Beijing health authorities have launched a pilot project to test for the rate of cancers in the city, and will offer free diagnostic tests to those surveyed who are considered to be at particularly high risk.

The project was announced after Beijing Health Bureau (BHB) released a list of the top five cancers with high incidence occurring in Beijing.

The rate of lung cancer is the highest of all cancers, and smog and smoking have been specifically cited as causes of it, BHB said.

While some medical experts have stated they have yet to see evidence of an explicit link between PM2.5 pollution and lung cancer, others said there could be a connection. However, smoking is still the biggest cause of lung cancer, and the city has done nothing to control the level of smoking.

Du Hong, deputy director of the disease prevention and control department of BHB, said Beijing is the trial city for the five-year program before it goes nationwide.

"The five cancers that have the highest incidence in Beijing are lung, breast, colon, liver and upper gastrointestinal tract cancers," she said.

"Smoggy weather and smoking are triggers of lung cancer," she said, noting that other factors such as work stress and unhealthy lifestyles are also triggers.

The program aims to raise awareness of the importance of early cancer diagnosis for more effective treatment.

"There will be 50,000 permanent residents of the city aged from 40 to 74 involved in the survey conducted by the district health bureaus of nine districts," said Du. The program for this year started in November 2012 and will end in June. 

Cancer is now the number one cause of death in Beijing. The BHB would not give out updated figures Monday, but the latest available information, figures from 2001 to 2010, suggest that 104 Beijing residents were diagnosed with cancer every day by 2010, according to Beijing cancer prevention and control office in April 2012. The cancer rate increased from 171 per 100,000 people in 2001 to 302 per 100,000 in 2010. Lung cancer is most prevalent in males, and breast cancer in females.

Cui Xiaobo, professor at Capital Medical University, agreed the government should put more effort into tackling the causes of cancers, but said that PM2.5 might cause respiratory or lung disease but not cancer.

"When PM2.5 reaches over 900 micrograms per cubic meter, it is equal to two lit cigarettes in a room," he said.

Cui noted that smoking is still the leading cause of lung cancer.

"PM2.5 could also be found indoors but its substance might not cause cancer," he said. Cui said that the government has spent billions of yuan on tackling the environment while investing little on banning indoor smoking in public areas.

Jiao Shufang, chief physician at the Beijing Centers for Diseases Control and Prevention, also said there was no proven link between air pollution and lung cancer. 

"I haven't read any reports suggesting air pollution or smog is connected to lung cancer. Smoking, as ever, is the major cause," she said.

Wang Ning, vice director of Beijing Institute for Cancer Research, said there is research showing that toxic particles in PM2.5 might cause cancer.

"PM2.5 contains heavy metals like lead that might attach to the lining of the lungs," she said, noting that these substances are small and cannot be expelled by coughing.

"Yet whether the PM2.5 in Beijing might cause lung cancer is uncertain because local scientific research is lacking," she said, noting that 10 years of experimentation is needed to prove a  possible causal link to lung cancer.

An assessment of health jeopardy and economic losses caused by PM2.5  pollution conducted by Peking University and Greenpeace, published in December 2012, said that PM2.5 caused the deaths of 2,349 people and 1.86 billion yuan ($299.5 million) losses in Beijing in 2010. It estimated that the death rate would rise to 2,589 in 2012 with economic losses of 2.06 billion.

According to research by the American Cancer Society between 1982 to 1998, whenever the level of PM2.5 increases by 10 micrograms per cubic meter, the death rate of lung cancer will increase by 8 percent, Wenhui Daily reported in February 2012.