Ten to 15 years ago, squamous cell carcinoma took the lion's share of all lung cancer cases, roughly 60 percent, he said. "At that time, most of the sufferers were smoking males, who are at high risk."

The incidence of lung cancer has surged in recent decades.

For instance, in the 1960s the incidence of lung cancer in Guangzhou, Guangdong province, stood at 7 per 100,000 people. That surged to 70 per 100,000 in 2005, according to local health data.

Some lung disease experts suspect the rise might be related to PM2.5, but more research is needed to know for sure.

Xue said more government research funding and projects in the field are needed.

Internationally, small-scale studies have associated air pollution exposure with lung cancer, but a direct link has not yet been confirmed with large, long-term studies, he added.

Industrialized countries saw a rise in the proportion of adenocarcinoma before China, according to Xue, who said lung adenocarcinoma is now the most common type of lung cancer.

Squamous cell carcinoma has decreased over recent decades in Western countries due to an ever decreasing smoking population, he added.