Air quality monitoring
We have invested in a number of AirGradient ONE monitors that measure the air quality in several rooms.
Each one shows its readings on its own screen and publishes them to a public display that anyone can open.
AirGradient ONE air quality monitor
The AirGradient ONE is an indoor air quality monitor. It combines sensors for CO₂, fine particles, VOC, NOx, temperature and humidity in one box, shows the main readings on a small screen and sends them over Wi-Fi to AirGradient's dashboard. Both the firmware and the hardware are open source: the code, schematics and 3D files for the enclosure are published. All our monitors are the kit version, so they have not been calibrated or tested by AirGradient.
We chose the AirGradient ONE for several reasons:
Open source: anyone can see how it works, repair it or change it.
Transparency: AirGradient is open about its tests and claims. It publishes how its sensors are calibrated and how they compare with reference instruments, and writes plainly about what they can and cannot do.
Price: it costs less than other monitors with similar sensors.
Visible to everyone: the public displays let every member see the air quality in each room.
Model | AirGradient ONE, kit version |
Measures | CO₂, particulate matter (PM), temperature, humidity, VOC, NOx |
Licence | Open-source firmware; hardware under CC-BY-SA 4.0 |
Sensors | Senseair S8 (CO₂), Plantower PMS5003 (PM), Sensirion SGP41 (VOC, NOx), Sensirion SHT40 (temperature, humidity) |
Normal use | Switched on all the time |
Live data from the makerspace
Rooms
Room | Page |
|---|---|
3D printing room | |
Big room | |
Metal shop | |
Textile room | |
Wood shop |
Each room page has a short description and the room's live display.
What the readings mean
CO₂ (ppm): shows how well the room is ventilated. It rises with the number of people breathing in it. Outdoor air is about 420 ppm. Above 1,000 ppm the ventilation isn't keeping up; Folkhälsomyndigheten uses this level as a guide for indoor air.
PM2.5 (µg/m³): fine dust and smoke particles, small enough to reach deep into the lungs. Comes from sanding, cutting, 3D printing and soldering. The WHO guideline is 15 µg/m³ as a 24-hour average. Short peaks during dusty work are normal; the level should fall back once the work stops.
VOC (index): gases from solvents, glue, paint, resin and heated plastics. 100 is normal for the room. AirGradient describes 101–199 as a slight increase, 200–249 moderate, 250–349 significant and 350–500 severe.
NOx (index): nitrogen oxides from combustion and hot processes. 1 is normal for the room; higher means more than usual.
Temperature (°C): the air temperature where the monitor is. Machines, people and the heating all add warmth, so readings can differ between rooms and over the day.
Relative humidity (%): how much water vapour the air holds, as a percentage of the most it could hold at its current temperature. The same air shows a lower relative humidity when it warms up and a higher one when it cools. High humidity makes steel tools rust, makes wood swell and is absorbed by 3D printing filament; low humidity dries out wood and makes static electricity more likely.
How far to trust the readings
The monitors are best at showing changes and trends, such as CO₂ rising as more people fill a room and breathe out, or a spike when someone starts sanding or opens a solvent. Treat the numbers as indicators, not exact measurements.
CO₂: reliable to within a few tens of ppm. The sensor recalibrates itself by treating the lowest reading of the past week as 400 ppm, close to the level of outdoor air. This works well indoors because every room has quiet periods when no one is there and the CO₂ level drops back towards that of the incoming air.
(AirGradient blog: Why do our CO₂ sensors still calibrate to 400 ppm?)PM2.5: good at showing when dust rises and falls, less exact in absolute terms. Raw readings run high when there is a lot of dust and low in very clean air; AirGradient offers a correction for this.
(AirGradient blog: Does the EPA correction algorithm work for AirGradient monitors?)VOC: an index, not a concentration. 100 is the room's recent normal; higher means more VOCs than usual. It can't tell which gas it is or whether it is harmful (sunscreen can read as high as paint), and a long-lasting source slowly becomes the new normal.
(AirGradient blog: Explaining VOCs, TVOC and the VOC Index and TVOC – when it's useful and when it's useless)NOx: also an index. It reliably shows that a NOx event has started, but the number says little about how much, and it drops back to normal within minutes even if the source is still there.
(AirGradient blog: The SGP41 detects NOx events, but can you trust the number?)
More background on the AirGradient blog: How your AirGradient monitor handles calibration and data processing.
See Respiratory protection for protecting against dust and fumes.