A flock of sheep are seen beside Lake Namtso in southwest China's Tibet Autonomous Region, July 19, 2013. Namtso, meaning "the heavenly lake" in Tibetan language, has become one of the preferences for a growing number of tourists to Tibet. [Photo/Xinhua]

The Tibet Plateau is "the third-cleanest area in the world in terms of its environment," after the South Pole and North Pole, says a white paper issued on Tuesday, according to Xinhua.

"It has a clean and transparent atmospheric environment, and similar contents of pollutants to the North Pole," says the white paper "Development and Progress of Tibet" issued by the Information Office of the State Council.

Tibet has few types and low concentrations of pollutants, compared to other places, the white paper says, adding its atmospheric content of heavy metals is close to the background value of such elements in the global atmosphere.

In addition, the atmospheric content of heavy metals in Lhasa is much lower than that in densely populated areas and industrialized regions, it says.

The average annual mass concentration of PM2.5 -- airborne particles measuring less than 2.5 microns in diameter, is 10 micrograms per cubic meter in Tibet's non-metropolitan areas, 14.5 micrograms per cubic meter in Lhasa, and less than one-tenth of those of the areas with intensive human activities.

The white paper says the major rivers and lakes in Tibet maintain fine water quality, and the concentration of heavy metals is near the background level of global rivers and lakes ecosystem, indicating that they have not been polluted by human activities.