While China reduces air pollution, an invisible killer appears

According to the World Health Organization, China's air is already a public health crisis. About one million deaths are attributable to air pollution each year. But as the government strives to dispel the gray haze that covers the country's cities, an invisible killer is raising its ugly head: ozone. The public health experts in the country are worried.

"China should pay more attention to the fight against the ozone layer," said Zhang Junfeng, professor of global and environmental health at Duke University and director of the China-US Regional Research Center on Combating the Ozone Layer. Ozone pollution, the first 2016. "Once the ozone enters the human body, it causes considerable damage to the immune system and aggravates existing cardiovascular and respiratory problems."

Ozone is better known as a layer of gas in the Earth's atmosphere that protects humans from harmful ultraviolet rays, which can cause cancer and other health problems. Indeed, China has been criticized globally for its inability to control national emissions of chlorofluorocarbons – or CFCs – chemicals that deplete global ozone levels and increase health risks. .

However, the fact that too much ground level ozone also poses a threat to public health is less well known. The air containing high concentrations of ozone can damage the cells of the lungs and other organs. According to a study on the long-term ozone exposure published in 2017 by the journal Environmental Health Perspectives in China, about 316,000 adults died in 2010 from respiratory diseases caused or aggravated by environmental pollution. 39; ozone. In addition, about one-quarter of all ozone-related ozone-related deaths worldwide occur in China.

Ozone accumulates when airborne nitrogen oxides – mainly produced by coal combustion and vehicle emissions – react with volatile organic compounds (VOCs), organic chemicals that evaporate easily, even at room temperature. Although the Chinese government's air pollution control policies have reduced atmospheric nitrogen oxides since 2012, they are less effective at controlling VOCs, resulting in ground-level ozone build-up.

According to Zhang, the problem of ozone in China is aggravated by the fact that public debates on air pollution focus mainly on so-called atmospheric particles – microscopic solid or liquid particles suspended in the air that contribute smog visible in cities. Particles less than or equal to 2.5 and 10 microns in diameter – known as PM 2.5 or PM 10 – are known to be life-threatening, leading to cancer, heart attacks and respiratory diseases. As a result, the Chinese government has implemented a series of measures to reduce atmospheric PM 2.5 levels and more, while efforts to reduce ground-level ozone have become bogged down.

"The public is well aware of how PM 2.5 is causing significant air pollution, and the authorities have worked hard in recent years to control PM 2.5 and PM 10," said Zhang. "It is obvious that these pollutants have fallen. But ozone pollution (…) does not attract as much attention from the public as the government, because it is much less visible at the beginning. "

As a result, China's air quality policies prioritize PM 2.5 reductions ahead of ozone reductions, said Hao Jiming, a professor of environmental engineering at Tsinghua University in Beijing. "Currently, China's standards for safe concentrations of PM 2.5 in the atmosphere are 3.5 times higher than the WHO guidelines for air quality," says Hao, a goal that some parts of the country are failing to reach despite the extra room for maneuver. At the same time, national standards for ground – level ozone are only 1.6 times higher than those of the WHO and are broken in a less dramatic way, focusing more attention on PM 2.5, adds Hao.

Last month, scientists from Harvard University and Nanjing University of Science and Technology released a document showing how China's PM 2.5 war had unexpectedly led to pollution by the ozone layer. Normally, the presence of PM 2.5 in the air disrupts chemical reactions between free radicals producing ozone. As PM 2.5 levels decrease, these reactions become more likely and therefore produce more ozone. The negative effects of the drastic reduction of PM 2.5 on ozone pollution are particularly noticeable in areas such as the North China Plain, a former industrial region that has been a key objective of reducing ozone pollution. pollution in recent years.

In an interview in January, Daniel Jacob, one of the co-authors of the newspaper, drew attention to the uniqueness of the ozone problem in China. "We have not seen that happen elsewhere, because no other country has acted so quickly to reduce [PM 2.5] emissions, "said Jacob. "It took China four years to do what took 30 years in the United States"

In their paper, Jacob and his colleagues urged China to put in place effective measures to reduce ozone pollution by controlling the release of its precursors – nitrogen oxides and VOCs. But Zhang, the professor at Duke, believes that reducing ozone pollution can prove even more difficult than particle control, in part because it's hard to identify the Origin of pollution by ozone.

"Ozone trends are different in different parts of China. Understanding which precursors is causing ozone formation in a city or region is the first step towards controlling ozone, Zhang said, adding that research on ozone Ozone pollution was sorely lacking compared to that on PM 2.5. "In many areas, we still do not know what really increases the levels of ozone," he adds.

Without strong ozone control measures, many Chinese will likely face greater health risks. Across the country, climate change and global warming are prolonging and intensifying periods of warm weather during which ozone concentration is increased. At the same time, the Chinese population is aging and is more vulnerable to the adverse effects of ozone pollution on health.

"If climate change continues at the current rate, ozone pollution will lead to higher mortality rates in the future," said Chen Kai, a postdoctoral fellow at the Alexander von Humboldt Foundation in Germany. Chen's research, in collaboration with Columbia University, shows that China's mortality rates linked to short-term ozone exposure could quadruple in the next 40 years, mainly due to global warming. and the aging of the population.

China's latest three-year plan to reduce air pollution, published in July 2018, contains certain provisions related to ozone control, such as compelling manufacturers to repair and replace VOC emitting equipment and to apply legal upper limits of adhesives. And in the Yangtze Delta, experts are already partnering with government authorities to combine PM 2.5 control with protection against excess ozone by reducing industrial emissions, vehicle exhaust gases and the burning of coal.

"If China does not pay enough attention to ozone pollution now, it will be difficult to fight it in the future," Zhang said.

Publisher: Matthew Walsh.

(Header image: a man wearing a mask during a day of extreme pollution in Beijing, December 21, 2015. Wang Zhao / AFP / VCG)