BEIJING -- China's atmospheric environment saw improvement in 2021 as the country continued its efforts to ensure air quality, a meteorological official said Friday.

In 2021, the average density of PM2.5, a key indicator of air pollution, decreased 9.1 percent year on year to 30 micrograms per cubic meter in China, said Xue Jianjun, deputy head of the National Meteorological Center.

The average concentration of ozone eased 0.7 percent from that in 2020 to 137 micrograms per cubic meter last year, he added.

Xue also noted that efforts to contain acid rain proved to be effective in most regions nationwide during the period.

However, there were occasional heavy-pollution days because of adverse meteorological conditions, Xue said, stressing that implementation of air pollution prevention and control measures should not be relaxed.