New research conducted by Chinese scientists cast doubt on the belief that coal burning is the main source of sulfate, one of the major contributors to air pollution in China.

By analyzing coal samples collected from several regions in China, including North China's Shanxi Province and East China's Anhui Province, scientists discovered that it is unlikely that the strange signal in sulfates in the aerosols originated from burning coal, Shen Yanan, a head of the research program and an expert at University of Science and Technology of China, told the Global Times on Thursday.

The research was jointly conducted with scientists from the University of California,San Diego, and the results were published in the Proceedings of the National Academy of Sciences (PNAS) in the US on Monday.

Since burning coal accounts for about 95 percent of sulfur emissions in China, it was widely believed that sulfate, a major constituent of haze in China, might have also come from coal burning, the article said.

Instead, "it is probable that sulfate is produced from the burning of other biomass such as wheat straw," Shen said. "More evidence and research will be required to reach that conclusion, but the findings provided a new way of investigating where the haze came from and how to mitigate air pollution," Shen noted.

Wang Gengchen, a research fellow at the Chinese Academy of Sciences' Atmospheric Physics Institute, said that the source of sulfate and other pollutants depends on the energy structure in different regions.

It also depends on the kind of coal used that may contain different amounts of sulfur. "Whether sulfur removal technology is properly used in the regions is another factor," Wang said.

Generally speaking, coal burning "still should be the focus when dealing with haze in China," Wang noted.

Shen and his team also developed a new method of tracing the haze by tracking 35S, a sulfur isotope.

35S only forms in the upper atmosphere and has a half-life of 87 days, which is ideal for tracking atmospheric processes, Shen said.

Shen recommends that the new method should be widely applied in tracking haze movements that can help in resolving haze-related disputes between countries.

Japan and South Korea said their haze came from China, media reported.

But South Korean experts attributed 40 percent of their country's haze to China.