What PurpleAir Sensors Measure
At this time, PurpleAir sensors measure particulate matter between 0.3μm and 10μm in diameter. They also measure the temperature, humidity, and pressure of the sensor. Additionally, some of our sensors include Bosch BME680/688 sensors that measure volatile organic compounds (VOC) emitted as gases. The readings from this sensor are in an experimental phase at PurpleAir. Further details about the BME680 are available from the data sheet .
How We Measure Air Quality
PurpleAir sensors use PMS*003 series laser counters to measure particulate matter in real time (the asterisk ‘*’ represents a number determining the version of the laser counter). Each laser counter within a pair alternates five-second readings averaged over two minutes. Each laser counter uses a fan to draw a sample of air past a laser beam. The laser beam is reflected off any present particles onto a detection plate. The reflection is measured as a pulse by the detection plate. The length of this pulse determines the size of the particle. The number of pulses determines the particle count. These particle measurements are used to infer the mass concentrations of PM1.0, PM2.5, and PM10 for standard indoor and outdoor atmospheric particles. The product data manual from Plantower can provide more information.
PurpleAir sensors report real-time data that is updated every two minutes. Since air quality can fluctuate greatly throughout the day, the real-time PurpleAir AQI reading may appear “high” when compared to 12-hour averaged AQI data.