analysers, alongside dispersion modelling to predict future concentrations. On dusty sites, real-time PM10 monitors with agreed trigger levels are common.

A real project example

We worked on a residential scheme in the West Midlands where the site sat close to a busy A-road and backed onto existing housing. The two pollutants pulled the project in different directions.

PM2.5 was the concern for the completed development the long term exposure of future residents, driven by traffic on the adjacent road. That shaped the design: all electric heating with no combustion plant, and reduced parking to cut vehicle trips.

PM10 was the concern for the build itself dust reaching the neighbouring gardens during demolition and earthworks. That was dealt with separately through a dust management plan with phase-specific controls and real-time monitoring at the boundary.

Same site, two pollutants, two completely different solutions. Understanding which one you’re dealing with is what stops you spending money in the wrong place.

How PM2.5 and PM10 are measured

The reference method is gravimetric air is drawn through a filter for a set period, and the filter is weighed to work out the mass of particles per cubic metre. That’s the standard everything else is checked against.

In practice, most continuous monitoring uses automatic analysers that give hourly or real time readings.

Cheaper optical sensors, which measure how particles scatter light, are widely used for indicative monitoring on construction sites and indoors useful for spotting trends and triggering action, though not accurate enough on their own for regulatory reporting.

Concentrations are always reported in micrograms per cubic metre (µg/m³).

Need help with particulate matter on your project?

Whether you need baseline monitoring, a planning assessment, or a dust plan for your site, we can help. FreshBreeze Environmental provides air quality assessments, monitoring surveys and indoor air quality testing across London, Birmingham and Manchester. Call 01218272737 or email info@freshbreezeeltd.co.uk.

Conclusion

The difference between PM2.5 and PM10 comes down to size, and size decides almost everything else where the particles come from, how far they travel, how deep into the body they reach, and how UK regulations treat them.

If you’re working on a development, the practical takeaway is simple: PM10 is usually your construction phase problem, managed through dust control at the site boundary, while PM2.5 is your design stage problem, managed by cutting combustion and traffic.

Knowing which one you’re dealing with is what makes the difference between a proportionate response and wasted money.

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