This is

60 Second Science.

I'm Christopher Intagiyata.

If you've gone shopping for a car lately,

you might have noticed that fuel economy,

the number of miles per gallon, is slowly creeping up.

One reason is a more efficient type of fuel injection, called Gas Direct Injection.

Its feature of half the new cars sold in the US last year.

With that kind of engine design, you can also introduce turbocharging.

That's really what it comes down to.

More engine power with a smaller engine.

Naomi Zimmerman, an air quality scientist at Carnegie Mellon University, who has, by the way, never owned a car.

Probably because I did a whole PhD on engine emissions.

Here's how the two injection methods differ. In the old

standard, called port fuel injection, gas is injected into the air intake where

it mixes with air before hitting the cylinder. In direct injection though, as the name

implies, the fuel is injected directly into the cylinder. It's more fuel efficient

meaning lower CO2 emissions, which will help slow climate change.

But here's the paradox.

It also emits more particulate matter, including black carbon or soot,

a pollutant implicated in global warming.

Zimmerman and her colleagues analyze studies of direct injection engines to see how this pollution

...