Outdoors, a CO2 monitor is going to register about 400. Indoors, you generally want it to be under 800. Above 1000 is definitely worrying. Longer explanation below the table (I’ll add an anchor link when I have more time to figure out how do that in WordPress…).
These are some readings I’ve taken. Now sorted roughly from best to worst (with caveat that my device likely isn’t the most accurate in the world, and that CO2 levels are constantly varying).
|Outdoors||Public||No||400||Measured to make sure my device was working|
|The Winery Restaurant at Peller Estates||Restaurant||No; we were the only guest (except at the very end, when two other people were seated)||407||It just stuck at this excellent reading the whole time. Large empty room, high ceiling.|
|Loloan Lobby Bar||Restaurant||No, one other couple there at first, one more couple a bit later||420||This is incredibly good ventilation for an indoor space! It stayed at this really low level the whole time. |
This space is further enhanced with filtration, in the form of Hepa filters (out where we could see them).
|Centre in the Square||Concert hall||Not very full in general (it can seat over 2000), but our area was pretty crowded.||410 to 445||This is very good. It dropped to 410 as we arrived (was higher in our car) and stayed there for about the first hour, then crept up slowly for the remaining 45 minutes of the show, but stayed at a low level. It’s an older building with a very high ceiling.|
|The Olive Board||Restaurant||Not filled but we did overlap with other patrons||420 to 450||Another eatery with excellent readings! It did bounce around a bit but never above 450, that I noticed.|
|Treadwell Cuisine||Restaurant covered patio||Definitely other people were seated on the patio, but the tables weren’t crowded together||450ish||I was just curious how it would read given that it was more outdoors-ish, and we were seated beside a heat lamp. It did bounce around, from around 420 to 470, I’d say.|
|Waterloo West Optometry||Healthcare setting||One other client in waiting area||480 (waiting room) to 630 (exam room, door closed)||Some bouncing in waiting room, but it sort of settled around 480. Couldn’t check it regularly in the exam room due to having my eyes checked, but looked at it right after leaving and it was measuring 630.|
Both are pretty good (newer building), but does show the effect of the waiting room being closer to a door regularly opening to the outside.
|Sobey’s Columbia||Grocery store||No, not on this snowy Wednesday night||500ish||Jean suggested we should move into the grocery store for better air (compared to our house).|
|Shoppers Drug Mart, Laurelwood||Pharmacy||Certainly some people there (it was a Saturday afternoon), but I wouldn’t say “crowded”.||550||Another essential store whose ventilation seems quite fine, at least under these not overly crowded conditions.|
|Dining area at The Oban Inn||Restaurant||No, one other couple besides us||550ish||This one bounced around, too, but from low 500s to low 600s.|
|Princess Twin Cinema||Movie theatre||Not overly. About 20 people there.||500 to 810||The readings bounced around quite a bit, going up, then back down. Likely whenever the air exchanger ran, it would fall, then creep up again, and repeat. The average levels did gradually increase throughout the 2.5 hour movie, though—wouldn’t fall as low as previous, then would rise higher. By the end the highs were a little above 800. I feel like it started with an average of 550 and ended more around 675 (but my device isn’t fancy enough to do any analytics).|
|My car||Private vehicle||One or two people||600 to 850+||CO2 in the car really rises when the windows are closed and the fan isn’t running.|
Once the fan gets going, it’s a noticeable improvement.
Opening windows makes the level even better.
Public equivalent: a taxi
(Not taken these measurements myself, but seen reports that trains measure around 1500, which is terrible, and buses can be even higher…)
|My house||Private residence||No (two humans, three cats)||650ish||Definitely bounces around and depends where in the house I put it, but I’d say 600, 650 is about the average. (So I’m a bit alarmed that my house doesn’t have better ventilation, actually.) |
At one point it was registering over 800. I was able to pretty quickly bring that down by opening a window. Interesting experiment.
Update: Whereas I had previously said there was no doing this, I have since found that keeping windows somewhat open most of the day does bring the house down to the low 400s, and then it will stay there for some time, even after the windows are closed again.
|The Oaklands at the Riverbend Inn||Restaurant||No; we were the only guests||700ish||One of those rooms where the CO2 levels bounced around a lot, from the mid-600s to over 800. So apparently not terribly good ventilation, as it certainly was not crowded.|
|Hair salon *||Hair salon||Three stylists, three clients, distanced||950||Jumped up above 800 shortly after I walked in and just kept going up. Not very crowded, but a fairly small space in an older building. With apparently not a great ventilation system.|
* Not going to name the specific business here, as I don’t want to give my hairdresser any grief for a situation she can’t control.
Site for reporting your own CO2 measurements, and for looking them up: https://covid-co2-tracker.herokuapp.com/home
Background on Co2 measurements
As we shift more into the “it’s everyone for themselves” phase of the pandemic, one important piece of data is how well-ventilated indoor spaces are. It’s particularly important for places where you can’t mask, like restaurants, or where it’s particularly uncomfortable to do so, like for intense gym workouts.
Covid-wise, of course, this matters more when case counts are higher, and the spaces are more crowded. But cleaner indoor is generally beneficial to your health. It’s just not something we gave much thought to before Covid.
It’s something governments need to tackle, ultimately—measuring indoor air quality, improving it in spaces they control, putting in place measures to encourage (or require) private companies to improve it as well. I plan to ask political representatives and candidates about this.
But what to do in the meantime? I’ve decided to invest in a portable CO2 monitor. And I’ve started bringing it with me to public places.
CO2 is just a proxy measurement for poor air. CO2 itself, unless incredibly high, doesn’t pose an immediate danger. But CO2 levels staying at higher levels indicate that the space isn’t very well-ventilated—it’s not doing a good job of replacing the indoor air (full of people’s COs exhalations) with cleaner air from the outdoors. (Assuming here outdoor air of generally good quality, that there’s no forest fires nearby or smog advisories.)
By the way, masking has no effect on measured CO2 levels, because it’s such a light gas, it just passes through masks. (Virus particles are larger.)
One more note: Fixing ventilation can be time-consuming and expensive in some cases. In the meantime, you can improve the situation by deploying portable HEPA units. These can (possibly) help clean virus from the air, but they do not reduce the amount of CO2. But if two spaces have high CO2, the one that has portable HEPA units or similar, like Corsi-Rosenthal boxes, is a better gamble.
Thought I might also note my experience with this, weeks 1 and 2:
- Sobey’s Columbia: 80% of staff and customers masked
- Shoppers Laurelwood: 100% of staff masked, 80% of customers
- Brady’s Deli: 0% of staff masked, 20% of customers
- Starbucks Laurelwood: 100% of staff masked, 80% of pickup customers
- Global Pet Foods, Laurelwood: 66% of staff masked (2 out of 3), 100% of customers
- Oban Inn, Niagara: 100% of staff masked
- Trius Winery, Niagara: 100% of staff masked
- Strewn Winery, Niagara: 100% of staff masked
- Peller Estates Winery Restaurant, Niagara: Staff not masked
- Oaklands at the Riverbend Inn, Niagara: Staff not masked
- Treadwell Cuisine: 100% of staff masked; vaccination proof required
- Canadian Tire: 0% of staff masked; 75% of customers
Percentages just estimates, obviously—well, except the 0% or 100% of staff, which was easy to assess.