PurpleAir. The Pioneer in Low-Cost PM Monitors
PurpleAir played a significant role in making low-cost air quality monitors accepted by the public and government institutions. There are now a significant number of studies available comparing the PurpleAir monitors against reference instruments and proposing correction formulas to make them more accurate. It’s probably the most studied air quality monitor out there.
We at AirGradient are thankful for the impact of the PurpleAirs and the way it paved the way for other low-cost manufacturers like us.
PurpleAir Models
PurpleAir has indoor and outdoor monitors. This comparison will only focus on the two most popular outdoor monitors, the PurpleAir Classic and the PurpleAir Flex. We’ll compare these to the AirGradient Open Air models O-1PPT and O-1PST.
Accuracy
The AirGradient Open Air uses the same Plantower PMS5003 module as the PurpleAir Classic, so the monitor’s performance can be expected to be very similar.
This is confirmed by our global co-location project in which we test the accuracy of the AirGradient Open Air monitors worldwide.
Below is a chart comparing the raw data of PurpleAir and AirGradient monitors in Anacortes, USA. The PurpleAir monitor is in red, and the AirGradient is in blue. The two monitors are very well-agreed upon.
Dashboard & Map
The PurpleAir monitors can be connected to the PurpleAir dashboard and made public. Then, the monitor appears on the PurpleAir Map. The purple air map is one of the most feature-rich air quality maps and has a lot of functionality. One of the key functionalities is the ability to apply different correction formulas, e.g. to make it more accurate for wildfire smoke.
The AirGradient Map currently has fewer features but is actively being developed, and we expect to add much more functionality over the next couple of months.
PurpleAir recently stopped sharing data with OpenAQ, so historical data is no longer available on OpenAQ. Limited data can be downloaded through the PurpleAir map.
Data Ownership
PurpleAir places heavy restrictions on how you can use the data you collect with their monitor. The way the Terms are written makes it difficult to understand if your use case complies with them.
In contrast, the AirGradient Terms & Conditions do not limit your rights on data ownership or how you would like to use the AirGradient monitors.
Comparison Table by Model
The AirGradient Open Air, in its standard configuration, has one PMS5003 module and a CO2 module (model O-1PST). However, AirGradient also offers the O-1PPT model with two PM5003 modules if required.
| Criteria | PurpleAir Classic | PurpleAir Flex | AirGradient Open Air (O-1PPT) | AirGradient Open Air (O-1PST) |
|---|---|---|---|---|
| PM | 2x PMS5003 | 2x PMS6003 | 2x PMS5003T | PMS5003T |
| CO2 | None | None | None | SenseAir S8 |
| VOC | Bosch BME688 | Bosch BME688 | Sensirion SGP41 | Sensirion SGP41 |
| NOx | None | None | Sensirion SGP41 | Sensirion SGP41 |
| Temperature / Relative Humidity | Bosch BME688 | Bosch BME688 | Built into PMS5003T | Built into PMS5003T |
| Connectivity | WiFi | WiFi | WiFi (Cellular Version available) | WiFi (Cellular Version available) |
| RGB LED Light | No | Yes | No | No |
| SD Card | Yes | Yes | No | No |
| Data Ownership | Restricted | Restricted | Unrestricted | Unrestricted |
| OpenAQ Support | No | No | Yes | Yes |
| Open Source Hardware | No | No | Yes | Yes |
| Open Source Firmware | No | No | Yes | Yes |
| Price for Monitor | USD 229 | USD 289 | USD 190 (as kit USD 125) | USD 190 (as kit USD 125) |
| Price for API | Pricing | Pricing | Free for now | Free for now |
Summary
The accuracy of the PurpleAir and AirGradient monitors is similar, as they use the same Plantower PM modules. The advantages of the PurpleAir are its better map application, SD card storage, and RGB LED (Flex model). The advantages of the AirGradient Open Air are its additional sensor modules, e.g., for CO2, open source and open data license, and a significantly lower price.
Our Wishlist for PurpleAir
In case somebody from PurpleAir reads this, here is our wishlist:
- Share your data again with OpenAQ
- Give clear ownership rights to the users in your terms & conditions
- Make the PurpleAir classic easier to repair
Disclaimer
Being a monitor manufacturer makes us obviously biased when comparing the AirGradient to other monitors. However, being an open-source hardware company we are by definition a lot more transparent than traditional companies and believe we can make a relatively fair and objective comparison.
