Doubts over vehicle control

Although there has been debate on the major causes of smog, local governments have targeted vehicle emissions, hoping less car use will help reduce air pollution.

Higher targets set for emission reduction

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Following the cities of Beijing, Shanghai, Guangzhou and Guiyang, Tianjin Municipality now has rules on vehicle purchases, by capping the number of new license plates that are released. Potential buyers have to get license plates through a monthly lottery or auction.

According to Tianjin's traffic management bureau, more than 150,000 applicants will vie for 9,100 plates through an auction on February 25 or a lottery on February 26.

Like Beijing's traffic control policy that took effect in 2008, Tianjin this year will take one fifth of private cars off the road on weekdays based on the final digit of car plate numbers.

However, policies have attracted criticism.

A research found less than 4 percent of Beijing's PM 2.5, pollutant airborne particles smaller than 2.5 microns in diameter, was contributed by vehicle emissions.

Zhang Renjian, a researcher with the Institute of Physics at the Chinese Academy of Sciences, released the findings in December, sparking wide debate.

Although the academy later clarified that the research "seriously underestimated" the impact of vehicle emissions to air quality, experts believe controlling the number of cars on the road is not a solution to the lingering smog.

"Smog cannot be solved by capping the number of cars or restricting them from running," said Niu Wenyuan, an expert on sustainable development and a consultant for the State Council, China's cabinet.