PurpleAir Flex Review: An Outdoor Sensor First, and Why That Matters
PurpleAir Flex review: two Plantower laser counters, outdoor mounting, the public PurpleAir map, AQ-SPEC field results, and which PurpleAir to use indoors.
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Specs at a glance
- Designed for
- Outdoor mounting on a wall or post (PurpleAir)
- Particle sensors
- Two Plantower PMS6003 laser counters
- Other sensor
- Bosch BME688: temperature, humidity, pressure, VOC (experimental)
- AQ-SPEC PM2.5 R²
- 0.78 to 0.88 field, 0.99 lab (PA-II-FLEX)
- Data
- Wi-Fi to the PurpleAir map; microSD logging (card not included)
- Power
- Micro USB; power supply not included
- Price
- $289 on PurpleAir's store
The PurpleAir Flex is an outdoor air quality sensor: PurpleAir designs it to mount on a wall or post outside and publish its readings to the public PurpleAir map, which many people check during wildfire season. It carries two Plantower PMS6003 laser counters, so it can compare the two and flag a failing one, and a Bosch BME688 sensor for temperature, humidity, pressure and an experimental VOC reading.
For indoor monitoring, PurpleAir itself points buyers to other models, such as the Classic Plus or the Touch. And among PurpleAir's own sensors in South Coast AQMD's AQ-SPEC field test, the Flex (PA-II-FLEX, R-squared 0.78 to 0.88) tracked reference instruments less closely than the Classic PA-II (0.93 to 0.97). Buy the Flex if you want an outdoor sensor that feeds the map; for indoors, see our indoor monitor picks.
What the Flex is for
PurpleAir sensors are best known for the community map: thousands of sensors outside homes and businesses report PM2.5 in near real time. The Flex is one of PurpleAir's outdoor units. Its readings help your neighbors as well as you, and comparing outdoor levels with an indoor monitor tells you when to close windows and run a purifier.
Sensors
| Part | What it measures |
|---|---|
| Two Plantower PMS6003 laser counters | Particle counts and mass, including PM2.5; two channels allow cross-checking |
| Bosch BME688 | Temperature, humidity, pressure, and a VOC reading PurpleAir calls experimental |
| AQI LED | A color light for the current reading |
| microSD slot | Local logging (card not included) |
PurpleAir sells replacement laser counter pairs and describes them as quick-release, which makes the Flex easier to maintain over years outdoors.
Independent test results
AQ-SPEC's summary of PM sensors lists the PA-II-FLEX at a PM2.5 R-squared of 0.78 to 0.88 in the field and 0.99 in the lab. The older PA-II Classic scored 0.93 to 0.97 in the field. Raw low-cost particle sensor readings tend to run high in humid air and smoke, which is why the US EPA developed a correction equation that it applies to PurpleAir data on the AirNow Fire and Smoke Map. When you compare a PurpleAir reading with official monitors, check whether a correction is applied.
Setup and costs
PurpleAir lists the Flex at $289 on its store, sold direct rather than on Amazon. It runs on Micro USB, and the power supply is not included; PurpleAir sells an outdoor power supply separately. It needs Wi-Fi coverage where you mount it. Mount it away from vents, grills and dryer exhausts, at a height where it gets free air but not direct rain on the intake.
Indoor use
Nothing stops you running a Flex indoors, but PurpleAir's own guidance points indoor buyers to other models, and the PurpleAir indoor PA-I scored 0.75 in AQ-SPEC's field test. For indoor monitoring with CO2 and VOCs, a purpose-built indoor monitor is the better buy; see the Qingping Air Monitor Lite or Airthings View Plus.
Who should buy the PurpleAir Flex
- Buy it if you want an outdoor particle sensor at your home that also contributes to the public map.
- Buy it if you live in a wildfire area and want hyper-local outdoor readings.
- Skip it for indoor monitoring; PurpleAir suggests other models, and indoor monitors add CO2.
- Skip it if you want the best outdoor field accuracy in PurpleAir's range; the PA-II Classic scored higher in AQ-SPEC's test.
Frequently asked questions
Is the PurpleAir Flex for indoor or outdoor use?
PurpleAir designs it for outdoor mounting on a wall or post and points indoor buyers to other models such as the Classic Plus or Touch.
How accurate is the PurpleAir Flex?
AQ-SPEC lists the PA-II-FLEX at a PM2.5 R-squared of 0.78 to 0.88 in the field and 0.99 in the lab, below PurpleAir's PA-II Classic (0.93 to 0.97) in the field.
What sensors does the PurpleAir Flex use?
Two Plantower PMS6003 laser particle counters and a Bosch BME688 for temperature, humidity, pressure and an experimental VOC reading.
Does the PurpleAir Flex include a power supply?
No. It runs on Micro USB, and PurpleAir sells an outdoor power supply separately.
Why do PurpleAir readings sometimes look high?
Low-cost particle sensors tend to read high in humid conditions and smoke. The US EPA developed a correction for PurpleAir PM2.5 data, which it applies on the AirNow Fire and Smoke Map.
Sources
- PurpleAir Flex Air Quality Monitor, PurpleAir
- Which Sensor to Choose, PurpleAir Community
- Replacement Laser Counters for PurpleAir Sensors, PurpleAir
- AQ-SPEC Sensor Evaluations: Summary of PM Sensors, South Coast Air Quality Management District
- EPA Research Improves Air Quality Information for the Public on the AirNow Fire and Smoke Map, US Environmental Protection Agency
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