With the arrival of summer, ozone has overtaken PM2.5, fine particles with a diameter of less than 2.5 microns, to become the top air pollutant in Beijing, Beijing Youth Daily said on Thursday.

Statistics released by the Beijing Municipal Environmental Monitoring Center show that starting on Tuesday this week, air pollution caused by ozone in Beijing has been more serious than pollution caused by PM 2.5.

At 4:00 pm on Wednesday, the average level of ozone in Beijing was recorded at 250 micrograms per cubic meter, higher than the national standard of 200 micrograms per cubic meter.

High levels of ozone are irritating to the eyes and may cause damage to the lungs. Ozone level typically reaches its peak in mid- to late afternoon, and indoor ozone levels tend to be lower than outdoor levels, so local residents are urged to limit outdoor activities during peak ozone hours.

Ozone is complicated and hard to control, according to Xie Shaodong, a professor at Peking University's School of Environmental Sciences.

High levels of ozone can also enhance the process of PM2.5 concentration, Xie added.

Since the major precursors of ozone are oxynitride and volatile organic compounds, which mainly come from vehicle emissions, the restriction of vehicle volume and upgraded fuel standards can help control ozone pollution in the capital, according to Pan Tao, president of the Beijing Municipal Research Institute of Environmental Protection.