Although a rainfall washed away the heat in Beijing, the Beijing Municipal Environmental Protection Bureau predicts that ozone will be the primary pollutant in Beijing's air on June 4. Beijing is not the only city affected; according to the Ministry of Ecology and Environment, due to persistent high temperatures and southerly winds near the ground, most of the Beijing-Tianjin-Hebei region, most of Shandong, and parts of northern Henan may experience light to moderate ozone pollution.

　　It is predicted that from June 4th to 15th, ozone will be the primary pollutant in the Yangtze River Delta, South China, Northwest, and Northeast regions of China.

　　Why does ozone appear when the weather warms and the sun shines? What is the current status of ozone pollution in China, and how should it be governed and controlled?

　　Ozone pollution hidden beneath the blue sky and white clouds

　　Where does the low-altitude ozone near the ground come from? Academician Tang Xiaoyan of the Chinese Academy of Engineering and professor at Peking University explains that when the temperature is high and the sunlight is relatively strong, nitrogen oxides and volatile organic compounds (VOCs) in the atmosphere undergo photochemical reactions under ultraviolet irradiation, generating ozone.

　　Therefore, summer, with its clear skies, bright sunshine, and strong ultraviolet radiation, is particularly prone to ozone pollution. Ozone at room temperature is a light blue gas with a peculiar odor; often, you see blue skies and white clouds, yet ozone levels exceed standards.

　　"Ozone is a strong oxidant; it is not only harmful itself, but its atmospheric mass concentration also reflects the oxidizing capacity of the atmosphere, that is, the ability to generate secondary pollutants. Therefore, to control or reduce ozone pollution and atmospheric oxidizability, it is necessary to simultaneously reduce the emissions of nitrogen oxides and VOCs, achieving synergistic control of pollutants." said Tang Xiaoyan.

　　Ozone pollution in China is showing a year-on-year and month-on-month upward trend

　　According to the ozone monitoring results released by the Ministry of Ecology and Environment at the May regular press conference: In 2017, the average concentration of ozone in the ambient air of 338 cities in China was 149 μg/m³, an increase of 8% year-on-year and 11.2% compared to 2015. From 2015 to 2017, the proportion of exceedance days with ozone as the primary pollutant in 338 cities was 16.9%, 22.5%, and 33.4%, respectively, showing a year-on-year upward trend. In the first four months of 2018, the average ozone concentration in 338 cities was 86, 104, 134, and 157 μg/m³, showing a month-on-month upward trend.

　　"Ozone pollution in China exhibits regional characteristics and is concentrated mainly in south-central Liaoning, Beijing-Tianjin-Hebei and surrounding areas, the Yangtze River Delta, the Wuhan urban agglomeration, the Guanzhong region of Shaanxi, and the Chengdu-Chongqing and Pearl River Delta regions." Liu Zhiquan, director of the Environmental Monitoring Department of the Ministry of Ecology and Environment, said that ozone pollution in China is mainly light and no serious pollution or "off-the-charts" levels have occurred.

　　Continuously promoting the synergistic reduction of nitrogen oxides and VOCs

　　Liu Zhiquan said that the three main reasons for the current prominent ozone pollution problem are: large emissions of its precursors—nitrogen oxides and VOCs, especially VOCs with multiple and dispersed emission sources, which have not been effectively controlled; high temperatures and strong sunlight; the active nature and complex generation mechanism of ozone, with the reduction of nitrogen oxides and VOCs possibly leading to an increase in ozone concentration due to disproportionality.

　　"Based on the experience of developed countries in ozone pollution control, as long as the reduction of nitrogen oxides and VOCs continues, ozone concentration will gradually decrease in the long term; in the short term, ozone concentration may still fluctuate significantly due to weather, the ratio of precursor concentrations, and other factors." said Liu Zhiquan.

　　Liu Zhiquan said that China will strengthen the governance and control of ozone pollution in the next steps. Measures include accelerating the construction of photochemical monitoring networks, conducting routine VOCs monitoring in key regions and cities, strengthening supervisory monitoring of VOCs emissions from industrial parks and key pollution sources, clarifying the sources of ozone and the main influencing factors to provide decision support for ozone pollution control; promoting the synergistic governance of ozone and PM2.5 pollution; strengthening the governance of key industries and sectors in the emission of nitrogen oxides and VOCs, especially addressing the shortcomings in VOCs governance. "We are now accelerating the pace and increasing the intensity of governance. The governance of VOCs is large and extensive, including not only industry but also living sources, including decoration coatings and catering, all of which have VOCs emissions; governance will take time."