Ozone pollution in Beijing
Ozone has overtaken PM2.5 to become the top air pollutant in Beijing, Tianjin and Hebei in nearly half of the bad air days in summer, according to an air quality report released by the Ministry of Environmental Protection.
The levels of ozone in some districts of suburb Beijing have surpassed 300 micrograms per cubic meter in recently days, as an average level of more than 200 micrograms in eight hours is defined as "pollution".
Ground level ozone is created by a chemical reaction between sunlight and emissions from vehicles, thus hot, sunny days see a rise in the pollutant.
Inhaling ozone can irritate the lungs and cause wheezing and coughing.