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Comment by throwaway888abc | Hacker News Reader

400-1,000ppm Concentrations typical of occupied indoor spaces with good air exchange

1,000-2,000ppm Complaints of drowsiness and poor air.

2,000-5,000 ppm Headaches, sleepiness and stagnant, stale, stuffy air. Poor concentration, loss of attention, increased heart rate and slight nausea may also be present.

5,000 Workplace exposure limit (as 8-hour TWA) in most jurisdictions.

>40,000 ppm Exposure may lead to serious oxygen deprivation resulting in permanent brain damage, coma, even death.

https://www.kane.co.uk/knowledge-centre/what-are-safe-levels...

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> 250-400ppm Normal background concentration in outdoor ambient air

So we’d expect this site to be nearer 250 given its ideal location away from humans and industry?

The ground there sporadically goes on fire, completely naturally. So it might not be an "ideal" location for atmospheric purity.

Since it’s located on a barren volcano at a high altitude I would say there is less oxygen in the air than at sea level. The air there should also be less affected by nearby emissions.

They also have stats on the ratio of O2 to N2, which has been falling over the same period. People argue that plants will produce more oxygen to make up for the new CO2 in the air, but here we see that combustion is winning out. https://gml.noaa.gov/obop/mlo/programs/coop/scripps/o2/o2.ht...

CO2 ppm should reduce with altitude though right?

E.g. if we saw 250ppm at sea level, we’d expect to see around 3% reduction in ppm counts per 1000 ft altitude. This observatory is at 11,000ft so we’d expect 250ppm sea level to give us 82ppm not >400

No, the "parts" in ppm reduce, but the "millions" does, too. It's a ratio.

(There might be a tiny effect due to the fact that CO2 is heavier than air, so as you go up you might expect the CO2 to mostly have settled against the bottom of the atmosphere. I suspect as long as you're in the troposphere, there's sufficient mixing to make it uniform, though.)

Yeah you’re right https://www.researchgate.net/figure/In-situ-CO2-concentratio...

This is correct. CO2 is well-mixed, both laterally and vertically.

Mauna Loa observatory is at about 4200 meters, or 0.6 atmospheres. At that atmospheric height, CO2 should generally be within ~10ppm of the concentration anywhere above the atmospheric boundary layer (BL).

Below the BL, CO2 can be trapped by topography or temperature inversions, or in general, not be as well-mixed vertically. The height of the BL varies with time and location but generally that's a few hundred meters.

Well above 0.6 atmospheres -- say, 0.2 atmospheres, or > 12km up -- the CO2 concentration in ppm can decrease noticeably more.

Mauna Loa has never recorded co2 as low as 250ppm. Started at 315ppm in the 50s: https://www.noaa.gov/sites/default/files/legacy/image/2019/J...

I have a CO2 monitor, and with all the windows open the range is ~400-430. There is very little variation globally. 250 is not a reading you can find anywhere on earth anymore. CO2 diffuses very very quickly so global readings are very close to the global average.

CO2 levels vary by season, lowest in spring, highest in fall. Cause plants breath it in during sprint and exhale it out in fall (I don't remember if this is correct, or just my own misguided idea).

> CO2 levels vary by season, lowest in spring, highest in fall.

Read the article. Look at the chart. The seasonal fluctuations are much, much less significant than the rising trend.

> Cause plants breath it in during sprint and exhale it out in fall (I don't remember if this is correct, or just my own misguided idea).

Plants absorb CO2 to grow, making leaves, branches, plant material and whatnot. In the fall, leaves fall off trees, grasses die, and are metabolized by fungi and bacteria, releasing CO2.

I don't know why were speaking as though we disagree about something. I agree with everything you said.

I have my own CO2 meter inside, which I watch with some curiosity. I've observed that CO2 levels vary far more where my sensor is located, inside in an urban environment, and I was surprised to see that the CO2 levels are so steady elsewhere. [1] measured CO2 levels in an outdoor urban environments and found that sometimes the CO2 levels were about 20 times what they were at other times, 16 units vs 0.8 units. I say this as a curious observation, not as an attempt to argue against anything you said.

[1] http://www.co2science.org/subject/u/summaries/urbanco2dome.p...

Wow. That's sobering. 1,000 PPM is not far-fetched in a few decades as more poor upgrade to higher carbon lifestyles.

The growth curve so far has not been linear...

Very interesting.

I guess it’s good news it took a century of effort go from 200->420 then.

Hopefully we can stop it around 600 or so.

The concern is climate change, unlike indoor CO2 concentrations.

Yeah. These figures are completely irrelevant. The problem of increased CO2 concentration in the atmosphere isn't drowsiness, headaches and eventual suffocation, the problem is global warming. The figures seem to imply that once CO2 concentrations reach around 1000ppm we'll have a problem. But we have a huge problem right now.

I suspect it’ll be higher than that, 700 at least

The IPCC has been forecasting up to 1150 ppm by the year 2100, and they are a conservative forecaster (climate changes have been following their highest forecasts, or even higher).

So yes, your grandchildren may well live in a world where the freshest possible outdoor air is such that it makes humans feel sluggish and lethargic, like a stuffy indoor conference room today.

For covid, about < 1000ppm is a preferred ventilation rate (if humans are only co2 producer)

Mauna Loa is not indoors.

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