How are you this week, and how is your breathing? It is a question few of us ask, yet we take around 20,000 breaths every day. As the clocks go back, bonfire season starts and the heating comes on, it is worth knowing what is in that air.
This guide answers one question in plain English: what is PM2.5? We start with particulate matter and its main types, then focus on PM2.5. PM10 and PM1 get their own Friday Nuggets in the coming weeks.
What is particulate matter?
Particulate matter (PM) is a mix of tiny solid and liquid particles suspended in the air. Some come from nature, such as pollen, sea salt and wind-blown dust. Many come from human activity: traffic, burning, construction and industry.
Scientists group particles by size, measured in microns (one micron is a thousandth of a millimetre). The smaller the particle, the deeper it can travel into the body.
Types of particulate matter
| Type | Size | How far it can reach |
|---|---|---|
| PM10 | 10 microns or smaller | Nose, throat and upper airways |
| PM2.5 | 2.5 microns or smaller | Deep into the lungs, possibly the bloodstream |
| PM1 | 1 micron or smaller | Deeper still |
| Ultrafine particles | Smaller than 0.1 microns | The smallest and least understood |
What is PM2.5?
PM2.5 is particulate matter 2.5 microns or smaller in diameter. That is roughly 30 times thinner than a human hair. You cannot see individual particles, but on hazy days you see them together as smog.
Where does PM2.5 come from?
- Wood burning stoves, bonfires and fireworks
- Brake, tyre and road wear, plus vehicle exhaust
- Construction and demolition dust
- Industry and agriculture, including ammonia from farming that forms secondary particles
- Pollution carried in from other regions and countries
Why does PM2.5 matter for your wellbeing?
Because it is so small, PM2.5 can travel deep into the lungs and may pass into the bloodstream. Long-term exposure is linked to heart and lung disease, stroke and other serious health effects. Children, older people and people with existing heart or lung conditions are more vulnerable.
What are the PM2.5 limits in the UK?
| Standard | Annual mean PM2.5 | Deadline |
|---|---|---|
| WHO Air Quality Guideline (2021) | 5 µg/m³ | Health-based guideline |
| England interim target | 10 µg/m³ | December 2030 |
| England legal target | 10 µg/m³ | 31 December 2040 |
| England population exposure target | 35% lower than 2018 | 31 December 2040 |
The 2040 targets are set in the Environmental Targets (Fine Particulate Matter) (England) Regulations 2023. The 2030 interim targets are in Defra’s Air quality Environment Act target delivery plan.
Three quick wins for cleaner air
- Check local air quality on UK-AIR before outdoor exercise.
- Burn only “Ready to Burn” certified fuel, or skip burning altogether.
- On site, damp down, cover stockpiles and switch off idling engines.
Why should developers, architects and contractors care?
PM2.5 is increasingly considered in planning applications, air quality assessments and construction dust management plans. Thinking about it at the design stage can help avoid delays and planning conditions later. Read more about our air quality assessments and air quality and dust management plans.
PM2.5 FAQs
Is PM2.5 worse than PM10?
PM2.5 particles are smaller, so they can travel deeper into the body. PM10 includes PM2.5, so the two are measured and managed together.
Can I see PM2.5?
Not individually. You may see it together as haze or smog on high-pollution days.
Is indoor air free of PM2.5?
No. Outdoor PM2.5 enters buildings, and indoor sources such as wood burners and cooking add to it. Find out more about indoor air quality assessments.
Does PM2.5 affect planning applications?
It can. Local authorities may ask for an air quality assessment for planning covering PM2.5, especially for larger schemes or sites near busy roads.
Conclusion: the key takeaways
PM2.5 is fine particulate matter you cannot see but breathe every day. It comes mainly from burning, traffic, construction and industry. England’s legal target is 10 µg/m³ by 2040, while the WHO guideline is 5 µg/m³. Small daily choices, and good planning on site, both help.
Have a question about PM2.5 or an upcoming project? Contact Freshbreeze Environmental, call 0121 827 2737 or email info@freshbreezeeltd.co.uk. Next Friday: PM10 explained.
Need this for your site? Freshbreeze Environmental provides air quality monitoring and NO2 diffusion tube surveys across the UK. Send us your site details for a quote or call 0121 827 2737, and we will reply within 24 hours. Related guide: PM2.5 vs PM10, the key differences
