Particulate matters(PM) refer to the liquid or solid matter suspended in the air. PM2.5 refers to the particles of size 2.5 micrometers or smaller. These coarse particles enter the body and can be found even inside our lungs. Finer particles even enter our bloodstream as well. A PM2.5 sensor uses the scattering of light to find the concentration of PM2.5 in the given air sample. PM2.5 is a good pointer of air quality, hence PM2.5 sensor is used to monitor the air quality.
How does it work?
A PM2.5 particulate sensor usually packs a laser module, a fan to control the airflow, a photodiode, and a microprocessor. The fan and processor are on constant feedback to control airflow. The laser beam illuminates the particles in the air, inside the sensor. These particles scatter the light, and the photodiode detects the variation in light falling on it. The light-dependent diode generates a voltage based on the incident light. The voltage readings from the photodiode are then fed to the microprocessor. The microprocessor is programmed to convert this voltage data into mass/number concentration of the particulate matter.
Calibration of the sensor
A PM2.5 particulate sensor has to be calibrated before testing. Most cheap sensors assume that all the particles are similar. But in reality, the air has particles with different weights and different refractive indexes as well. The above assumption can cause an error in the readings. Hence, it is not advised to use the cheap PM2.5 sensors for researches. But, modern PM2.5 sensors are capable of avoiding this error factor to measure the particulate matter concentration precisely.
PM concentration value is an indicator of air quality. The lesser the concentration, the better the quality. PM2.5 sensors are used world-wide to track air quality. Yet, their range is very small and not suitable for finding the air quality of a larger area. Many public institutions have set up PM2.5 sensors and they share this data online. They are accessible to anyone who wants to find it.
PM2.5 sensors are also used in monitoring emissions. They are used to test the emissions from a combustion system. This way, we can understand how the system is working in terms of efficiency. PM2.5 sensors are rather cheap and can be installed easily. Understand your requirement before you choose a PM2.5 sensor.