In this article we will analyze all the available Technologies to Measure Particulate Matter such as PM1, PM2.5 and PM10. This article is trying to answer which type of technology is better and how they work.
First: The Laser Diffraction
Many companies use this kind of technology for their PM sensor like IQAir-AirVisual, Xiaomi, Dylos, Kaiterra-LaserEgg etc. With this technology the sensor is able to figure out the size of the particles and the quantity. This technology is also known as Optical Light Scattering because each time a particle passes and hits the laser beam then an optical sensor, like a camera’s sensor, and with the help of an algorithm will translate how many particles were in the air at that moment. This technology is very stable and the sensor can take measurements fast, typically between 3-10 seconds.
One of the problems that the laser diffraction technology has is how each pollutant is determined by the sensor. For example Black Carbon BC which is an absolute black colored pollutant will absorb some of the light from the laser beam, so it doesn’t react the same as will do a white colored particle which will reflect more light. This problem can be solved with the right algorithm but again the device won’t be able to use the right algorithm for the right pollutant unless we told it which one to use.
Second: The Infrared
The infrared technology is common in less expensive indoor AQ monitors like Foobot, Awair etc. Basic the sensor is a small chamber with two holes on opposite directions which allow the air to pass through. An infrared light is crossing the air there and an infrared sensor is able to determine the light intensiveness. Dimmer light means that pollution is passing through the holes.
One of the problems that the infrared technology has is the estimation of the particles, this technology can’t count particles, it is just guessing. There could be 1200 PM2.5 particles or 300 PM10 particles or 1 gram of sand, either way the infrared sensor will give the same measurement.
Third: The β Beta Attenuation Mass
The β Beta Attenuation Mass technology or BAM is as big and expensive as the length of its name and very uncommon to be found in an indoor environment. Governmental bodies use this kind of instrument like in UK, China etc. Basically, it samples air on a blank piece of filter paper. Then the trapped PM pollution on the paper will be bombarded with some beta radiation. Some of the PM2.5 pollutants absorb the radiation, and the differences on the other side are measured. After that, some mathematical equations are used to determine how the weakening of the β rays translates into a mass of PM2.5. Attenuation is a general term that refers to any reduction in the strength of a signal and in this case the β radiation. The BAM technology is far more accurate than the other two technologies.
There are some disadvantages with this technology too. Humidity can affect the results so proper calibration is always needed.
Some general info to have in mind that applies to all three technologies. If you have two units of the same technology side-by-side, you will still get small variations in results even between 2 BAM monitors. That’s simply because particles in air, especially PM10, aren’t necessarily uniformly dispersed.