Air quality - measuring PM2.5 and PM10 particulate matter
Although LimnoLog grew out of water research, the same need - to measure and understand your own surroundings - leads many people towards the air. Especially in winter, when smog settles over a town, the circle of those who want to know what they are really breathing grows: residents running community sensor networks, teachers and students, activists, researchers. Their measurements carry real weight - particulate matter is one of the most dangerous components of pollution for health.
There is the same sense of observation here as on the water: a regular reading, a fixed location, a patiently built series. And because the concentration of dust depends not only on emissions but also heavily on the weather, the measurement only takes on its full meaning when set against wind, temperature and data from official stations. It is an accessible, important and very “civic” kind of study.
What we measure
PM2.5 and PM10 are particulate matter with particles below 2.5 and 10 micrometres respectively, reported in µg/m³. The finer it is, the deeper it penetrates the respiratory system
- hence the importance of PM2.5.
How to measure it - with what and how
- Optical (laser) sensors - the backbone of citizen networks: cheap, giving a reading in real time. They require sensible placement and an awareness of their limitations (see below).
- The reference (gravimetric) method - collection on a filter and weighing; accurate, but expensive and slow. It serves as the benchmark against which sensors are compared.
Principles of a good sensor measurement:
- A location away from a direct source (chimney, exhaust pipe), at a sensible height, with free airflow.
- A fixed spot - so that the series is comparable.
- Awareness that humidity (fog, high humidity) can inflate the reading of an optical sensor - it is worth taking this into account and, if possible, calibrating against a reference station.
Read dust together with the weather and GIOŚ data
The concentration of dust is the result of emissions and atmospheric conditions: windless, frosty weather and a temperature inversion “trap” pollution close to the ground, while wind disperses it. That is why a reading takes on meaning when set against wind, temperature and humidity.
It is also worth comparing your own sensor with official GIOŚ data - Poland’s national air-quality monitoring network makes its measurements public. This lets you assess the reliability of your sensor and place a local reading within a broader picture.
Thresholds worth comparing your reading with
| Level | PM10 | PM2.5 | What it means |
|---|---|---|---|
| EU limit value | 50 µg/m³ (24 h), not to be exceeded on more than 35 days a year; 40 µg/m³ annual | 25 µg/m³ annual (stage 1); 20 µg/m³ as the stage-2 value from 2020, which several Member States apply as binding | limit values in the annual assessment of a reference station, not for a one-off reading |
| Information level | set nationally - e.g. Poland: 100 µg/m³ (24 h) | most countries set no separate PM2.5 threshold | the public is informed of the risk; advice to limit exertion outdoors |
| Alert level | set nationally - e.g. Poland: 150 µg/m³ (24 h) | most countries set no separate PM2.5 threshold | advice to limit time outdoors to the necessary minimum |
These are official thresholds for reference stations, not standards for a hobby sensor - treat the reading of an optical sensor that has not been calibrated against a reference station as an indication of the order of magnitude, not as something to compare with the table unit for unit.
⚠️ The limit values are being tightened. Directive (EU) 2024/2881, in force since 10 December 2024, replaces Directive 2008/50/EC and lowers the annual limit values from 2030 to 10 µg/m³ for PM2.5 and 20 µg/m³ for PM10. Older material still quotes 25 and 40 - check which set of values a source is using before you compare anything.
The most common mistakes
- Poor placement of the sensor (right next to a source, with no airflow).
- No reference to a reference station - an optical sensor tends to drift.
- Ignoring humidity - fog can “show” smog that is not there.
- A changing location - then the series is not comparable.
How often
Dust is usually monitored continuously (a sensor with logging), and conclusions are drawn from the series - especially during the heating season and smog episodes. A fixed location is fundamental.
Sources and further reading
National air-quality monitoring is run by GIOŚ (public data); the reference method for dust is described by European standards (including EN 12341). It is worth getting to know the information and alert thresholds for PM10.
How to make it easier
A dust measurement really “speaks” only when set against the weather and official data - and manually combining your own readings with weather and GIOŚ stations is exactly the kind of tedious work nobody enjoys.
LimnoLog takes it off your hands thanks to connectors - and shows, by the way, that it is not a “water-only” tool:
- you record PM readings (or link your sensor) as indicators in a station - including offline;
- connectors automatically pull in data from public APIs: weather from IMGW-PIB and measurements from the GIOŚ network, saving them alongside your own data, on a shared timeline;
- this lets you see dust, weather and the reference station together - inversions, windless days and smog episodes form a clear picture;
- you can share the results with the community via a public link or export them.
So the same system covers water, soil and air alike - one place for environmental measurements and their weather context.
Early users get free access for now and keep their features for good. If you measure air quality - take a look and try it.
See it in the LimnoLog app
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