China's ozone pollution slows down due to a fall in other pollutants

After notable increases over the preceding five years, the upward trend of China's ozone pollution has shown signs of slowing during the 14th Five-Year Plan period (2021-25).

While some key regions have seen downward trends, the national picture still raises concerns, as ozone levels have not yet shown a decisive and effective improvement, according to a draft blue book on ozone.

Unveiled by the Committee on Ozone Pollution Control of the Chinese Society for Environmental Sciences in Beijing on Monday, the blue book said the national average urban ozone concentration over the past decade has followed a distinct two-phase trajectory: a sustained rise, followed by a period of elevated fluctuation.

During the 13th Five-Year Plan period (2016-20), the average annual ozone density across the 339 major cities in the country climbed from 126 micrograms per cubic meter in 2016 to a decade-high of 148 mcg/cubic m in 2019, the blue book said.

Though the density edged down to 138 mcg/cubic m in 2020, the overall trend remained significantly upward, it said.

Since the start of the 14th Five-Year Plan, it said the national average density of ozone has ranged between 137 and 145 mcg/cubic m, registering 138 mcg/cubic m in 2025, with no clear upward or downward trend.

In contrast to ozone, other air pollutants have shown a sustained downward trend overall from 2016 to 2025, it said.

It said ozone remains one of the foremost constraints on urban air quality attainment in China, with its role as the primary pollutant growing ever more pronounced.

In 2025, among the days with air quality exceeding national standards across the country, days with ozone as the primary pollutant accounted for 48.9 percent of the total, while days with PM2.5 particulate matter as the primary pollutant accounted for 50.4 percent, it said.

In the Beijing-Tianjin-Hebei cluster, days with ozone as the primary pollutant accounted for 54.7 percent of the days with excessive air pollutants, it said. For the Yangtze River Delta, the proportion stands at 58 percent, and in the Pearl River Delta, 96.6 percent.