One surprising finding I'm having from taking CO2 readings in various places is that I'm consistently getting readings between 700 and 800 ppm at supermarkets.

I mostly took readings at peak hours. I'll need to go back at off peak times to see how much the readings change. I was really amazed at how "not terrible" the reading at Trader Joe's was.

Picture 1: Trader Joes at noon on a Saturday. It is packed. It was a total surprise to see CO2 readings between 700 and 800ppm! (Fair)

Picture 2: Smart and Final, a mostly California-bases grocery outlet selling a mix of regular groceries and bulk package items with a reading of 714ppm. (Good)

Picture 3: Walgreens Pharmacy, at off peak hours. 529ppm. This is very good, but hard to believe. I'll have to go take this again.

Picture 4: Nob Hill Foods, a small grocery chain in Northern California. 726ppm. Good-Fair.

#aranet4 #co2 #covid #traderjoe

I'm making some blunt assumptions about what these readings mean. From what I've been gathering from scientists posting about air quality readings, 400ppm is a baseline and every +200ppm gets you from excellent to good to fair to unhealthy.

Most people seem to be suggesting 800 and below as the line to really start exercising more strict caution if you're trying to avoid infection.

But keep in mind that's based on 400ppm as the baseline. My baseline for some of these readings is shown in the attached photo. It's 470ppm outdoors on that day.

My baseline is likely higher because I'm in an urban area at a mall near very busy roads. There's a lot of extra ambient CO2 so my cutoff lines would be 670 and below (excellent), 870 and below (good), 1070 and below (fair).

Every 400ppm above baseline roughly equates to 1% of the air you breathe being exhaled by someone else. That's like getting mouth to mouth once every 6-8 mins.

#aranet4 #co2 #covid

Want to see what a CO2 chart for an office meeting with about 12 people for one hour looks like? We start with excellent indoor air quality at 9am with 500ppm of CO2.

After one hour in a poorly ventilated space, the CO2 readings are 1720ppm! And this is a fairly spacious office that would have a bit of air reservoir to slow down the rise in CO2 levels.

Yikes! This means everyone is breathing quite a bit out of each other's lungs. If you're only going to wear a mask in the riskiest situations, this should be one of them.

Keep in mind that just having high CO2 concentrations doesn't mean much unless someone is contagious in the room, but if there was someone contagious that day, lots of people in that meeting would have gotten whatever was being passed into the air be it Covid, flu, RSV, or a cold.

#aranet4 #co2 #covid