Tibet, nomenclatured "the roof of the world", still seems to maintain its pristine glory. According to a regional environmental survey published in capital Lhasa, the area, free of man-made radioactive contamination and acid rain, is the least polluted in the world. Even though industrial and energy projects have been completed in various parts of Tibet in recent years, man has wreaked less havoc on the region's ecology. Using the amount of uranium, thorium, radium-226, and potassium-40 present as a reference, the survey concludes that Lhasa has the purest and freshest air on the globe.