I've been on this crusade for years now. I believe "rebreathed air" or "air straight from someone else's lungs" needs to be something we talk more about.
Here's a link to a spreadsheet that I've been sending to people recently from @DavidElfstrom:
https://docs.google.com/spreadsheets/d/1AjFzhqM_NILYvZjgE8n0CvGZzYh04JpF_DO0phrOcFw/edit#gid=0
@BE thank you! I've always wanted to better understand how that got calculated!
@RolfBly @DavidElfstrom