China will begin to implement a three-year action plan for cleaner air later this year, an environmental official said Wednesday.

The plan aims to markedly improve air quality and people's satisfaction with it, said Zhao Yingmin, vice minister of ecology and environment, at a press briefing.

By 2020, emissions of sulfur dioxide and ammonia oxides should drop at lease 15 percent from 2015 levels, while cities with low air quality standards should see their density of PM 2.5, a key indicator of air pollution, fall at least 18 percent, according to the plan.

Cities at prefecture level and above should see the number of good-air days reach 80 percent annually and the percentage of heavily polluted days decrease by 25 percent or more from 2015 levels.

To achieve the goals, authorities will optimize the industrial structure, promote clean energy, develop green transport, and strengthen regional coordination, Zhao said.

Efforts will be focused on areas including the Beijing-Tianjin-Hebei region and surroundings, the Yangtze River Delta, and the Fenhe and Weihe river plains. Economic, legal, technological, and administrative means will be adopted.

China accomplished all the major tasks of its five-year clean air action plan in 2017, but challenges remain. A large number of cities still need to further improve air quality.