Comment by arjie
13 hours ago
What are people's target AQIs? I have indoor monitors in our high-rise building in SF and live 100 m from the freeway and we have:
PM2.5: 2.6 µg/m³
PM10: 0.5 µg/m³
VOC index: ~97
CO₂: ~505 ppm
That's the baseline. When we're cooking, like now, it's:
PM2.5: 10.8 µg/m³ (AQI ~46)
PM10: 17.5 µg/m³
VOC index: 122
CO₂: 572 ppm
None of those seem particularly concerning. We have a gas range, and 15 min past the end of cooking everything is fine. I must imagine that most people don't live right next to the freeway so they probably have even better air quality except during wildfire season.
CO2 - I'm thrilled with anything less than 800 ppm (half justified by being the lowest number I've ever seen a study suggest might have health effects, half justified by being at a point where I personally don't notice that I'm more drowsy).
PM2.5 - My impression is the health risks here are more cumulative exposure (and include things I'd like to go without in my life, like alzheimers) and a pretty straight line of "lower is better all the way to zero". The WHO's guideline is mean exposure of 5 µg/m³ so I guess I'd adopt that if I had to put a number on it. (But it's a mean, I wouldn't worry about briefly exceeding it)
PM10 - No real opinion (I'd rather worry about PM2.5)
VOC index - I'm not sure this is a standardized thing, but the version I've come across is an index relative to the average that particular sensor has seen in the last 24 hours. So there's no standard possible here.
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As for a gas range I would worry about NOX considering the studies with them causing and aggravating asthma. That said your CO2 levels are low so I suspect you might have sufficient ventilation that this isn't a huge issue for you (especially if that ventilation is in the form of a fume hood over your stove that you actually use).
CO2 by itself doesn't appear to be a problem until some truly absurd levels are somehow achieved.
CO2 is usually a proxy for air quality because outside is usually something consistent like 400 therefore deviation from that figure indicates staleness.
Careful!
https://senecaeffect.substack.com/p/the-other-side-of-co2
I don't have the list of relevant studies I've read on hand atm but there was at least one where they simply pumped in CO2 (or didn't) and had an effect showing pretty directly that CO2 itself is problematic at reasonably low levels - as well as potentially being an excellent proxy for other air quality issues. Problematic in a "makes you drowsy/stupid" type of way - not a "kills you" type of way. Though there's also at least one correlative studies suggesting it might have long term health effects (which really wouldn't be surprising if it has any short term effects).
Besides which, proxy or directly high CO2 means you should ventilate...
3 replies →
VOC index means literally nothing. (I've read the datasheet, implemented some kludges to log raw data, and contemplated the formulas. The data is high-pass filtered. You literally cannot conclude anything about a single measurement if you assume the sensor is somehow magically perfect. You might conclude that there is more VOC (or less -- not all VOCs have the same sign in their effect) when cooking than when not cooking.)
I target 0 PM2.5, but this only necessarily makes sense as a target if you have the ability to filter your home's supply air. And a good vent hood should be able to avoid any detectable bump while cooking (although a vent hood without filtered makeup air may cause a bump due to increased infiltration of exterior air).
What sensor, exactly, are you describing here? Different VOC sensors have different gas sensibilities, as well as different algorithms to interpret the gas sensor raw data.
High pass or low pass? Many instruments have a low pass filter. Very few have a high pass filter.
High pass. Probably actually band pass.
The instrument is pretty crappy - it has basically no calibration or, AIUI, long term stability. So you can’t really use it to characterize the chemical content of the air. What you can do is observe changes. I’m guessing the manufacturer wanted to avoid people getting confused by the absurd raw reasons, so they came up with a formula called “VOC Index” that HPFs the data. It will average 100 IIRC. You’re supposed to use it to notice events that cause changes - if it hits 170 every day at 2 PM them you can guess that something’s happening at 2 PM.
None of this is in the chip. It’s implemented by the driver. There’s an implementation in esphome, for example.
There's either a typo or something wrong with your sensor: you can't have pm10 < pm2.5.
(Equivalent to saying you have more people under 2.5 years old than under 10 years old.)
What? pm2.5 is smaller than pm10. You can have a bunch of larger particles that aren't small
pm10 is the mass concentration of particles with aerodynamic diameters up to approximately 10 µm, including PM2.5, so Jefftk's analogy was right. there must some kind of typo or measurement error
We have higher numbers than those and live fairly far from any freeway. Maybe your high-rise is doing better than you think.
Depending on the month, my kitchen AQI averages between 1-4, representing PM2.5 values of 0.1 - 0.8 ug/m^3. Bedrooms are likely better as they don't have the gas stove.
CO2 while occupied is generally under 750; I'd prefer to keep it under 700 but we also balance that with energy efficiency for that make-up air; I don't have an ERV, so we suffer a little there.
(We don't live by a freeway but - (a) Pittsburgh's air isn't great; and (b) the canadian wildfires were pretty bad here at times this summer, and that was what caused that 0.8 ug/m^3 pm2.5 spike).
We have, um, a lot of air filters left over from covid, though, so we're a little spoiled in terms of being able to manage AQI easily.