One way the city could really spear-head all of the pollution that's floating around their air intake is to fund the planting of MORE TREES. The metro area is actually heavily wooded, but, they have a problem with not using the mass transit they have available in the outlying areas like Alpharetta, Roswell, and Gwinett. That is, from what I've seen.
But, the major thing that the cities in North Alabama have done, though not Decatur, Grrrr, is plant Ginkgoe trees. Cities like Florence, Huntsville, even some in Madison have planted these and I've been able to notice a difference. I've seen quite a few in downtown Montgomery too. Anyways, they love the carbon dioxide and are one of the best trees to filter out greenhouse gases. That's why the highways in DC are nasty but the parks are beautiful, cause they have those HUGE Ginkgoes growing around the place.
Decatur, Alabama: 54,528
Morgan County, AL: 115,237
Decatur Metro Area: 149,549
Huntsville-Decautr CSA: 526,302