Michael Greenstone

And the reason they don't exist in the United States anymore is largely due to the cleaner air.

The Central Valley in California remains pretty polluted.

There's parts of the Midwest that remain pretty polluted.

But relative to the WHO standard, the United States is very clean.

The majority of the problem is concentrated in Asia, especially in India, Bangladesh, China, and in some parts of sub-Saharan Africa.

We have probably been understating the losses from air pollution by about 50%.

You know, it's a very well done paper in a kind of artificial setting.

Long run meaning is a little bit hard to suss out.

The more challenging thing is, you know, to find instances where there's long run variation.

I think in both the health and in the cognition literatures,

The holy grail is not to rely on studies that use either day to day or month to month, but to find a setting where there's like a permanent difference in air pollution.

It's much harder to come up with those examples, but that is after all what policy is trying to do.

It's not trying to reduce pollution on Tuesday.

It's trying to reduce pollution 365 days a year.

Greenstone thinks he may have found the Holy Grail.

About seven or eight years ago, I stumbled upon an example from China that seemed to mimic this kind of ideal.

And that's something called the Huai River Winter Heating Policy.

It dates back to when China was much less wealthy, and there just weren't enough resources to provide winter heating for everybody.

So they did something quite arbitrary and capricious.

They drew a line across the middle of the country, and that line follows the Huai River.