Scientists search for clear answers on smog(3)

Customers select air fi lters in Beijing. Poor air quality has boosted sales of various fi lters in many parts of China.

However, the Global Burden of Disease Study 2010, a survey conducted by scientists across the globe, came to the conclusion that air pollution was a major factor in the premature deaths of approximately 1.2 million people in China in that year.

The authors of the studies attributed the wide fluctuation in their findings to a number of factors, such as the pollutants targeted; PM2.5, PM10 or PM1. Also, the global burden report included the rural population, while the joint study did not.

But they all admitted that their findings may be inaccurate because the calculations for the exposure-response functions they employed were based on overseas studies rather than being generated by cohort studies - observations conducted by following a group of people over a given time scale - in China.

Fudan University's Kan said the accurate exposure-response function of any given region should be determined by a thorough cohort study into the effects of air pollution on the health of the local population, a process that could take 12 years, or even longer.

However, cohort studies are expensive and time-consuming, so instead of conducting their own studies, Chinese researchers have to rely on results from the two most-famous cohort studies in the US. One, conducted by Harvard University in the 1970s, included more than 8,000 people in six cities, while the other, conducted by the American Cancer Society from 1982 to 1998, involved approximately 500,000 people.

"To get the most-accurate number of premature deaths caused by air pollution in China, a domestic cohort study covering a large-enough sample of the population and a long life span is a precondition," said Kan.