SHIJIAZHUANG, Feb. 14 (Xinhua) -- Air quality keeps improving in Zhangjiakou, one of the competition zones of the Beijing 2022 Olympic Winter Games. The city ranked first in Hebei province last year in terms of air quality, according to the Ecological Environment Bureau of Hebei.

Located some 200km northwest of Beijing, Zhangjiakou will host snowboarding, freestyle skiing, cross-country skiing, ski jumping, Nordic combined and biathlon competitions at the 2022 Winter Games.

According to a government report on Zhangjiakou, its average air quality index reached 4.11 in 2018, down by 0.07 year on year, and the average concentration of PM 2.5, or fine particulate matter, was 29 micrograms per cubic meter, 2 micrograms less than in 2017. For five consecutive years, Zhangjiakou is rated city with the best air quality in the Beijing-Tianjin-Hebei region.

Zhangjiakou is also set to be Beijing's water conservation area and ecological environment supporting area. An unprecedented 400,000 hectares of trees were planted in Zhangjiakou last year, accounting for three-fifth of the total increment increase in Hebei province.

A series of measures have also been taken to improve the overall environment in Zhangjiakou. 105 mines were closed and 4,518 new energy buses were launched last year.