1.   The forests cannot clean the air fast enough.

2.   An ozone clean the air.

3.   Although the full-page ads say the state faces major challenges to clean the air, the umbrella theme is success.

4.   Breathing in clean winter air.

5.   But as Ms. Browner well knows, industry has long responded defensively to any suggestion that it could do more to clean the air.

6.   But proponents of stricter regulations to clean the air said studies on short-term effects indicate that those might be worse than thought.

7.   But the HEPA filters clean the air effectively, said Janczewski, removing bacteria, viruses, even pollen.

8.   But while MTBE has cleaned the air, it has polluted water, forcing the closure of wells from Maine to California, including several in Massachusetts.

9.   Cleaning the air.

10.   Doing so, he said in a memo, would demonstrate an individual commitment to clean air and reduced traffic congestion.