I've long held the belief that the best way for a thoughtful, sensible economist to have a big

impact is to tackle important problems that don't superficially seem like their economic in nature.

And my guest today, University of Chicago economist Michael Greenstone is a perfect example.

I was just blown away that the impact of air pollution seemed so large.

And if that was news to me, and I'd been studying that for 15 or 20 years, it just felt like,

well, that probably would be news to other people as well.

Welcome to people I mostly admire with Steve Levitt.

Air pollution isn't a topic you typically associate with economists, but Michael Greenstone

has spent his career investigating how it impacts human health.

Time and time again, he's found important and surprising results

and created tools that have real world impacts.

At the heart of his work is TSP's or Total Suspended Particulets.

I started a discussion by asking Michael to explain what they are

and why they cause problems in humans.

So total suspended particulates.

Already, we're going to dive into a small segment of your audience here, Steve.

When you burn fossil fuels, but especially coal and petroleum, these particles come off of them that go into the air or they're captured, but quite frequently they're not captured.

And science has gone a long ways.

It used to think that all of them were bad, and now there's kind of a narrowing into the really small ones.

And the really small ones, which are sometimes called PM2.5 or PM1, they can get deep into your body.

The bigger ones get caught, if you remember in high school biology, the cilia, those things in

your lung, the hairs, those can catch the bigger ones and then you cough them out.

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