JOHN YANG: While the United States has made great progress in recent decades, improving air quality, air pollution is still a leading cause of cancer and a driver of many other serious health problems both here and around the world.

And as William Brangham reports, air pollution appears again to be on the rise.

WILLIAM BRANGHAM: It's hard to overstate how serious air pollution is to human health.

It's responsible for nearly 7 million premature deaths every year worldwide.

In 2023, only seven countries met the World Health Organization's air quality guidelines for pollution, while more than 90 percent of countries and territories exceeded them.

Those are the findings of a new report by IQAir.

They're a Swiss research organization that also manufactures air purifiers.

The report, which gathered data from 134 countries, regions and territories, found that central and South Asia is home to the top ten most polluted cities in the world.

And here in North America, wildfires accelerated by climate change are driving even more air pollution.

Last year, that contributed to worsening air quality in cities like Minneapolis, Detroit, and Milwaukee.

Glory Dolphin Hammes is the North American CEO for IQAir, and she joins us now.

Thank you so much for being here.

I know that it's hard to generalize globally, but why are so few nations able to control their air pollution better?

GLORY DOLPHIN HAMMES, North America CEO, IQAir: It has to do with economic activity.

So the World Health Organization, their standards are essentially based on science and what actually affects human health.

And we have governments and their responsibility to provide a good economy for its constituents that actually directly conflicts with the health guidelines that are set forth.

So there is a balance between health and our economy.

WILLIAM BRANGHAM: One of the things I was really struck by in your report is that the pollution that we're talking about is incredibly small particles in the air, and that contributes to making it even more unhealthy for humans.

Can you explain why that is?

GLORY DOLPHIN HAMMES: The impact of what's called fine and ultrafine particulate matter is tremendous on the human body.

These ultra fine particles are able to penetrate the human cell mitochondria that is essentially the brain of the human cell.

And what it's able to do is to damage or kill off the cell as a result of penetrating the mitochondria.

WILLIAM BRANGHAM: So your report points out that seven nations met the WHO's guidelines for air pollution.

What is it that they're doing right?

GLORY DOLPHIN HAMMES: I believe a big function of their meeting the WHO standards has to do with geography.

They're in areas that have tremendous amount of wind.

This wind creates dilution of air pollution that's generated in terms of human activity.

That's probably, I would say, the main driving factor in meeting the WHO standards, also along with the smaller size population from these particular areas as well.

WILLIAM BRANGHAM: Your report also notes how wildfires, which we know are exacerbated by climate change, can make air quality dramatically worse.

And that seems to be one of the hardest political pollution factors to control, given that these can erupt at any time when there's dry brush in the right conditions.

GLORY DOLPHIN HAMMES: That's true.

So when we look at the 2023 report, the big X factor for Northern America is essentially the Canadian wildfires right now.

Really, there has just been a perfect storm created in terms of wildfires that we haven't really truly been able to get these wildfires under control yet.

WILLIAM BRANGHAM: A lot of people hearing this and hearing about the quality of the air around them are obviously going to be thinking, are there things that I can do for my family in my own home?

And I know you're a manufacturer of air purifying devices, but are there other things that people can do to protect themselves at a very local level?

GLORY DOLPHIN HAMMES: First and foremost, on the local level, we need to monitor air quality the same way that we monitor the weather.

That's a big change that people need to make air quality is very important because you can go days essentially without water.

You could probably go weeks without food.

But question is, how long can you really hold your breath?

And air quality is the most underestimated human need that we have.

You can do things like wear masks that actually protect the user.

And these are all important steps that people can take and they should take in order to reduce their overall exposure to air pollution.

WILLIAM BRANGHAM: All right, Gloria Dolphin Hemmes of IQAir, thank you so much for joining us.

GLORY DOLPHIN HAMMES: Thank you for having me.