BEIJING — China continued to see steady progress in its green transformation of economic and social development, with significant improvement in the ecological environment in 2021.

The following are some related facts and figures from a communique released by the Ministry of Ecology and Environment on May 26.

— Last year, the percentage of days with good air quality was 87.5 percent in 339 cities at and above the prefecture level, up 0.5 percentage points year-on-year. Air quality in 64.3 percent of the cities met standards, up 3.5 percentage points year-on-year.

— For the first time, the annual average concentrations of airborne particles PM2.5, inhalable particulate matter PM10, ozone, sulfur dioxide, nitrogen dioxide and carbon monoxide all saw year-on-year reductions in 2021.

— The average concentration of hazardous airborne particles PM2.5 was 30 micrograms per cubic meter in 2021, down 9.1 percent year-on-year.

— The proportion of surface water at or above Grade III in the country's five-tier water quality system increased 1.5 percentage points year-on-year to 84.9 percent in 2021.

— The national ecological quality index (EQI) came in at 59.77, indicating China's relatively rich biodiversity, a relatively high proportion of natural ecosystem coverage, and a more complete ecological structure.