Installing air filters in classrooms has surprisingly large educational benefits (2020)

I wish there was more data on the effects of gasses in the air on people.

We seem to know:

- Elevated CO2 in rooms impairs cognitive performance.

- Elevated CO2 in submarines, at levels far higher than you would see in a normal room does not appear to impact cognitive performance.

- Installing carbon filters (what this study actually looked at) might improve classroom performance.

- People don’t like stuffy rooms.

All this is consistent with multiple hypotheses. It could be that we just don’t know anything about it. Or maybe there is some gas or gasses emitted by people that isn’t CO2 that makes people mildly uncomfortable and have worse cognitive performance.

CO2 is certainly a good proxy for ventilation quality in a space where air is exchanged with outdoors but where the gasses in the air are not otherwise changed. Carbon-filtered classrooms and submarines are not examples of this.

(Former submariner here.)

Elevated CO2 in submarines absolutely impairs performance. One example: there was a guy on my boat who got migraines when CO2 got too high - he was useless. Luckily the fix is simple - just turn on another CO2 scrubber.

There's nothing special about a submarine that makes CO2 somehow different than anywhere else.

I recall this study and maybe another one:

https://pubmed.ncbi.nlm.nih.gov/29789085/

I’m definitely not an expert.

CO2 is a proxy for many other gasses. Cheap CO2 sensors sense volatile organic compounds (VOCs), and use those to estimate CO2.

Many of those gasses do impact cognitive performance. It's not obvious to me why CO2 would, but if CO2 is going up, so is everything else we breathe out. CO2 where I am is somewhere in the ≈400ppm-1000ppm range -- 0.04% or 0.1% -- and it's pretty inert. I'm not sure what harm it does.

If it does to harm, rising CO2 levels should be much more concerning than "just" climate change.

But I suspect it's other gasses.

Rising co2 levels I believe are nowhere near the differential inside vs outside when windows are closed. There’s lots of reason to believe that rising co2 specifically lowers cognitive performance - our brains work on o2 and our body actively works to expel co2 as a waste product - increasing co2 levels means the body has less O2 available and has to work harder on co2 expulsion for survival instead of powering the brain.

What if you're low on sorbent and can't turn on another scrubber ?

I wonder if sorbent quantity correlates with performance

This is not quite correct.

1) CO2 levels have risen from under 300PPM in 1860 to over 400PPM right now -- by around 150PPM -- with a rise of about 25PPM per decade for the past four decades.

The difference in CO2 levels in my bedroom with windows open and closed is a couple hundred PPM (500-800ppm range in my bedroom, with windows open and closed, respectively). I can definitely feel a difference in performance if I don't let in fresh air. It's more than climate change (300ppm versus 150ppm range), but not big-O more, and climate change is on-track to get there in another few decades. Conference rooms might be over 1000ppm, but it still big-O similar.

2) CO2 levels are measured in parts-per-MILLION. That argument simply doesn't make sense. The atmosphere is 21% oxygen. Crowding out oxygen is simply not an issue. Critically, from personal experience, if I have some dry ice in a room, I generally don't suffer.

People run into problems when CO2 levels reach a out 5000 ppm over many hours. Even the most dense conference rooms don't hit that.

Here’s what Claude says.

1. Direct effects on brain physiology: When CO2 levels rise in the blood (hypercapnia), it causes vasodilation of cerebral blood vessels. While this initially increases blood flow, sustained elevation disrupts the brain's normal pH balance, affecting neural function.

2. Acid-base imbalance: Elevated CO2 in the blood forms carbonic acid, decreasing blood pH. This acidosis affects enzyme function, neurotransmitter activity, and neuronal excitability throughout the brain.

3. Oxygen displacement: While not typically reaching dangerous levels in standard indoor environments, higher CO2 concentrations can slightly reduce oxygen availability to brain tissues in enclosed spaces.

4. Inflammatory responses: Research suggests prolonged exposure to elevated CO2 may trigger low-grade neuroinflammatory responses, potentially impairing cognitive processes.

5. Disruption of neurotransmitter systems: CO2-induced acidosis appears to affect several neurotransmitter systems, particularly GABA and glutamate, which are critical for cognitive functions like attention, memory, and decision-making.

Studies have shown measurable cognitive effects at CO2 concentrations as low as 1,000 ppm, with more significant impairment at 2,500+ ppm - levels commonly found in poorly ventilated meeting rooms, classrooms, and offices.

As for indoor vs outdoor:

> Rising atmospheric CO2 levels from global warming don't pose the same cognitive risks as elevated indoor CO2. While indoor environments can reach 1,000-5,000+ ppm, causing measurable cognitive decline through mechanisms like acid-base imbalance and neurotransmitter disruption, global atmospheric CO2 is only about 420 ppm. Even with projected increases to 500-1,000 ppm by 2100 in worst-case scenarios, these levels remain below thresholds for significant cognitive impairment. Our bodies can also better adapt to gradual atmospheric changes compared to rapid indoor CO2 accumulation, making climate change impacts the primary concern rather than direct cognitive effects.

Crowding out O2 isn't going to be meaningful, the amount of CO2 is simply too small. If there's an effect it's from reducing the rate at which the body can expel the CO2.

If crowding out O2 was relevant why do I feel the same on our local mountain at 10,000'+ vs 0'- in Death Valley? To crowd out that much O2 with CO2 would be lethal. (That's not to say that my performance is the same. There's a big difference in the heart rate I can sustain.) What we feel is the CO2 level in our blood rising because it isn't diffusing into the lungs. Lowering O2 is only detectable with training and that's based on noting the symptoms of oxygen deficiency on brain function. (Such training is relevant in the world of aviation where it might give warning that you need to grab that oxygen mask. The average person will never encounter such conditions, nor have the resources at hand to make use of the knowledge even if they did realize it.)