What Do PurpleAir Sensors Measure and How Do They Work?

What PurpleAir Sensors Measure

PurpleAir sensors measure particulate matter between 0.3μm and 10μm in diameter. Additionally, they also measure the temperature, humidity, and pressure of the sensor.

Some of our newer sensors include Bosch BME680/688 sensor boards that additionally measure volatile organic compounds (VOC) emitted as gases. At this time, VOC readings are in an experimental phase. Further details about the BME680 are available in its data sheet.

It should be noted that the VOC measurements from PurpleAir devices are purely experimental. We have not seen any research or evaluations indicating that they are accurate.

PurpleAir sensors do not generally measure Ozone, but there are an extremely small number that do as the result of a project with Citizens of Clean Air.

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, real-time readings from PurpleAir devices may appear “high” when compared to 12-hour averaged data.

It should be noted that while PurpleAir sensors have been found to be highly precise in their PM2.5 and PM1 estimates, it has been demonstrated that they drastically underestimate PM10 pollution levels. As such, we do not generally recommend using them.

Learn More

Air Quality Index
PurpleAir Sensors Functional Overview
What’s the Difference Between CF1, ATM, and ALT?