Many people in cities around the world live in areas that have high levels of air pollution.
And some areas are even more polluted than others.
That can lead to serious health problems, like asthma.
And many cities have already had some major events in the last few years.
But a new study has found some cities have higher levels of risk than others, and it’s not just the air pollution that’s causing those problems.
It’s also the people living there.
NPR’s Sara Murray reports.
(This story was corrected on March 26, 2018, to say Lake City, South Dakota.)