Instructions
Move the map to one of the most polluted areas of the city.
Enter the construction menu with the "A" button and choose "Construction," "Environment" and "Small Park" with the directional pad and push "A" to make the selection.
Point the Wii remote to an area immediately adjacent to the polluted area and push the "A" button to build the park.
Repeat this process with as many small parks and trees as possible in the empty areas surrounding the polluted zones of the map. The pollution will quickly dissipate because the trees and parks reduce the CO2 in the area.