Wu Xiaoqing, Vice-Minister of Environmental Protection, said Friday that two-thirds of China's cities cannot meet recently updated air quality standards, adding that air pollution control will be "an arduous task for the country."

Wu's words came after the State Council, or China's cabinet, on Wednesday passed revised air quality standards that include an index for PM2.5, or fine particulate matter 2.5 microns or less in diameter. Fine particles are considered to be more hazardous to health than larger particles.

The new standards will be implemented over the course of three years and include indices for the concentration of PM2.5 and ozone (O3) over a period of eight hours. The PM10 index was previously used as part of the standards before being replaced by the PM2.5 index.