Fog vapor in downtown Shanghai contains cancer-causing chemicals, researchers said yesterday.

Fudan University scientists compared vapor from the city with that from well-known scenic area Mount Huangshan in Anhui Province.

The Shanghai fog vapor was yellow-tinged and contained contamination, while the vapor collected from Huangshan was pure and clear.

Researchers found carcinogenic polycyclic aromatic hydrocarbons (PAH) at levels ranging 0.03 micrograms to 6.67 micrograms per liter of fog vapor in Shanghai.

This is higher than in some domestic and overseas areas, researchers said.

Burning fossil fuel is the main cause of PAHs in urban Shanghai, said Chen Jianmin, professor of Fudan University's Depart of Environmental Science and Engineering.

The findings are published in the Journal of Environmental Monitoring.

Meanwhile, the city is considering relocating the Gaoqiao factory zone in Pudong, following a series of explosions, fires and leaks.