Despite strides, most U.S. kids still breathe bad air.
As Earth Week 2013 continues we take a look at the air we breathe.
While there has been some progress in reducing U.S. air pollution in recent years, as recently as 2010, two-thirds of American children lived in counties where at least some pollutants exceeded federal standards.
Pollutants such as ozone, nitrogen dioxide, sulfur dioxide and particulate matter can cause respiratory problems and exacerbate asthma in children. Asthma cases have been rising for years, with more than 10 million children diagnosed in 2010.
Authorities say children are more vulnerable to air pollution because their lungs are still developing, and they eat, drink and breathe more in proportion to their body size.