This Is Your Brain on Pollution (Update)

**Stephen Dubner** (0:04)
Hey there, it's Stephen Dubner. We recently got an email from a listener who wondered if the recent wildfires in the southeastern United States were going to affect the final exam scores for high school and college students. Not because students were displaced by the fires, but because the wildfire smoke might have affected their brains.
This listener had apparently heard an episode we made a few years ago called, This is Your Brain on Pollution. So we've decided to replay that episode for you today with updated facts and figures. As for whether this year's test scores in the southeast were affected, that sounds like an excellent research question for an enterprising investigator. If anyone out there decides to do that research, let us know.
We're at radio at freakonomics.com. As always, thanks for listening.

**Michael Greenstone** (0:58)
It's worse than cigarette smoking, it's worse than wars, it's worse than auto accidents.

**Stephen Dubner** (1:07)
Wow, what's worse than wars and car crashes and smoking?
Here, I'll give you a hint. Imagine you were getting ready to leave your house for work or school, maybe go for a run. There is some standard information that most of us seek out before leaving home. There's this.

**Andrea La Nauze** (1:24)
We've got partly sunny skies, it's 85, south winds at 14

**Stephen Dubner** (1:28)
And there's this.

**SPEAKER_1** (1:30)
We've got multiple accidents, stalled vehicles, causing major delays.

**Stephen Dubner** (1:33)
It makes sense to check the weather and traffic before leaving home, but there's information we don't usually check that could be just as important, if not more so. What if this is what you heard in the morning?

**SPEAKER_5** (1:45)
The level of particulate matter in the air today is above the recommended World Health Organization guidelines.

**Stephen Dubner** (1:51)
Or even this.

**SPEAKER_1** (1:53)
If your child has an important test today, or you're giving a big presentation at work, you might want to consider rescheduling.

**Stephen Dubner** (2:00)
Or even this.

**SPEAKER_6** (2:02)
The Supreme Court will be delaying oral arguments until next week because of a high particulate matter count in Washington, DC.

**Stephen Dubner** (2:11)
It's well established that air pollution has significant negative effects on the human body, and many places do require a public announcement when pollution levels are high. But is it possible that on a given day, high pollution can affect your brain, your cognitive abilities?

**Steve Levitt** (2:28)
So I can't say I've heard many more theories that would surprise me more if they were true.

**Stephen Dubner** (2:32)
Today on Freakonomics Radio, this is your brain.

**Angela Duckworth** (2:36)
The top card is written in black.
The bottom card is written in blue. So I'm going to say yes.

**Stephen Dubner** (2:43)
And this is your brain on pollution.

**Steve Levitt** (2:46)
It's one of the hardest things I've ever done in my life. Oh my god.

**Stephen Dubner** (2:52)
Is pollution making us more stupider?

**SPEAKER_9** (3:07)
This is Freakonomics Radio, the podcast that explores the hidden side of everything, with your host, Stephen Dubner.

**Stephen Dubner** (3:22)
Andrea Linoz is an economist at Deakin University in Australia.

**Andrea La Nauze** (3:27)
I'm an environmental economist, which means that I use data and the tools of economics to understand the causes of environmental problems and to think about policy solutions.

**Stephen Dubner** (3:38)
Air pollution is, of course, a long-standing environmental problem, chemicals like ozone and carbon monoxide, and also what's called particulate matter, or PM25.

**Andrea La Nauze** (3:49)
Tiny little particles in the air that are a diameter that is less than 2.5 micrometers. So it's more than 100 times thinner than a human hair.
And those particles can come from natural sources like dust and smoke, but also from things like the combustion of fossil fuels. So that's one of the most concerning forms of air pollution.

**Stephen Dubner** (4:11)
Particulate matter can be invisible. So unless it's really bad, you can't tell just by looking at the sky whether the air you're breathing is polluted. But the odds are that it is. The World Health Organization estimates that 99% of people around the world sometimes breathe polluted air. The WHO has different guidelines for different pollutants. For particulate matter, anything above 5 micrograms per cubic meter on average over a year is considered polluted. The average across China is 35 micrograms. The average across the US is 9
Still above the WHO threshold, but much better than it was just a few decades ago. Accordingly, our concern about pollution has been falling. In 1990, 58% of Americans said they had a great deal of concern about air pollution. Today, that number is only 40%.
Here is one of those 40%.