I figured this would be interesting to share: it appears that fog – or conditions that coincide with fog – can result in increased CO₂ readings that do not reflect the real outdoor CO₂ concentration.
This is the first time I saw CO₂ measurements this high for the outdoor sensor. They don’t get this high even when I fire up a kamado in near proximity of it. Other than the fact that there was unusually dense fog that night the weather seemed regular: slight breeze, the sky cleared up after a cloudy day, the temperature cooled down (as usual,) barometric pressure measured between 993~996hPa. Interestingly, the particulate measurements from PMS5003T were measuring as usual.
(disclaimer: I’m making an educated guess that the outdoor CO₂ concentration wasn’t actually as high as reported. Although I don’t have a reference CO₂ measuring instrument at all times to compare against, I do have a CO₂ sensor that measures indoor air exhaust in my always-on ventilation system. It reading concentrations below those from outside and there wasn’t an apparent trend of those readings increasing faster than usual which is what I would expect to see if the outdoor air really had that much CO₂ in it.)