Our Technology

General
1

Based on a new generation of low-cost laser particle detectors, PurpleAir sensors use WiFi to communicate and upload data to the cloud from where it is shared on the PurpleAir map.

Sensor Hardware

Laser Particle Counter:

PurpleAir uses PMS6003, PMS5003, and PMS1003 laser particle counters. These sensors count suspended particles in sizes of 0.3, 0.5, 1.0, 2.5, 5.0, and 10um. These particle counts are processed by the sensor using a complex algorithm to calculate the PM1.0, PM2.5, and PM10 mass concentration in µg/m³. PMS sensors come factory calibrated.

Before deploying any devices, we verify that they are giving out readings that are consistent from sensor to sensor during tests in a smoke chamber.

ESP8266 and Arduino air quality sensor:

PurpleAir sensors use an ESP8266 chip to talk to the particle counter and provide all functionality, including connecting to a WiFi network and uploading data to the cloud. PurpleAir firmware has remote update features, meaning we can modify the software and the sensor will download the new version and update itself. Each PurpleAir air quality sensor device checks for updates from time to time.

Bosch Environmental Sensor:

Each PurpleAir sensor includes a Bosch pressure, temperature, and humidity sensor. Most of our older sensors, including the PurpleAir Classic, use the BME280. Our newer models (Touch, Flex, and Zen) now incorporate a BME680 or BME688, which include a gas sensor.

Please note: Temperature and humidity values may differ from ambient conditions due to heat generated by the WiFi module, sun, and other possible influences. These values are provided as-is and are meant to give an indication of the operating conditions for the PurpleAir device. Generalized correction factors are applied to temperature and humidity data presented on the map, but this correction will not cover all circumstances.

Power Supply:

PurpleAir sensors are powered by a 5v USB power source. Read about the power supply that PurpleAir offers here.

Software

Google:

Using services from Google makes for a robust, reliable, and secure system. Google App Engine provides the hosting for the PurpleAir map.

PurpleAir also uses BigQuery by Google for data storage and the PurpleAir API.

HighCharts:

PurpleAir uses HighCharts and data stored by Google’s BigQuery to create graphs on the PurpleAir map.

Mapbox:

Mapbox provides the geographic map data for the PurpleAir Map.

2 Likes
2

“Our FLEX sensor now also incorporates BME680 or BME688 which include a gas sensor.”

That Bosch sensor(s) is configurable. Which gasses has Purple Air configured it to detect?

1 Like
3

Hello skome,

We have not configured them yet. That is something we plan on doing in the future, but do not have a timeline currently.

1 Like
4

At the moment, the only output from the BME680/BME688 (beyond humidity, temp, and pressure) is the Static IAQ.

1 Like
5

My understanding is that it uses a MOX sensor, which detects a variety of gases in summation only. It cannot selectively be configured to detect only certain gases. See section 3.3 here: https://www.bosch-sensortec.com/media/boschsensortec/downloads/datasheets/bst-bme688-ds000.pdf

2 Likes
6

However, it appears that they are trying to do some “fingerprinting” with the electrical resistance values of different chemicals. I’m not sure how practically feasible this is in ambient settings (e.g. outdoors. ie. not a sealed container of coffee beans). https://www.bosch-sensortec.com/media/boschsensortec/downloads/application_notes_1/bst-bme688-an001.pdf

2 Likes
8

These (independent, non-government air monitoring efforts) are currently being attacked by Indonesian (Jakarta local) government - by claiming that “those devices are not certified”

Can you describe what kind of certifications these device / parts already acquired?

I’ve looked around, but couldn’t find any info about it.

Thank you.

2 Likes
9

Would you please tell me which one is better in terms of RH and temperature measurement than the classic model? And see how the Zen model compares

1 Like
10

Hello Harry, thank you for reaching out! I’ll share a couple of points that I hope will prove helpful:

1. PurpleAir sensors serve a different purpose than government monitors

Government monitors are expensive to purchase and more expensive to run/maintain. It is cost-prohibitive to place them in every neighborhood, and they cannot monitor the air as frequently as PurpleAir sensors can. Therefore, they’re best used to understand air quality more widely, and they are usually not placed near pollution sources.

PurpleAir sensors, on the other hand, are much cheaper to set up a dense network with. They only need power and internet to monitor and upload their data. This makes them a great solution for understanding air quality where people live––on every street corner and such. The high-frequency data uploads enable citizens to make decisions about outdoor activities right now, rather than once an hour or once per day.

2. PurpleAir sensors have been evaluated extensively by air quality researchers and regulators all over the world

PurpleAir sensors have been found to be highly precise and to correlate well with federal reference methods. A number of formulas have been made to calibrate PurpleAir data for PM pollution monitoring in various regions and climates.

Here are a couple of examples of governments using PurpleAir data:

  • The AirNow Fire and Smoke Map is a collaborative effort between the US Environmental Protection Agency (US EPA) and the US Forest Service (USFS) that displays PurpleAir sensors alongside government monitors.
  • The Canadian AQ Map is a collaborative effort between Environment and Climate Change Canada (ECCC) and the University of Northern British Columbia (UNBC) that does something very similar with PurpleAir sensors and government monitors in Canada.

I hope this helps make the value and use case for PurpleAir sensors more clear. Please let us know if you have any questions.