China aims to cut the concentration of PM2.5 hazardous fine particle matter to 35 micrograms per cubic meter by 2035 from 47 micrograms per cubic meter in 2016, an official said Monday.

"It will be very difficult to reach the goal, and we need to make greater efforts to achieve it," said Minister of Environmental Protection Li Ganjie at a press conference on the sidelines of the 19th National Congress of the Communist Party of China.

PM2.5 density measures the concentration of small, breathable particles in the air and is often used as a gauge for smog.

Li praised the achievements in air pollution control since the country rolled out a major policy on air pollution in 2013.

From 2013 to 2016, the density of PM10 in the 338 cities nationwide monitored by the ministry dropped 15.5 percent, with the density of PM2.5 falling 33 percent, 31.3 percent and 31.9 percent in the Beijing-Tianjin-Hebei region, Yangtze River and Pearl River deltas, respectively, he said.

By 2020, the percentage of good air quality days must reach 80 percent across the 338 cities, the minister said.