Ozone density poses challenges for China's air pollution targets

Despite an increase in ozone density across the country, safety hazards from the air pollutant are still "controllable" and "preventable", environmental officials said. The harmful gas, however, has posed challenges for the country as it looks to realize its target for air pollution control.

While the average density of the other major air pollutants either all declined or changed little in the 337 major cities across the country in 2019, the concentration of ozone went up by 6.5 percent year-on-year to 148 micrograms per cubic meter, according to a report on the country's ecological and environmental condition published by the Ministry of Ecology and Environment on Tuesday.

"In recent years, ozone pollution has been increasingly growing in the country … It has been the primary pollutant affecting air quality during summer," said Bai Qiuyong, head of the ministry's environmental monitoring department, during a news conference on Tuesday.

Ozone was the primary pollutant in almost 42 percent of days with excessive amount of air pollutants in 2019 in these major cities－second only to PM2.5 particulate matter, which was blamed for 45 percent of such days, he added.

While the ozone layer helps shield the Earth from harmful ultraviolet radiation, the gas is harmful to people's health and could damage the lungs and result in shortness of breath even if people breathe in a relatively low amount of it.

Bai, however, said the density of the air pollutant is still below the national standard of 160 mcg/cubic meter, which is the same as the World Health Organization's standard.

"Usually, ozone density exceeds the national standard only after noon when the temperature is high and the sunshine is strong," he said.

"The hazards of ozone to people's health is preventable and controllable if people stay at home and minimize outdoor activities as much as possible during that time."

However, the increase of ozone density, which is occurring against the backdrop of global warming, has posed challenges for the country in its effort to meet its air pollution target.

The country plans to increase the number of days with fairly good air quality in the 337 major cities by 3.3 percentage points to 79.3 percent during the 13th Five-Year Plan (2016-20). Despite the number having reached 79 percent by the end of 2018, the sharp increase in ozone density last year has "added difficulties" to accomplishing the goal, said Liu Bingjiang, head of air quality management at the ministry, during a news conference in May.

The sharp increase occurred because seven provinces suffered heat waves and drought that happen on average once every 50 years, he explained.

Sunlight and high temperature could trigger chemical reactions between primary air pollutants such as nitrogen oxides and oxygen, which will form ozone.

"From January to March, the number of days with fairly good air quality increased by 5 percent year-on-year. This has laid a good foundation for ozone pollution control work for the rest of the year," he said.

"As long as no extreme weather happens, we have the resolution and confidence to realize the target."

Climate experts, however, have warned of a hotter flood season from May to September, a major period for ozone pollution.

Zhou Bing, a chief expert with the National Climate Center, said temperatures in the country will generally be higher than in normal years, and some regions will suffer high temperatures and heat waves during the May to September period.