According to a report conducted by China's environment ministry on air pollution, only 4 of 74 cities surveyed have acceptable levels of air pollution. The Chinese government defines the threshold for acceptable air pollution as 35 micrograms of PM2.5 per cubic meter, 10 micrograms higher than the standard set by the World Health Organization. Lhasa, Haikou, Zhoushan, and Huizhou were the only cities to meet the government's standard.