Elizabeth Shogren, NPR

Tens of thousands of protesters turned out on the National Mall Sunday to encourage President Obama to make good on his commitment to act on climate change.

In his Inaugural address from outside the U.S. Capitol, the president said: "We will respond to the threat of climate change knowing that the failure to do so would betray our children and future generations."

Just a few weeks later, next to the Washington Monument, Paul Birkeland was one of a couple dozen people holding a long white tube above their heads.

Part 1 of a four-part series, Poisoned Places: Toxic Air, Neglected Communities

The system Congress set up 21 years ago to clean up toxic air pollution still leaves many communities exposed to risky concentrations of benzene, formaldehyde, mercury and many other hazardous chemicals.