Finding the Right Outdoor Air Quality Monitor

In 2023, there were wildfires in Canada which blanketed the Northeastern United States with smoke. This marked a change in what parts of North America had to deal with this problem. This marked an overall increase in interest in air quality sensors.  I had looked into air quality sensors over the last few years, and there are a lot of options for indoor air quality sensors, but not quite so many for outdoor. Will talk a bit more about indoor air quality and how air quality is evaluated in a separate post.

My requirements were not achieved easily by most of the commercial options I explored. After failing to find one I liked, I built my own outdoor air quality sensor. It failed. So I rebuilt it…and it failed again…this time due to condensation somehow getting into the assembly. You can’t fully enclose the sensor because it needs air to flow over it, so there is this risk. So, after wasting two perfectly good sensors, I decided to fall back to something made by someone else as clearly I’m not that level of builder.


  • Local access to the data as opposed to having to get data from my own network from a remote API. I feed everything into Weewx, so anything with local data can be fed that way.
  • User replaceable parts
  • More than just a PM2.5 sensor.


The Other Options

That initially took me to the Purpleair line of products. Purpleair offers a several sensors plus a community of enthusiasts and their devices can be polled directly. At the time I last looked, they had what they now call the Classic…which did not her user replaceable sensors…being as the PM5003 sensors they use only have a few years of lifespan, it meant replacing the entire unit at that point. Their new Flex and Zen models allow replacement of the sensors without having to replace the whole unit, but you have to get parts from them. And the unit is are just under $300 each.

I looked at Ecowitt as well. Ecowitt sensors are sold under several names in multiple countries. They have 3 air quality sensors, only one is rated for outdoor use, and is battery operated. I tried it, but on battery it has an update time of ten minutes…which created a variety of problems in my receiver missing the update. The indoor ones allow for USB power which increases the frequency of updates.

What I Picked

I explored a few additional choices and finally found something to try. A company in Thaland called AirGradient. AirGradient is an open-source platform with a strong community behind it. They launched their first outdoor design in December of 2022.


  • They design long lasting air quality monitors that are open source and open hardware…perfect for my philosophy on the matter.
  • The prices are reasonable, and if you don’t like them, you could in theory build it yourself.
  • They provide kits to various organizations.


  • 1-3 Weeks to Ship, and 2-3 weeks once shipped to most destinations

Their outdoor unit can be purchased as a DIY kit with all the parts or as a preassembled and tested unit. It consists of:

  • Dual PMS5003T air quality sensors. The T variation includes temperature and humidity sensors.
  • Based on an ESP32 C3 chip, which means you can install Esphome…the software platform I used for my homebrew sensors
  • A sensor slot for a third sensor, they offer a TVOC/NOx board for this, an SGP40
  • While the two PMS5003T sensors are for redundancy, one could be replaced by an CO2 sensor which they sell.

The fully assembled version includes either the SGP40 or the SGP40 plus a NDIR CO2 sensor included, as well as full testing of the unit with a report.

So, I’ve ordered one of these kits for $95 with all the parts. If it works, I may order more of their products. But, even if I never order from them again, I can get PMS5003 replacement sensors from a variety of vendors and keep the one I have going indefinitely. But, if it is as advertised, I feel another weeks long order coming on.

Their indoor sensor is equally impressive, and even includes an RGB LED system to act as an air quality ‘traffic light’, but will talk about that in future.


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