In major Chinese cities, drastic measures were taken against the particulate matter pollution. With success. The burden with the small particles could be significantly reduced. However, this has an unforeseen side effect: The burden of ozone has increased significantly.
Unexpected Effect of Decreasing Particulate Pollution
A research group led by Ke Li of Nanjing University of Information Science and Technology has evaluated data from 1000 measurement stations from the years before 2013 to 2017. China's official air pollution action plan came into force in 2013. The data show a correlation between the decline of particles less than 2.5 microns in diameter and increasing ozone concentration.
The researchers see the change in atmospheric chemistry as the cause of this effect. The fine dust particles capture the oxygen radical HO2. This is an intermediate in ozone formation. The fewer particles of dust in the air, the more radicals are available for the formation of ozone. Since 2013, particulate matter concentrations in Chinese cities have been reduced by almost 40 percent. In return, however, the ozone concentration increases by about 2 to 6 micrograms per cubic meter of air. This is problematic because ozone pollution in eastern China has long been a significant problem. The concentration is sometimes well above the specified limits.
The working group emphasizes that the results are no reason to stop the measures against particulate matter. The measures must be continued in order to further reduce the burden. At the same time, however, a stronger focus must be placed on the causes of ozone pollution. These include on the one hand nitrogen oxides and on the other hand volatile organic compounds. Both pollutants come to a large extent from internal combustion engines. Under the influence of UV light, these substances produce ozone.