As Beijing prepares to raise its car emission standards on Feb 1, neighboring areas have been using poorer quality fuel that threatens to undermine the capital's anti-pollution efforts, experts said.

Cities nationwide have been urged to adopt stricter automobile emission standards to ease the murky haze and improve air quality.

Hao Jiming, an academic at the Chinese Academy of Engineering, said that raising the quality of gasoline and diesel and emission standards is crucial to improving the air.

"The clean fuel and clean vehicles are the most efficient and economical measures to improve the country's air," Hao, also a professor at Tsinghua University's School of Environment, said at a conference on Thursday.

Beijing announced earlier that it has prepared a higher standard of fuel with a sulfur content of no more than 50 parts per million to go with the stricter emission standards.

The stricter standards adopted by Beijing are expected to reduce nitrogen monoxide emissions by 40 percent. The concentration of PM2.5, or particulate matter smaller than 2.5 micrometers in diameter, is also expected to decrease.

But in neighboring cities, gasoline has a sulfur content around 150 ppm, and diesel has a sulfur content of about 2,000 ppm.

"That poorer quality of fuel will hinder the capital's efforts to improve the air," said Yue Xin, director of the vehicle fuels and emission laboratory under the Chinese Research Academy of Environmental Sciences.

Zhao Jingwei, a Beijing lawyer specializing in environmental protection, echoed Yue's sentiments, saying that "it requires joint efforts to crack the nut".

Michael P. Walsh, chairman of the International Council for Clean Transportation, said that the capital, as well as other cities nationwide, should learn from the experiences and lessons abroad.

"Los Angeles heavily relies on private vehicles, and the geographical condition there is not beneficial for the diffusion of the pollutant, but thanks to the strictest automobile emission controls worldwide, the city still enjoys fresh air," he said.

Dense fog and smog that blanketed parts of North China for several days resulted in intense complaints from the public.

Some blamed the increasing car ownership in Beijing, which now has 5.2 million vehicles, with about 200,000 new ones being added every year.

Walsh said the continuous murky haze that enshrouded the capital would not have been as bad if cleaner fuel and vehicles had been adopted across the country.

"China has made great strides but has recently hit a major roadblock. Increasing fuel quality can greatly improve the city's air," he said.

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