The country's 35 major cities and municipalities will release detailed analysis of sources of PM2.5 - fine pollutant particles found in the air - by the end of this year to help create more effective ways of curbing air pollution.

Beijing is experiencing its longest spell of hazy days this year, with the air quality index reaching 422 by 4pm on Thursday.

The figure made the day one of “severe” pollution, hazardous to human health, the municipal environment monitoring center said.

To control the frequent smog, Beijing, Tianjin and Shijiazhuang, capital of Hebei province, have released an official report on the major sources of pollution last year.

Shanghai released its report on Jan 7, the latest city to possess a thorough picture of PM2.5 – airborne particles smaller than 2.5 microns in diameter that can penetrate the lungs.

Another six cities, such as Guangzhou in Guangdong province, have finished their research and will release the analysis soon.

The authority will push forward efforts to curb air pollution this year with stricter supervision and better early-warning systems for smog, said Zhou Shengxian, minister of environmental protection.

Analysis of PM2.5 sources can provide specific scientific information on major polluters – what percentage of vehicle exhaust and industrial production are responsible as well as details of pollutants from neighboring areas.

In Beijing, the major source of PM2.5 is from vehicle exhaust, accounting for 31.1 percent. Shanghai suffered a similar problem with 29.2 percent of PM2.5 from exhaust fumes.