Huanglongshan Island in Zhoushan. [Photo/WeChat account: sstour]

Haikou tops the 168 key Chinese cities in terms of the air quality last year, followed by Lhasa, Huangshan, Zhoushan and Fuzhou, according to the Ministry of Ecology and Environment.

From January to December in 2021, days of "A" and "B" classes accounted for 87.5 percent of the whole year in 339 cities above the prefectural level.

The average PM2.5 concentration was 30 micrograms per cubic meter, down 9.1 percent year-on-year.

However, Linfen, Taiyuan in Shanxi province, and Hebi in Henan province presented relatively poor air quality.