@otfrom For CO2 I love my #Aranet4 monitors. Automatically discovered by #HomeAssistant, portable and I think they look neat. I paid £135/ea when they were on offer last year.
For PM2.5, I have an IKEA VINDSTYRKA. Works with zigbee2mqtt. Nothing really interesting to say tbh, it's now being used as a Zigbee repeater.
And since it's sorta related, I love the Mijia (LYWSD03MMC) Temp/Hum sensors. Current count shows I have 19 of them.
🤬 Ich hab den #aranet4 in der Waschmaschine gewaschen! 🤦 
Wir verreisen bald, deshalb waren Jacken und Taschen in der Waschmaschine, und der Sensor wohnt normalerweise fix in einer Außentasche, damit er immer mitkommt. Zu viele Taschen und Fächer, halt eine übersehen! Selber schuld.
Zu Hause brauch ich das Ding ja gar nicht. In Wien eigentlich auch kaum mehr, aber weiter weg unterwegs, da wär's jetzt einmal wirklich nützlich und interessant gewesen. 
*vorMichHinSchimpf*
For those of us still trying to avoid illness, I give high marks for the OHBM venue (Brisbane convention center): CO2 levels have stayed quite low in the auditorium, poster hall, and common areas. The symposium rooms were not as good; if more than a quarter or so full the CO2 increases rapidly. I also like that there are many easy-to-reach nice outdoor gathering places, and the opening night reception included a large patio.
None of that helps much when unmasked folks are talking loudly at close proximity, unfortunately, which happens a lot at posters, dinners, bars, etc. I'm not the only attendee masking (and no hassle about it), but we are in the distinct minority.
Mentions and black humor about covid and "colds" started at the opening ceremony and keep popping up; plenty of coughing and at least one person saying they were currently running a fever. It'd be interesting to track proportion coughing on the audio recordings over the conference and see if it actually increases or just seems to.
I haven't usually been the only person masking on trains, buses, or in shops around Brisbane, either, which is nice.
@mike_honey_ this just gave me an idea that should have been obvious. The next time I switch batteries on my #Aranet4, I'm going to put a little bit of tape on the batteries so I have a pull tab to easily extract them.
We're having a "back to office mandate" push at the moment, so the office was nearly at capacity yesterday.
Here's the CO2 readings from my #Aranet4. The two distinct spikes at the start/end of the day are the packed peak-time commuter train journeys, as they go thru the Ngauranga Gorge tunnel, and turn the ventilation to recirculation, to avoid dragging trapped diesel fumes into the carriage.
Yes; the office was worse than those trains. ALL. DAY. LONG.
At 280 canadian pesos (taxes included), the legendary #Aranet4 e-ink portable CO2 air monitor is stupidly expensive, but I'm really tempted to buy one nonetheless… for upcoming conferences/events attendance, essentially to decide when an auditorium is worth masking up in, or a room best avoided if poorly ventilated, as CO2 concentration is presumed to be a reasonably proxy measurement of air quality, and thus the risk of CoViD infection 🤔
@EmbodiedEthics This app is fantastic. Very easy to use. I don't go into indoor public spaces often, but when I do, I always try to bring my Aranet CO2 monitor and submit a reading. It's been great seeing more U.S. measurements on the map but we still need a lot more users to catch up with Germany! 😁
DrPs𝕐 
Sean Hood
dasgrueneblatt
Martin Steiger 🦋
Jo Etzel
Sheldon
Floris Bruynooghe
Phil Tanner 
Jeff Fortin T. (風の庭園のNekohayo)
ikuo