Which Sensor to Choose

PurpleAir offers different sensors that can all uniquely suit different needs. Once connected to WiFi, all of these sensors appear on the PurpleAir map, where data can be viewed and shared. With proper installation, PurpleAir sensors are weather resistant. You can view details about each sensor model below and purchase your own sensors here.


The PA-I-Indoor comes equipped with a single laser counter and a full-color LED that will glow the color associated with the current air quality (green, yellow, orange, red, purple, maroon). It is designed to sit comfortably on a counter or tabletop. This sensor is specifically meant for use indoors.


The PA-II contains two laser counters, whose numbers are compared to each other to return a self-rating Confidence Score. The PA-II does not have a full-color LED. This sensor can be used both indoors and outdoors.


The PA-II-SD is identical to the PA-II, with the addition of a microSD card and a real-time clock. While still capable of sending data to the PurpleAir map, this sensor will log its data to the internal SD card, with or without a WiFi connection. To read the data on the SD card, the SD card must be removed and plugged into a computer. This sensor could prove helpful in areas with a poor WiFi connection or serve as a backup if the WiFi connection is lost. This sensor can be used both indoors and outdoors.


The PA-II-FLEX is our latest sensor. The PA-II-FLEX has two laser counters, allowing the Confidence Score to be reported. It also includes a full-color LED that shines out of the underside of the device. This LED will glow the color associated with the current air quality (green, yellow, orange, red, purple, maroon). The PA-II-FLEX also contains a microSD card logger and a real-time clock, and the data can be viewed the same way as mentioned above for the PA-II-SD. For a limited time, a microSD card will be included. This sensor also includes a BME680 from Bosch. This component is responsible for measuring temperature, humidity, pressure, and volatile organic compounds (VOC). The VOC readings are currently experimental. The bracket on the device can be removed easily for quick maintenance on the sensor, and the laser counters are built into a quick-release system, so they are easy to access. This sensor can be used both indoors and outdoors.

The full-color LEDs display the air quality color using the US EPA PM2.5 AQI scale.

Learn More

Learn what to do to set up your new PurpleAir sensor.
Learn more about air quality and the basics of air quality monitoring.
Learn more about sensor area coverage.

It looks like the Flex contains PMS-6003 laser counters while the old PA-II devices use the PMS-5003 laser counters. Can anybody confirm that form me and also potentially dive into the nuanced differences between those two types of laser counters? If I have a bunch of both types deployed in the field, will I be able to notice a difference in readings? Will they be reasonably comparable or more like apples to oranges?


Always monitoring,

Here is a link I found that describes the difference. Curious to know if this holds up to scrutiny from others on this forum: Review: Node-S by Clarity – See The Air.

Quoting from the page: “The PMS6003 is a dual laser version of the PMS5003, for longer lifetime and has been proved to be very accurate and a better fit for particles with an aerodynamic diameter smaller than 2.5 microns (PM2.5) which makes it a perfect candidate for urban environments and vehicle emissions. Of course, it can also measure PM10 and PM1.0.”

I would like to get the Flex as well, for reasons you’ve highlighted, plus the VOC measurement. But as understood, determination of actual accuracy numbers is pending some testing Purple Air is either doing, or waiting on a 3rd part to do.


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We are told that the accuracy of the PMS6003 laser counters should be improved, especially with PM10 measurements. However, @Robert is correct that they are being evaluated, and we are waiting to hear results back.


Hi Ethan,

Did you have an ETA on those results?



Will the improvement be a firmware update or …? any updates on this?