The metropolis also saw its average ozone concentration decrease to 149 micrograms per cubic meter in 2021, marking the first time the readings for PM2.5 and ozone for the city reached the level-II national standard simultaneously.

2021 年，北京的平均臭氧浓度降至 149 微克/立方米，这标志着北京的PM2.5 和臭氧首次同时达到国家二级标准。