Danny Sullivan

My quest to find the best air quality monitors, both outdoors and indoors

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With wildfire smoke causing so much unhealthful air, I found myself wanting my own air quality monitors. I wanted an outdoors one both to better understand what’s happening in our immediate area and to help contribute insight to others. I wanted an indoors one to better understand what the air quality was like in our house, once we shut all the windows. After spending way to much time researching the topic, here’s what I found, in case it’s helpful to others.

Update: July 1, 2024: Much of this page has become dated, since I originally wrote it. If you’re looking for in-depth, current information, you might look at 6 best air quality monitorr we have tested from HouseFresh. That site also covers air purifiers in depth. As for my experience, after writing this post, I did get (and continue to love) a PurpleAir outdoor monitor and also have appreciated that my Dyson fans provide an indoor reading for the rare times I need that. More on both below.

Why having your own outdoor air quality monitor is useful

Let’s start with outdoors. It turns out that we have fairly sparse network of official air quality sensors because they’re expensive. This means that the air quality reported from the official sensors might be much different than your location, given it could be several miles or kilometers away. The good news is that there’s been huge growth in unofficial sensors put up by people wanting better local data. Here are some articles I found helpful about this:

PurpleAir seems to be pretty much the standard for outdoors monitoring. The PurpleAir PA-II is relatively inexpensive at $249 versus commercial products that costs thousands. It connects to wifi and feeds data into a popular map that lets you narrow in on areas and see what other owners are reporting.

Without this map (and the community sensors), I’d only have air quality information based on an official sensor about 10 miles away from me. With it, I’ve got data from three different sensors that are only about two miles away. I especially love that you can toggle off those reporting indoor air quality, which is going to generally be lower than outdoors.

Another bump for choosing PurpleAir is that its sensors are being included as an optional layer for the EPA’s AIRNow Fire & Smoke map, which is separate from (but still useful!) to the main AirNow air quality map. This is also a good article on why you’ll see different numbers from PurpleAir versus official sensors: Understanding PurpleAir vs. AirNow.gov Measurements of Smoke Pollution.

I like how PurpleAir sounded so much that I ordered one. I’m looking forward to contributing to the community map. But a gazillion other people also recently ordered one, which means PurpleAir now has 6-8 week backlog.

UPDATE (Oct. 5, 2022): Eventually I might do a review, but in short, I’ve now had PurpleAir for about two years and love it. Easy to install, and I know the outdoor air quality at my specific location. I wish they had a dedicated app rather than having to use the public map — but it works.

Alternatives to PurpleAir for outdoor air quality measurement

If you can’t get PurpleAir, or don’t want it, what other outdoor sensors might you try? Normally, I’m all about turning to Wirecutter for my buying advice, but they haven’t reviewed outdoor sensors. Fortunately, I found an amazing set of reviews conducted by California’s South Coast Air Quality Management District.

The AQMD tested many personal sensors to see how well they did against official commercial sensors. It’s an amazing resource that you’ll find here. All sensors listed were tested in the field; selected ones were brought in for lab testing. The key part of the testing summary is the R2 number you’ll see listed:

The closer that is to 1, the closer the personal sensor matched the commercial ones. You can click on any sensor listed to read the reports in more detail. From these reviews, PurpleAir got great marks. As for others:

  • IQAir AirVisual Pro from IQAir got good marks. It’s really more an indoors sensor, but the manual says it can be used outdoors in a protected area (you generally don’t want it or any of these sensors being rained on or getting wet). IQAir also has a popular crowdsourced map you can contribute to, though that really seems more powered by PurpleAir sensors. If you go to buy direct, note that the product page recently seems to come-and-go.

  • Atmotube PRO from Atmotube is a small, portable device. It’s designed to take on-the-go, so you have a sense of your air quality wherever you are. It did well enough with the AQMD test that I decided to get one in addition the PurpleAir. It’ll ship much faster, and I can use it to easily check in different rooms in my house as well as outside.

    UPDATE (Oct. 5, 2022): Atmotube turned out to be very helpful indeed for doing spot checks of rooms or if I wanted to check outside when away from my Purple Air monitors. But over the past two years, I’ve not used it much. It’s fairly rare that I’m away and wondering about outdoor air quality tht much, so I don’t generally travel with it. And my Dyson fans (mentioned below) do a pretty decent job of keeping me updated on indoor air quality.

  • Flow 2 from Plume Labs is a top portable rival to Atmotube and can also detect NO2. I liked the idea that it has a little base to power it, so that I could use it all the time more easily. But it had a very low score with the AQMD. That might change with lab testing, but it tipped me away from it.

  • AirBeam from HabitatMap looked interesting & rated OK, but I didn’t see a lot of sensors on its crowdsourced map. I prefer a device with a lot of adoption. Still, it might be a good alternative for those who can’t wait on PurpleAir, assuming they ship quickly (I don’t know if they do).

  • Air Quality Egg from (yes) Air Quality Egg rated well and has options for more than PM2.5 sensors. I love that, and I wish more of these devices would measure other types of air pollutants. But I couldn’t tell how quickly it would ship and usage according to its (slow) map seems sparse.

The links above will take you directly to the manufacturers, which do sell direct. However, if they’re out-of-stock, Amazon and other places also carry some of these sensors. Do look around.

Measuring indoor air quality

How about measuring your air quality indoors? That can be useful to tell if whatever methods you’re using to improve indoor air quality (closed windows, air purifiers) are working when it’s terrible outside.

Wirecutter has you covered here with a review of indoor sensors, plus you should probably read about suggested air purifiers or how upgrading your HVAC filter (if you have a system) might help:

Unfortunately, Wirecutter’s top indoor pick, the Kaiterra Laser Egg, is sold out right now in the US. The alternative pick, the Temtop M10, is in stock but not the wifi M10i version. I really love things having connectivity, so I passed on the alternative choice. That was made easier when I realized I already had indoor air quality sensors, those built into my Dyson fans.

I like Dyson products generally (except those awful hand dryers), and I’ve especially loved their bladeless fans for not having to be dusted. Normally, we use them in the summer when the windows are wide open, just to get some extra air moving. I’d never really thought much about the air purification part they have built in. Turns out, that’s super useful right now!

I have two Dyson fans, a DP01 and a TP02 fan. Both can sense the air constantly, even if they aren’t running. Both have wifi, which means using the Dyson app, I can see the air quality where they are. When they are running, they purify. You can also set them to “auto” so that they’ll turn on if the air quality degrades, then turn off when it improves.

Dyson didn’t make Wirecutter’s top air purifier picks, because there are less expensive and better alternatives. But those alternatives are hard to find. Dyson might be worth a look, especially with the air quality monitoring built in. Several models are in stock, both at Dyson and with various retailers. I’m also a fan of the Dyson outlet. If you don’t mind the shorter warranty, you can get a nice discount.

UPDATE (Oct. 5, 2022): I’ve continued to be very impressed with the Dyson’s having air monitoring built in. If I’m curious about a room, I can open up the app and know.