I’m just not impressed with what you can buy right now.
I’ve been wanting some sensors to track and benchmark my indoor air quality for years – but every year when I trawl the internet there seems to be the same old stuff doing the rounds.
Cheap indoor air quality sensors?
At the low end you have the <£150 devices, which all do the same thing, but all the comments and review are terrible, or the app is bad, the data is unreliable or the data just drifts over time.
at the mid range from £150-£350 it’s slim pickings, but not much better than the cheaper ones.
At the £350-£500 range you start getting the more serious options, but these veer into the ‘hard to get data from’ or one off data sampling rather than longer term sampling over time.
So cheaper ones come with cheap and unreliable sensors which drift and ultimately give terrible results if you’re genuinely interested in the data. The data is good enough to tick the box of someone just wanting to do some spot checks, then leave it to gather dust and then ignore it forever.
Mid / higher range indoor air quality sensors
Even on some of the better £500+ devices, the software, GUI and general user experience is awful, needing a degree in something to make any sense of it.
Calibrated devices start at about £1400, but that’s out of the scope needed for benchmarking indoor air quality in reality for the ‘home’ user, so I’m gonna ignore everything in this range.
What do I actually want to track?
I want to be able to test for the following
Particulates
PM 1, PM 2.5, PM 4, PM 10, which are the main particle size that are able to be reliably tracked. PM1 is on the smaller end, with PM10 the larger end.
What do PM particle sizes mean?
| Particle type | Size | Plain-English meaning |
|---|---|---|
| PM10 | Up to 10 µm | Coarse airborne particles, such as dust, pollen, mould fragments and larger smoke particles |
| PM4 | Up to 4 µm | Close to the “respirable dust” range used in workplace monitoring |
| PM2.5 | Up to 2.5 µm | Fine particles that can travel deeper into the lungs |
| PM1 | Up to 1 µm | Very fine particles, often linked with combustion, smoke and fine indoor pollution |
| Ultrafine particles | Under 0.1 µm | Extremely small particles, often from combustion; not well measured by most low-cost PM sensors |
PM sizes and where they can reach in the body
| Particle size | Where it may deposit | Why it matters |
|---|---|---|
| PM10 | Nose, throat and larger airways | Can irritate the upper airways and contribute to visible dust or haze |
| PM4 | Deeper airways and lung regions | Useful as a rough proxy for respirable dust |
| PM2.5 | Deep lungs | A key health marker for fine-particle pollution |
| PM1 | Deep lungs; may remain airborne for longer | Useful for spotting smoke, combustion and very fine indoor particles |
| Ultrafine particles | Deep lung region; may behave differently from larger particles | Important, but usually needs specialist equipment to measure properly |
Common particle sources by size
| Source | Main PM signal |
|---|---|
| House dust | Mostly larger particles, including PM10 |
| Pollen | Mostly PM10 and larger particles |
| Mould spores / fragments | Often PM10-ish, but varies by species and conditions |
| Cooking smoke / frying | PM2.5 and PM1 |
| Wood smoke | PM2.5 and PM1 |
| Candles | PM2.5 and PM1 |
| Incense | PM2.5 and PM1 |
| Traffic pollution entering indoors | PM2.5, PM1 and ultrafine particles |
| Printers / some office equipment | Fine and ultrafine particles |
| Construction dust / sanding | PM10, PM4 and PM2.5, depending on the material and process |
| Cleaning sprays / aerosols | Fine droplets and particles; size varies widely |
PM readings: simple interpretation
| Reading | What it tells you |
|---|---|
| PM10 | Shows coarse airborne particles, dust events and larger suspended particles |
| PM4 | Useful as a rough indicator of respirable dust |
| PM2.5 | Best everyday health marker for fine-particle pollution |
| PM1 | Useful for very fine pollution, especially smoke and combustion |
| Particle counts | Can show changes in the number of particles, even when mass readings look low |
PM sizes are overlapping categories
| Reading | Means |
|---|---|
| PM10 | Particles up to 10 µm |
| PM2.5 | Particles up to 2.5 µm, which are also included within PM10 |
| PM1 | Particles up to 1 µm, which are also included within PM2.5 and PM10 |
PM readings are not separate buckets. PM1 is part of PM2.5, and PM2.5 is part of PM10.
Important note
A low-cost PM sensor is useful for spotting patterns, spikes and ventilation problems, but it does not measure every particle type equally well.
It may not fully capture:
| Limitation | Why it matters |
|---|---|
| Very large dust particles | They may settle quickly before reaching the sensor |
| Ultrafine particles | Many consumer PM sensors do not measure these properly |
| Sticky or wet particles | These may behave differently inside the sensor |
| Legal workplace dust exposure | This usually needs specialist occupational sampling |
| Particle chemistry | PM sensors measure particle size/mass, not what the particles are made from |
In short: PM sensors are excellent for seeing when airborne particle levels rise and fall, but they do not tell the whole indoor air quality story on their own.
What about Co2 tracking indoors?
There are many more things that I want to track, and one of them is Co2, specifically where I sleep – as the data shows that Co2 levels adjust how we sleep, and how well we sleep.
I have started tracking Co2 levels in my bedroom – take a look at the results here.
So… What am I gonna do about it?
Well, I’m making my own. I’m just buying the best sensors I can (within reason) and wiring them up how I want it, and create my own dashboards of data that I actually want to see – and would find useful!
Thanks,
Chris