BEIJING — China made remarkable progress in combating air pollution in 2020, the final year of the nation's three-year battle to bring back blue skies.

In July 2018, the country vowed to fight against air pollution in its three-year action plan, setting 2020 targets to improve major air quality indicators from their 2015 levels.

The "battle for blue skies" yielded encouraging results last year. The following are some highlights of China's achievements in this hard-fought battle.

— China has achieved the goals of its three-year action plan released in 2018, as 87 percent of all days in 2020 across 337 major cities saw good air quality readings, up 5.8 percentage points from 2015.

— Cities that failed to meet the national standards for average PM2.5 density saw their readings decline 28.8 percent between 2015 and 2020.

— China's average PM2.5 density dropped to 33 micrograms per cubic meter in 2020, down 8.3 percent year-on-year.

— The average density of PM10 and ozone (O3) fell 11.1 percent and 6.8 percent year-on-year, respectively, in 2020. It was the first time since 2015 that O3 density dropped.

— After three years of continuous efforts, the average PM2.5 density in the Beijing-Tianjin-Hebei region and surrounding areas in autumn and winter fell 32.7 percent, while the number of heavy air pollution days plunged by 62 percent from 37.4 to 14.1.

— The average density of PM2.5 in Beijing was 38 micrograms per cubic meter in 2020, a year-on-year decline of 9.5 percent and the lowest measurement since the data was first collected in 2013.