21.   The company claimed this reflected its commitment to clean air, although its motives were suspect.

22.   The Environmental Protection Agency is belatedly trying to ban methyl tertiary butyl ether, or MTBE, a gasoline additive it once favored to clean the air.

23.   The leaves are said to clean the air of sulfur dioxide, found in acid rain.

24.   They come in various sizes and are usually evaluated by comparing how many times per hour they clean the air in a room of a certain size.

25.   This approach, rather than helping clean the air, underwrites and sanctifies continued industrial pollution.

26.   This is no way to treat a multibillion-dollar asset that cleans the air and enlivens the streetscape.

27.   Unocal spokesman Lane chaffed at the suggestion his company was trying to take advantage of regulations designed to help clean the air.

28.   Whatever becomes of this rule, maybe the best way to clean the air would be to reduce the idling that big rigs do.

29.   When our homes, schools or neighborhoods are exposed to elements like asbestos, we want the air cleaned until every single particle is gone.

30.   An exhaust duct was installed to draw out dust and exhaust from power machinery to clean the air inside the tunnel.