Voice of America: A senior United Nations Environmental official has rebuffed criticism of the air quality at the Olympic Games in Beijing saying efforts to reduce pollution have been impressive. The official also announced that Chinese basketball star Yao Ming has become a goodwill ambassador for the organization. VOA’s Scott Bobb reports from the Chinese capital. The head of the U.N. Environmental Program, Achim Steiner, Saturday said air pollution remained a concern during the Olympic Games and …