![photos](http://images.chron.com/photos/2007/03/01/6143165/311xInlineGallery.jpg)
On the Net:
Environmental Protection Agency: http://www.chron.com/disp/story.mpl/ap/nation/4777224.html
Group Against Smog and Pollution: http://www.chron.com/disp/story.mpl/ap/nation/4777224.html
Clean Air Council: http://www.chron.com/disp/story.mpl/ap/nation/4777224.html