17. Honolulu, HI

Just in case you needed one more reason to visit Honolulu, Hawai’i—other than the breezy, cloudless 80-degree weather, the surf, and gorgeous views of the dormant volcano Diamond Head—we’ve got one: the air. You can breathe deeply in Honolulu, which again tops SustainLane’s rankings for air quality.

Located more than 2,000 ocean miles from the nearest large city, the Pacific island city’s top environment official says Honolulu should become “the model for sustainability, or risk catastrophe.” To this end, the city adopted its first sustainability plan in 2007. It’s exploring innovative waste-to-energy technologies to complement a more-than 50-percent solid waste diversion rate, and in fall 2008, residents will vote on a rapid transit line that could reduce traffic congestion and combat the city’s drive-alone rate. Honolulu could greatly increase its sustainable factor once it develops incentive programs for green building and harnesses more energy from ample sunshine and wind.

(Photo by Ron Reiring)