PM2.5 will give way to PM10 as major component of coming smog

Ozone is forecast to be one of two major contributors to the smog expected to settle in areas of the Beijing-Tianjin-Hebei province region early this month, the top environmental authority said on Wednesday.

It will also be the only major pollutant for mild or moderate air pollution expected to occur in many other parts of the country, the authority said.

At the start of August, air pollution is expected to develop in the central and southern parts of the Beijing-Tianjin-Hebei region, and some areas may experience heavy air pollution because of unfavorable meteorological conditions for dispersal, combined with the lingering heat wave, according to a statement from the Ministry of Ecology and Environment released late on Wednesday.

Ozone will remain continuously, although PM2.5 - tiny particles that can penetrate the lungs and enter the bloodstream - will also contribute to the widespread pollution in the region until Monday, with some areas heavily polluted. Also, PM10 will replace PM2.5 as one of the two major pollutants that mainly affect the central and southern parts of the region until Aug 10, it said.

The ministry said in a statement on Wednesday that it found 5,204 environmental violations from June 11 to July 8 in an air pollution control inspection in 28 major cities in the Beijing-Tianjin-Hebei cluster.

The heads of five county-level administrative areas in the region, including Beijing's Tongzhou district, have been summoned by the ministry to answer for their poor performance in air pollution control.

Ozone will also affect most other regions. In the Yangtze River Delta, for example, the mild ozone pollution that was present in most parts of the region on Wednesday will be dispersed by Tropical Storm Jongdari between Thursday and Saturday. The pollution, however, will show up again in central and northern parts of the region from Sunday until Aug 9, the ministry said.

Ozone occurs in two layers of the atmosphere: the troposphere, the layer closest to the Earth's surface, and the stratosphere, the layer that extends upward from about 9 to 48 kilometers.

The gas, however, can be both good and bad. In the stratosphere, ozone protects life on Earth from the sun's harmful ultraviolet rays. In the troposphere, however, ozone is a pollutant that could trigger a variety of health problems, particularly for children, the elderly and people troubled by lung diseases.

Most ozone in the troposphere is formed by a chemical reaction when sunlight interacts with nitrogen oxides and other organic compounds generated by coal-burning, vehicle exhaust and some natural sources.

Zhao Yingmin, vice-minister of ecology and environment, said in June that the country will roll out new guidelines to control ozone pollution, which has been rising steadily since 2015, by stepping up the controls of nitrogen oxide and volatile organic compounds.

Meanwhile, the ministry launched a nationwide campaign on Tuesday to crack down on companies illegally producing substances listed in the Montreal Protocol on Substances that Deplete the Ozone Layer.