Smog stalling return of overseas Chinese(2)

"The causes are various and complicated. We must analyze both sources and dispersion of smog," said Zhao Chuanfeng, a professor at Beijing Normal University's College of Global Change and Earth System Science.

Zhao came to the United Stated in 2002 and worked in California after graduation. He returned to China not long ago.

He pointed out that coal fires, traffic emissions and atmospheric dust all contribute to air pollution.

"Smog-forming pollutants come from many sources, so we need to figure out their relative contribution by building observing sites and dispersion models," according to Zhao.

One person who has attempted this breakdown is Yan Hao, deputy director of the environmental watchdog in Xi'an, which had only five days with good air quality in the first quarter of this year.

"Coal fires, traffic emissions and atmospheric dust account for 75 percent of the total smog-forming pollutants in Xi'an," said Yan.

Another 10 percent of the pollutants were contributed by organic waste gas from sources including gas stations, auto repairs and home decorations, he added. "And we have more than 10,000 restaurants emitting cooking fumes and consuming fuels."

LONG WAY TO GO

Xiao Hang came back from Canada last year and became a researcher at the Institute of Urban Environment under the Chinese Academy of Sciences.

"I think heavy smog will affect China's international image," he said. His friends in Canada regularly discussed this issue. While they care about development opportunities in China, environment and health have come to assume greater important in recent years.

Like Xiao Hang, 40-year-old Fu Yu left Harvard University and returned to China this year.

"My son was taught to conserve energy and protect the environment in an American kindergarten," he said. "But I found in our nation, many people still don't know much about that."

But the government is aiming to correct this ignorance. In September, China announced an action plan to tackle air pollution, aiming to cut the density of inhalable particulate matter by at least 10 percent in major cities nationwide by 2017.

"Xi'an is shutting down high-polluting factories and promoting environmentally friendly energies," according to Yan Hao.

The total number of vehicles in Xi'an is about 1.7 million, consuming 1.35 million tonnes of oil and emitting 300,000 tonnes of key pollutants each year, an amount that is equal to the city's level of industrial discharge.

In response, public security departments have toughened checks on vehicles, including phasing out older ones.

Lin Yanluan also recalled that when he stood in the streets of New York, the smell of vehicle exhausts was not as pungent as in Beijing.

"So improving the quality of gasoline is also very important," Yan observed.

In Xi'an, more than 70 of the city's 600 gas stations have switched to cleaner fuel to meet the national level-IV standard, which allows for the sulphur content of fuel to be no more than 50 parts per million (ppm).

"Experts said this standard might reduce vehicle exhaust fumes by 10 percent compared to the level-III standard with sulphur content as high as 150 ppm," Yan said.

Xiao Hang now lives in China's coastal city of Xiamen. "The air quality is good here, but perhaps these cities will face the same problem someday," he said.

It is a problem which big cities in industrialized countries have repeatedly come up against for decades. China still has a long way to go, Xiao added.