When you check the weather on a sweltering summer day, you may sometimes see an air quality alert, especially if you live in a city. High levels of ozone are often to blame.

Ground level ozone, sometimes called smog, is created when certain pollutants – especially those emitted by cars, trucks, and buses – react with each other in the presence of sunlight.

Breathing ozone is harmful.

Bernstein: “The biggest problem is for people who have chronic lung illnesses like asthma and chronic obstructive pulmonary disease. But it can really affect anybody.”

That’s Aaron Bernstein of the Harvard T.H. Chan School of Public Health. He says global warming is making ozone pollution worse.

Bernstein: “We see, from data across decades now, that in cities across the world as temperatures rise, the amount of ozone that occurs at ground level goes up.”

In some cities, such as L.A., warming also causes more frequent air stagnation. That means that the air mass over the city does not move for an extended period of time, which means people have to breathe air with high levels of ozone for longer.

So, Bernstein says, burning fewer fossil fuels and slowing climate change will not only help the Earth – it will help protect people’s lungs.

Reporting credit: Sarah Kennedy/ChavoBart Digital Media.