The President was scheduled to give an Earth Day address from Cades Cove in The Great Smoky Mountains National Park. [The irony of this has been duly noted by several folk already] He would have been the second sitting US President to visit the park since its establishment in 1934. The park was named in 2002 as the most polluted national park in the country.
As fate would have it, however, Ma Nature was not in compliance with this event, and Bush was forced to give his speech from a hangar at McGhee Tyson Air National Guard Base instead. As is to be expected, Bush used this opportunity to praise his environmental record. Read more about said record here. [You'll likely notice some slight divergence between the two sources in interpretation of the aforementioned record]
South Knox Bubba has been blogging about Bush's brief visit.