LANZHOU -- Lanzhou, the capital city of northwest China's Gansu province, recorded an air quality composite index of 4.75 in 2021, the best since the implementation of new evaluation criteria in 2013.

The air quality composite index is a comprehensive analysis of six pollutants; the higher the number, the more serious the pollution.

Lanzhou's air quality has been improving, with the index decreasing from 6.66 in 2013 to 4.75 in 2021, according to Wu Weihong, deputy director of the city's ecology and environment bureau.

Sand-dust weather is one of the reasons why Lanzhou's air quality does not meet the standard. In 2021, Lanzhou was affected by sand and dust for 44 days.

The city has made efforts to reduce coal burning, tap the emission reduction potential from industrial sources, and strengthen dust pollution  control, Wu said.

Air pollution in Lanzhou was once notorious. Since 2013, the city has made continuous efforts in air pollution control and won the Award for Today's Transformative Step 2015 at the World Climate Conference held in Paris.