Air Pollution Reduces IQ, a Lot

The number and quality of studies showing that air pollution has very substantial effects on health continues to increase. Patrick Collison reviews some of the most recent studies on air pollution and cognition. I’m going to post the whole thing so everything that follows is Patrick’s.


Air pollution is a very big deal. Its adverse effects on numerous health outcomes and general mortality are widely documented. However, our understanding of its cognitive costs is more recent and those costs are almost certainly still significantly under-emphasized. For example, cognitive effects are not mentioned in most EPA materials.

World Bank data indicate that 3.7 billion people, about half the world’s population, are exposed to more than 50 µg/m³ of PM2.5 on an annual basis, 5x the unit of measure for most of the findings below.

  • Substantial declines in short-term cognitive performance after short-term exposure to moderate (median 27.0 µg/m³) PM2.5 pollution: “The results from the MMSE test showed a statistically robust decline in cognitive function after exposure to both the candle burning and outdoor commuting compared to ambient indoor conditions. The similarity in the results between the two experiments suggests that PM exposure is the cause of the short-term cognitive decline observed in both.” […] “The mean average [test scores] for pre and post exposure to the candle burning were 48 ± 16 and 40 ± 17, respectively.” – Shehab & Pope 2019.
  • Chess players make more mistakes on polluted days: “We find that an increase of 10 µg/m³ raises the probability of making an error by 1.5 percentage points, and increases the magnitude of the errors by 9.4%. The impact of pollution is exacerbated by time pressure. When players approach the time control of games, an increase of 10 µg/m³, corresponding to about one standard deviation, increases the probability of making a meaningful error by 3.2 percentage points, and errors being 17.3% larger.” – Künn et al 2019.
  • A 3.26x (albeit with very wide CI) increase in Alzheimer’s incidence for each 10 µg/m³ increase in long-term PM2.5 exposure? “Short- and long-term PM2.5 exposure was associated with increased risks of stroke (short-term odds ratio 1.01 [per µg/m³ increase in PM2.5 concentrations], 95% CI 1.01-1.02; long-term 1.14, 95% CI 1.08-1.21) and mortality (short-term 1.02, 95% CI 1.01-1.04; long-term 1.15, 95% CI 1.07-1.24) of stroke. Long-term PM2.5 exposure was associated with increased risks of dementia (1.16, 95% CI 1.07-1.26), Alzheimer’s disease (3.26, 95% 0.84-12.74), ASD (1.68, 95% CI 1.20-2.34), and Parkinson’s disease (1.34, 95% CI 1.04-1.73).” – Fu et al 2019. Similar effects are seen in Bishop et al 2018: “We find that a 1 µg/m³ increase in decadal PM2.5 increases the probability of a dementia diagnosis by 1.68 percentage points.”
  • A study of 20,000 elderly women concluded that “the effect of a 10 µg/m³ increment in long-term [PM2.5 and PM10] exposure is cognitively equivalent to aging by approximately 2 years”. – Weuve et al 2013.
  • “Utilizing variations in transitory and cumulative air pollution exposures for the same individuals over time in China, we provide evidence that polluted air may impede cognitive ability as people become older, especially for less educated men. Cutting annual mean concentration of particulate matter smaller than 10 µm (PM10) in China to the Environmental Protection Agency’s standard (50 µg/m³) would move people from the median to the 63rd percentile (verbal test scores) and the 58th percentile (math test scores), respectively.” – Zhang et al 2018.
  • “Exposure to CO2 and VOCs at levels found in conventional office buildings was associated with lower cognitive scores than those associated with levels of these compounds found in a Green building.” – Allen et al 2016. The effect seems to kick in at around 1,000 ppm of CO2.

Alex again. Here’s one more. Heissel et al. (2019):

“We compare within-student achievement for students transitioning between schools near highways, where one school has had greater levels of pollution because it is downwind of a highway. Students who move from an elementary/middle school that feeds into a “downwind” middle/high school in the same zip code experience decreases in test scores, more behavioral incidents, and more absences, relative to when they transition to an upwind school”

Relatively poor countries with extensive air pollution–such as India–are not simply choosing to trade higher GDP for worse health; air pollution is so bad that countries with even moderate air pollution are getting lower GDP and worse heath.

Addendum: Patrick has added a few more.


Not buying it. Smoking is surely an order of magnitude worse than air pollution in terms of exposure to particulate matter since the emissions source is right at the lung face so to speak. In the days when most people smoked, I didn't observe that smokers were that more dumb than general population (in fact often the opposite, note Einstein was a heavy pipe smoker). Another data point, some of the most polluted cities seems to have highest IQs, like say Hong Kong and other coastal cities in China. Of course you can always tweak the data to find some correlations with whatever your preferred conclusion might be, but I think we are seeing some motivated reasoning here.

I can definitely say that back when everyone smoked, smokers didn't seem any dumber than average.

nicotine is a nootropic (, so that would confound the effect of the other things in the smoke

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Two things:

1. Modern air pollution is probably more of a chronic stressor than smoking cigarettes. I wouldn't be surprised if particulate pollution is fine if the body has enough time to deal with acute instances.

2. When you're smoking, the bulk of the pollution probably goes to your lungs, which may be better equipped to deal with pollution. Chronic pollution from normal breathing may concentrate more in your sinuses. Anecdotally, I can feel changes in my sinuses, around my eyes, and in my forehead when I encounter noticeable air pollution. The location of those effects suggests the brain is probably more directly effected.

*This comment was meant as a reply to ChrisA's comment

Lungs are not equipped to deal with pollution. The first paper claims that burning a candle indoors caused cognitive test scores to fall from 48 to 40 (out of 60). Even if the overall result is true, it’s just not plausible that burning a candle could cause a drop from 80% to 67% on a cognitive test.

TL;DR: Needs Moar Rigor.

Sample sizes of 30 and 33 people, mostly students (quelle surprise, such is life).

No mention of any attempt to isolate PM2.5 vs. other outputs (CO2, etc.), see below.

Also, am I reading their post-exposure levels chart correctly, where the SD +/- value is GREATER THAN the maximum? (Does that mean some people had zero PM2.5 exposure in the candle room, removing even the baseline environmental PM2.5? Or is it just incredibly sloppy? Or is my quick refresher of "are you sure that's what an SD value means?" somehow wrong?)

Their whisker-and-box plots of results are ... puzzling, with the strange relations of median and quartiles. This doesn't mean they're wrong, but I'd love bigger datasets and more repetition, because it sure seems odd.

The Figure 2 "levels vs. difference" plot of so weirdly random in the low bar that it undermines my confidence in their T-whatever testing, frankly; when you see people doing "20 points better" in the low concentration range I start to think "20 points of noise".

I want temperature and CO2 data to see if it was anything more than "making them sleepy".

The only confounders they mention are pre-test exposure and SES.

Which are fine, but when you're claiming to measure effects of PM2.5, you need to only expose them to PM2.5, and "heat from candles and CO2 levels" are just the obivous things I thought about while writing this.

That they couldn't think of them or weren't arsed to do anything about it makes me distrust their science as halfassed, either "because we need to publish and are lazy" or "because we got what we WANTED".

Also, another one: carbon monoxide levels.

Combine more CO2 and less O2 absorbtion from CO emissions in a closed room, with some heat, and you're ... gonna get sleepy, less sharp people, even if there was a filter that removed every speck of PM2.5.

Isolate the PM2.5 if you want to measure its effects.

(Or do CO2 and CO exposure to same levels and see if you get the SAME effect!)

After I was forced to give up smoking, I didn't see my IQ rise, alas.

Imagine what kind of airplanes Lockheed's Skunk Works could have designed in 1950-1980 if not for being cognitively damaged by all the smog in Burbank. The SR-71 would have gone 5,000 mph. The Stealth Fighter would have been the Invisible Fighter.

It would probably pay to look deeper into these figures, but the IQ of a non smoker is about 101 while that of a smoker is about 94.

We can't know that smoking is the cause of that difference though. It's also common to find more smokers below the poverty line, the same group of people that likely grew up with poor nutrition and poor education, which could contribute to a lower IQ score.

Example - - link of brain size (and the idea is executive function) to alcohol consumption.

But the correlations probably vary over time - drinking could be probably positive for brain volume in places and times where alcohol has a high cost and is a luxury good, and strong conformity pressures are present against it (so the correlations become independent thought, earning money, rather than what they might be in the West), etc.

Actually, cities in the Pearl River Delta and Fujian province have some of China’s cleanest air, due to a relative absence of heavy industry, and electricity from the three gorges dam and some local nuclear power plants. Also, there is likely a bit of a selection effect going on with Shanghai and Beijing; if you can get into a top university in those cities, you are more or less guaranteed to be able to change your hukou to that city.

I agree, seems a bit off. Given how dirty industrial cities are, it seems unlikely that if the effects are that big, no one would have noticed til now. Also, given how much time our ancestors must have spent huddled around camp fires, intuitively, it doesn't seem like homo sapiens ought to be that sensitive to a little bit of candle smoke.

In terms of polluted environments having effects which *functionally* reduce test performance, that seems plausible, through distraction and stress. Though the effects look rather large to me, if these aren't quite exaggerated stressors.

That these actually are well described as kind of "Flowers For Algernon" type effects where people are actually getting dumber rather than being obviously as intelligent but having a more distracting environment, I would question.

I would doubt that they have long term effects once you are removed from that environment, or explain much "Flynn Effect" type shifts in population performance on IQ tests (or between population persistent gaps). Tests are not conducted in heavily polluted and distracting environments, as a rule. (For the same reason they would not explain lack of high performance at the high end in some population vs another).

All the smog in Hollywood explains "My Mother the Car."

People in green houses shouldn't throw stones.

First, the last article:

Very interesting:

- the maximum distance we would expect pollutants to be blown is about 0.4 miles (~500 meters).

- Of the schools with at least one major highway within 0.4 miles, the average distance to the nearest road is 0.21miles. Fifty three percent of those schools have only one major road within 0.4 miles, 24 percent have two, 10 percent have three, and the remaining 12 percent have four or more.

22 percent of schools have 3 or more highways within 0.4 miles. The authors say car noise is not a problem. But, 3 or more highways that close, the soil may even vibrate with heavy traffic passing by.

PS. also look at school buses. Diesel engines right at the school door, not passing by.

Hi Alex, as far as I know, there's NO scientific, hence reliable, method to determine your IQ. Naturally, one is apt to ask how you knew that your IQ before and after air pollution had undergone significant change that is due to air pollution ?

Your IQ is the result you get when you take an IQ test. It's measured by taking an IQ test.

There’s NO scientific, hence reliable, method to determine your IQ.

IQ != intelligence. There's no scientific or reliable method for measuring a person's intelligence. IQ on the other hand is a human construct, so by definition the way to measure it is via an IQ test. If it varies from our experience of "how intelligent" a person is, it's not because we can't issue a good IQ test, it's because IQ is a bad proxy metric for the thing we actually want to measure.

I think IQ is meant to quantify your intelligence ; it's NOT intelligence. Nevertheless, I endorse your view that ' There's no scientific or reliable method for measuring a person's intelligence. '

What you presumably mean to say is that intelligence isn't reliably measured by IQ tests. That's a different discussion. But whatever it is that IQ tests measure, and to whatever extent *this thing* correlates to intelligence, that performance is declining as a result of air pollution.

You're NOT talking sense, I'm afraid. Without a scientific method to measure your IQ correctly, you can NEVER know your exact IQ counts. Thus, it's NOT possible for you or anybody else to know whether your IQ is rising or falling truly.

This is a really strange hill to die on.

Honestly can’t tell if you’re confusing IQ with g or this is simply part and parcel of the left wing version of the anti-science movement.

I don't think I'm confusing anything with ' g ' ( the meaning of this ' g ' is not known ). A humble seeker after the truth, my mission in life is to enlighten humanity by sharing the truth with all. Would like you to take a close look at my comments and try to grasp the points.

People in multiple threads have pointed out the flaw in your argument, yet you keep repeating the same thing. Maybe you're the one who should "take a close look at the comments and try to grasp the points."

Really sorry, sir, for being short of time to see all the comments. Would like you to refer to your points to show my fallacy. I promise you due response from me.

You're not making sense buddy. You say you're humble but then you don't even consider what the other side is saying. If you're truly humble and a seeker of truth, you have to be able to accept that possibility that you might be wrong. You don't seem humble to me at all.

What the other comments are trying to say is that IQ doesn't necessarily mean intelligence. IQ is a metric. It is a measurement that's relatively stable from test to test.

If I take an IQ test today, and then take another IQ test tomorrow, and then take an IQ test a year from now, chances are that the results will be sufficiently close to each other.

What the article is proposing is that this metric, IQ, is affected by pollution. Whether you think that IQ is a good indicator of general intelligence is up for debate.

I do accept that I'm, like any other human, NOT infallible. Your point that ' IQ doesn't necessarily mean intelligence ' sounds new and strange to me. If this view of yours is correct, I must say IQ has NOTHING to do with intelligence. Would like know what really the IQ that happens to be a ' metric ' in your view is meant to measure then. Without the right answer to this query, the IQ means something nonsensical. And my point that in the absence of the right IQ-testing method, you canNOT find the right IQ-values without which you canNOT decide whether your IQ is really changing or to what degree, it's changing.

I hear the Indian subcontinent has REALLY bad air pollution, wouldn't happen to be posting from there, would you by any chance?

I'm in India. I don't think or mean that the polluted environment improves or does NOT affect our intelligence. My point is there's NO scientific method for the quantification of intelligence ( IQ ), in the absence of which, we canNOT calculate the right value of your IQ, hence, any change in the IQ-values.


Not clear what you mean by your ' Woosh '.

There is no such thing as an IQ count, it is only the result of a test. If performance on the test falls then your IQ has fallen. Pretty straightforward?

Probably fallen. Test consistency.

Central limit theorem. No single test certain, many different tests almost certain.

Would like to know what led you to infer that ' many different tests ' no single one of which is ' certain ' are ' almost certain .'

Is this IQ that is, in your view, ' only the result of a test ' NOT meant to quantify intelligence ?

Is it the air pollution that produces lower IQs or is it the heat and humidity? Down here in the Deep South where we have lots of heat and humidity I have noticed that two digit IQs are not only common among the population generally but especially among politicians. It makes sense that two digit IQ voters would be drawn to two digit IQ politicians. Down here IQ is short for I QAnon.

I don't know why you would expect heat and humidity to confound the result. Are Northern cities like Chicago and New York unaffected while southern cities like Atlanta and Orlando are? If so it seems like that would stand out like a sore thumb.

Yes, we same the same effect up north.

Are you unaware that the implications of your theory bolster white racist ideas of superior Northern Blond Beasts?

Nietzsche's "blond beast" is the lion [literally, a lion], not a blond human.

Plainly this is pro-big-cat propaganda!

Let's bring back voter literacy tests and poll taxes. While we're at it, let's only allow people that actually pay taxes vote.

It took me a while.

Now, I get it.

It's the heat and humidity that makes me not only deplorable, but an idiot.

“ It's the heat and humidity that makes me not only deplorable, but an idiot.”

If it weren’t those two factors, the goalposts would be moved and something else would be posited.

I haven't been to India but I assume the heat and humidity there is similar to the heat and humidity down here. A favorite expression down here is that it's not the heat, it's the humidity. The combination produces all manner of dangerous byproducts, including mold (mold infections can affect cognitive function). And mosquitoes that carry disease (encephalitis anyone). And bad temperaments (bad tempered rednecks are everywhere when not at home beating their wives). We have pollution too, but it's mostly invisible: It's in the water that flows in the rivers, put there by the hundreds of chemical plants that are ubiquitous in the South. Another expression down here is that the chemical plants don't produce the products that we use, they make the products that we use better. That's nice to know.

Very interesting summary. The short term effect probably has something to do with the amount of oxygen getting to the brain? The odds ratio on Alzheimers should probably have some Bayesian adjustment, or just show the confidence interval, as it isn't statistically significant and an odds ratio greater than 3 is completely implausible here.

If I recall correctly, when controlled studies have been done on air pollution and cognitive impairment, the level of pollution used to get an effect is much larger than what is experienced outside the lab. I saw one paper presented that claimed a large effect on crime rates based on measured CO on either side of a particular Chicago highway that changed with the winds. Given that the levels of CO experienced in Chicago were I think 5-10 times less than in the lab, I didn't quite buy the results.

I wish this and the larger set of health effects (along with the horrifying geo-political effects) would receive more consideration in the public debate. We probably could justify a planned energy transformation even without climate change considerations.

Yes! Stupidest thing Greens ever did was tie eliminating petrochemicals to future climate change threat instead of making case they're killing us directly today.

That's ok. When the current lie runs it course, they can seamlessly switch to a new one.

Of course! Because, as we all know, it's a lie that burning fossil fuels produces pollution. Thanks Mr. Pants Machine!

Effects of this magnitude don't seem reasonable to me either. Especially when it comes to schools, I suspect that air pollution is just a proxy for average wealth.

Let's talk about ambiguous, incorporeal "climate change" instead.

I can't imagine how such a study could be conducted in my hometown. The elementary and middle schools are not usually adjacent to freeways, to the best of my recollection, but in any case, in what is traditionally considered the urban core, within what I guess was the first ring built back in the 50s, and which now constitutes 15% of the total land area of the city [*not* the MSA] - if you are upwind of one freeway, you are invariably downwind of another.

Things congested and close together - I thought we liked this, yes?

It seems like a more straightforward way to study the issue would be to compare the IQ or educational attainment or whatever it is you're after, within a given demographic, by nearness to the refineries along my state's coast.

But I grant I'm prolly not understanding any of this. My first infant breaths were taken just feet away from what is now a 13-lane freeway, prior to any tailpipe emission standards, but hey at least I was breathing freedom.

Later I remember taking many a sweet draft of school bus exhaust. I know we'll never convince pickup drivers to cut the engine when parked, but can we at least get the school buses to quit belching fumes while idling on perfectly beautiful days? Do we collectively have the IQ to make that happen?

If the EPA Transparency in Science rule is affirmed, then did air pollution ever really exist? Political correctness is out of control!

My assumption is that people today breath less air pollution that at any time sense the beginning of civilization, because of cooking fires.
More Nuclear and electric stoves and we can get even better.

Instrument for the role of IQ in development anyone?

"Never inhale!" - Richard Overton, died age 112. Also, "Sometimes 12 cigars a day." It's always been about the particulate matter being inhaled into the lungs. My comment here is largely directed at the examples given in other comments about the many geniuses in the past who smoked. They almost all smoked pipes, and extremely few pipe smokers inhale (though some members of other categories of smokers don't inhale as well.) The mucus system lining the nose and throat evolved to purify the air of particles before reaching the lungs. The state of mind of the people conducting the 'war on big tobacco' in the Surgeon General's reports circa 1989 was to lump all types of smoking together to not leave any potential loopholes to be used in arguments against drastic measures to reduce smoking. Just another of endless examples of the unintended consequences of noble intentions- the effects of air pollution, with the exception of the already established problems of leaded gasoline, largely drifted into research oblivion.

"Air Pollution Reduces IQ, a Lot"
So, this explains while all the city folk are low IQ Democrats and all the high IQ rural folks are Republicans?
Extrapolation is a good thing, right?

You beat me to it. +1

Seriously? Who has the bright idea that rolling back emissions laws is a good idea right now?

If you are looking for direct evidence of brain damage, there it is.

Emissions standards are a great example of bad law.

The clean fuel restrictions that CA has plus a high state level gas tax is a much better and more economically efficient method.

Seen and unseen. Raise that gasoline tax to $2.00!

"air pollution in parts of California exceeded world health standards for air quality by at least 60 times: Fine-particulate matter was clocked at 1,500 micrograms per cubic meter last year during the Camp Fire, far past the World Health Organization’s acceptable level of 25 micrograms."

Friggin California again. :)

"during the Camp Fire"

Wow. Like measuring traffic safety in Houston .. when they are 4 feet under flood water.

Rats, I should have said "Like measuring water quality in Houston .. when they are 4 feet under flood stage."


To be fair though, the severity of California’s wildfires is an explicit policy decision by the polity of California.

This equilibrium is the result of the policies the people intentionally voted in, and cheered while doing so.

Houston flooding is more akin to earthquake damage. To the point you should have made, federal flood insurance needs to be abolished to bring markets into equilibrium with the externalities.

Absolutely not.

"All of these areas support uniquely adapted groups of plants and animals, and most of these places are prone to large wildfires."

Unless you think it's "California's fault" that California is a place evolved over millions of years for hot wildfires and succession.

My opinion is that if you build a house amongst fire adapted species, understand what you are doing.

Did Los Angeles get a lot smarter when smog mostly disappeared from, say, 1980 to 2000?

L.A. used to have the world's most famous smog, so I'm surprised by how little research is done into the long term health effects of L.A.'s smog.

There should be giant amounts of school test scores, SAT scores, and the like available from Southern California to test whether the rise and fall of smog had much impact on cognition.

What are the margins? Is there good data on translating the inputs into these outputs?

How many cars driving 12K miles yearly at 30mpg (= 400 gal of gasoline), if converted to electric, would lower 10 µg/m³ in particulate matter?

Hmmm. I might need to re-think my grilling habits.

I just grilled over lump charcoal. I think I am in denial.

All that grilling has made it harder for you to think...

But no matter what, let's all agree to keep pretending we're really into boxing.
Hispanic Americans have the highest rate of urbanization, if air pollution decreased IQ and made you more violent, then why are their crime rates far below African American crime rates? Why are they very close to the more rural and surburban Whites?
In addition, China's homicide rate is 1.0 per 100000, far lower than any American ethnic group. Don't they suffer horrifically from Air Pollution?

Socrates measured his systolic and diastolic BP 30 times. Not once did the numbers come out the same. Conclusions: (1) There is no such a thing as BP, or (2) the measured BPs are shadows on the wall of the cave of BP reality. (And of course, BP constantly varies).

I mean, COME ON, at least the first study cannot be taken at face value:

Most (all but one) of the tests showed NO EVIDENCE of declining cognitive performance, while the ONE TEST that did was employed in the service of publishing the paper. The second battery of tests (before and after driving around, almost none showed significant decline, either) can be automatically dismissed not having controlled for solely exposure to air pollution.

I don't have time to check the others, but what's the point in promoting these studies here?

"Not buying it. Smoking is surely an order of magnitude worse than...."

My much older brother once told me that he attributed the success in the Space Race to two things: coffee and cigarettes.

This strikes me as pure advocacy junk science. It is all based upon PM2.5 which is a measure of particles below 2.5µ that can enter and leave the lungs. They now have economical ways of measuring these particles. but the methods say nothing about the properties.

At least ozone is a pure chemical and the same chemical everywhere. PM 2.5 is just a particle size saying nothing about what that partical is made out of. A particle of diesel exhaust (a pyrolysis product containing all sorts of nasty organic chemicals) is not the same as a salt particle from the ocean or a particle of soot covered with H2SO4 (London smog that killed people) but PM 2.5 will call them the same.

Once they developed a method to measure PM 2.5 it seems that everything is now blaimed upon PM 2.5. But how much of data really has what people are actually exposed to. I know I get a big dose on my daily walk down the surf in "Surf City". Every bubble in that foam breaks making a microdrop that drys in the air prividing that wonderful smell of beach air. I met a guy in chage of point Reis National Seashore who was in troble for the ocean air from the pacific violating PM 2.5 standards.

Without even chemical specifications on the particles and no actual mechanism for creating a measured effect, they are just "p" hacking large data sets creating psudo-scientific BS that provides "answers" desired by funders such as government agencies and activists needing to justify their actions. Give me a large medical data set and the last digits of their SS numbers and I can "prove" (using their concepts of proof) that 5% of the cancers were caused by the value of that last digit (there is a 5% probability of a false positive correlation between totally unrelated variables like cancer and SS numbers -- standard 95% confidence level of statistically significant) .

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