Issue 01 - The Air Quality Index

BreatheSafeAir is an independent, one-person publication. I don't have a marketing budget or a team behind me - just a genuine interest in helping you make sense of air quality. If you find this useful, sharing it with someone who'd appreciate it means more than you'd think: {{ rp_refer_url }}

If you've been on my emailing list for a while, you'll know I haven't exactly been consistent with emails. That changes now. At least, that’s the plan!

For a while, I’ve been wanting to relaunch my newsletter and I’ve finally got around to it with The Air Quality Index. The intention is biweekly issues, and though I can't promise clockwork regularity, I will promise that when an issue lands in your inbox, it'll be worth your time.

For those of you who are new here: welcome, and thank you for subscribing. I run BreatheSafeAir, an independent one-person site where I test air quality monitors, air purifiers, and related devices. This means no paid reviews, and no manufacturer influence over what I write.

For the longer-standing subscribers - thank you for sticking around through the (quite common) radio silences. I'm grateful you're still here and your support means the world to me.

Each issue of The Air Quality Index will cover what I'm currently testing, findings that don't always make it into the full reviews, and honest takes on the devices worth your attention. If there's something specific you'd like me to cover, you can always reply to this email or let me know on the forum. I try to be as responsive as I can!

It’s good to have you here. I hope you enjoy the first issue!

The Atmotube Pro was my most used portable monitor, and I was very excited for the second generation. Part of that excitement came from rumours that it would include a CO2 sensor, meaning I could finally stop carrying a separate portable CO2 monitor alongside it. As it turned out, those rumours were true - but more on that in a moment.

As a portable PM2.5 monitor, the second generation is still excellent - the Sensirion SPS30 is one of the most validated low-cost PM sensors available, and the real-world performance is similarly good. The internal storage upgrade alone (from 256KB to 16MB, giving you up to 45 days of logged data) makes it a meaningfully better device than the original, and the addition of onboard GPS means it can now function as a proper standalone logger without needing your phone nearby.

The reason I say "so close" is the CO2 sensor. The Atmotube Pro 2 is the first device I've tested using Sensirion's new STCC4 thermal conductivity sensor, and while initial testing was promising, I've since noticed a recurring calibration issue where readings will suddenly jump by several hundred ppm and stay offset for days before correcting themselves. This appears to be related to the sensor's automatic baseline calibration. While the issue has become less frequent over the three or four months I've used the device (due to firmware updates), it hasn't gone away entirely. Until it does, I can't fully recommend it as a combined PM and CO2 monitor - which is exactly what I'd hoped it would be.

With that said, if CO2 isn't a priority for you, the Atmotube Pro 2 is still the best portable air quality monitor I've tested. I'm also still hopeful that this issue will be resolved - when it is, I'll come back to it, because I'm still very excited for the day when I can stop carrying a dedicated CO2 monitor. For more information, please read my full review at breathesafeair.com.

As I mentioned above, the Atmotube Pro 2 hasn't quite become the combined portable PM and CO2 monitor I'd hoped for (yet!). In the meantime, the AirSpot is what I carry alongside it for CO2. After over a year of almost daily use, it’s become my most-used CO2 monitor.

The size and weight are obviously the headlines, but what's kept me coming back is the app, which has been transformed over the past year into one of the most capable CO2 monitor apps available. Live activities, lock screen widgets, customisable calibration, adjustable alarms, and more. It goes further than most on the software side, and that is more important than ever when a monitor is supposed to be part of your daily routine rather than something you check occasionally.

Accuracy-wise it performs well. The SCD41 is a trusted sensor, and during my month-long comparison I carried the AirSpot alongside both the Atmotube Pro 2 and a factory-calibrated Aranet4 Home because I was curious to see how the photoacoustic SCD41 would fare against the STCC4 and a traditional NDIR sensor at the same time. The AirSpot tracked very closely with the Aranet4 Home throughout.

There are occasional sound/vibration-related spikes, but these are manageable. Really, the only thing still missing with the AirSpot monitor is temperature and humidity graphing in the app. The sensor measures both, but they're not surfaced yet. Either way, if portability is your priority for CO2 monitoring, nothing else comes close. My full review can be found here.

A few of you have asked about the IKEA Alpstuga, and I understand why. It's remarkably affordable for what it is, and it uses Sensirion's new SEN63C platform - which, if I'm right, uses the same thermal conductivity CO2 technology as the STCC4 in the Atmotube Pro 2. That makes it very interesting from a technical standpoint, and that’s before you even get to the price!

The problem is availability. They're not sold locally here, and every time I've tried purchasing one through a forwarding service, the nearest IKEA stores have been out of stock. I'm happy to wait until one turns up, but if you happen to have easy access to one and are willing to ship it my way, I'd really appreciate it and will cover the cost. Feel free to reply to this email if you think this could be possible!

That's it for this first issue of The Air Quality Index. If you have a device you'd like me to review, or a topic you'd like me to cover in a future issue, just reply to this email - I read every response and always take requests into account when planning future reviews.

If you found this useful, the best thing you can do is forward it to someone who'd appreciate it. It costs nothing and it means a lot to an independent, one-person publication like this one.

See you in a couple of weeks.

Ethan