This week I’ve been on a trip down to visit my partner’s family. This is the first time I’ve flown in a while, so I decided to pick up a CO2 meter and see what the air quality was like at points along the way. CO2 is generally a good proxy metric for how fresh air is indoors. There are some caveats to this, particularly with flying, but we’ll talk about those as we get to them. The monitor I’m using is a QingPing Air Quality Monitor Lite that I got for about £65. It’s not quite as good as something like an Aranet 4, but it costs significantly less and can give a general indication. These measurements aren’t perfect but I learned something interesting and changed some assumptions that I had made before.

Starting off we begin on the tram to Edinburgh Airport. This tram was medium-busy and had a few of the little windows at the top open. The CO2 readings in here were about 1200ppm. Not great, not terrible. For reference outdoor CO2 is usually measured around 400ppm, so not the best start.

After we hopped off the tram we were straight into the airport terminal. After passing security I whipped out the air quality monitor and we got a measurement of 750ppm around all of the shops. This improved a bit as we wandered over to some quieter gates (and near and air filtering tower) where the CO2 concentration dropped down to around 490ppm, much better than the tram! I was honestly surprised how decent the air quality was around the airports I was at, and definitely made me reconsider the risk of airborne virus transmission in the quieter parts of these spaces.

The flight unfortunately was about as bad in terms of air quality as I was expecting, although it was on time for once which was a nice bonus! We were sitting around 2100ppm with the rear doors open while on the stand, which eventually dropped to around 1800ppm during the flight. This is where we should note that most airliners filter recycled air for the cabin, so using CO2 as a proxy metric while in the air isn’t really as representative as in other scenarios, like on the ground where ventilation systems are often off. Delays beware!

The next place I managed to get a reading was at an indoor table in a historical pub building (read: with poor ventilation). I was particularly interested in the readings from here because this is one of the most high-risk activities that I do — eating unmasked, indoors in a restaurant. The reading I got at my table was around 1200ppm — ouch. About the same as the tram and definitely high enough to make me a little uncomfortable. Unfortunately social obligations being what they are, it’s a risk I had to take.

Having had a lovely time in Birmingham, I began my return journey taking the train to Birmingham Airport. This service was a surprisingly busy train where I ended up standing in the vestibule as someone had taken my booked seat and didn’t want to move (a rant for another time). In the vestibule near the train doors I got a reading of 1700ppm. Oh dear. The risks of airborne virus transmissions at this level are rather high, and I’d certainly not want to be in this kinda environment without a decent mask. Thankfully I was only on this one for just under 20 minutes. The airport train was thankfully a lot lower at 740ppm and I managed to get a seat in a fairly empty carriage. I took one last quick measurement in the train station before I entered the airport and thankfully we had pretty decent air here at 860ppm, hurrah!

I arrived at Birmingham Airport ridiculously early as the security times were meant to be dreadful later on. They’re redoing the security hall, but it’s a bit chaotic while they’re doing it! As an aside, the scanners they have here are pretty handy. You don’t need to take laptops out of your bag, which makes the process of actually going through security significantly easier. The first measurement in the security hall really surprised me! I was expecting it to not be great here, particularly when Birmingham Airport’s own website says that it can get very hot in here. The queue was relatively quiet with about a 10 - 15 minute waiting time, but we had a CO2 reading of 750ppm! Honestly really reassuring as I’d previously considered airports, and in particular security halls, as some sort of air quality hell hole. This is looking good for the rest of the airport!

After an hour’s delay it was time for the final plane of the trip, which had similarly poor readings at 1500ppm, an improvement over the first flight by not by much. The readings stayed more or less like this when I checked them throughout the journey. After this final flight it was time to take the airport bus home. It was semi-busy and the CO2 started to creep up to about 1000ppm, not so great. A couple with the world’s worst cough between them got on, and I ended up moving to the back of the bus and opening up one of the windows. The CO2 didn’t drop too much while the bus was boarding with the window open, but it made a huge difference while the bus was in motion. We ended up with 400 – 500ppm for most of the journey into town.

Overall, take these readings with a pinch of salt but I’ve certainly learned a lot about where there’s good ventilation and where there’s not. Trains were definitely worse than I was expecting, airports significantly better, and flights were about what I expected. It’s definitely going to help inform what sort of transport I take in the future as a covid-cautious traveller. I’m going to be posting about the precautions I take when travelling in the coming weeks, so keep an eye out for that if you’re interested.