Government officials and experts say emissions from cars are a significant factor when it comes to pollution.

The comments come after an earlier report on the major sources of smog which seems to downplay the role of the automobile.

A?report from the Chinese Academy of Sciences determined that motor vehicle emissions account for less than 4 percent of Beijing's hazardous PM2.5 readings.?[File photo]

The report from the Chinese Academy of Sciences determined that motor vehicle emissions account for less than 4 percent of Beijing's hazardous PM2.5 readings.

That finding from the country's top research body seems to be in contrast to what many citizens in the capital believe, that the city's 5.5 million cars are chiefly to blame for the local smog problem.

FANG Li is a deputy director of the Beijing Environmental Protection Bureau.

"The report says secondary inorganic aerosol contributes to 26 percent of the PM2.5, which is largely from car emissions. So I say the role car exhaust plays is more than 4 percent. From the data we have collected, I would say the rate is between 20 and 30 percent."

Professor Zhuang Guoshun from the Department of Environmental Science and Engineering at Fudan University, also says he is worried about the report's findings.

"Industrial pollution levels have been largely unchanged over the past 10 years thanks to desulfuration technology. But during the same period, we've seen sky-rocketing growth in the car industry in cities large and small. So I dare-say car emissions contribute more than industrial pollution nowadays."

A number of measures have been implemented in big cities to reduce car emissions, including limiting the number of cars in use, limiting the issuance of license plates and upgrading petrol standards.

Professor Lin Boqiang, director of China Center for Energy Economics Research at Xiamen University, says these measures are necessary.

"People have the impression that car emissions cause smog because the pollution problem started in big cities like Beijing and Shanghai where there are many cars. But the root cause actually lies in our energy structure, which relies heavily on coal. But reducing car emissions would be effective in the short term."

China has issued a 1.75-trillion-yuan plan, about 300 billion US dollars, to tackle the air-pollution problem, pledging to improve air quality within five years.

Beijing authorities say the city will build four natural gas power stations by the end of this year to replace those currently burning coal.