Air pollution causes 257,000 premature deaths

Some public health experts were skeptical of the claim, saying that because PM2.5 pollution affects human health over time, it may take a decade or two to quantify its effects accurately.

While they shared concerns about PM2.5 pollution's adverse effects on human health, some took issue with the details of the study.

"The country has started to investigate the health effects, but it will take one or two decades to get results based on long-term tracking of some patients," said Zhi Xiuyi, head of the Lung Cancer Diagnosis and Treatment Center of the Capital Medical University.

He said air pollution could exacerbate some diseases, such as those related to the lungs, and lead to delays in recovery, but it's hard to say that PM2.5 pollution was the major factor in a death.

Moreover, some of the 31 used in the study did not release data on PM2.5 in 2013, he said, leading him question the results.

"I think that the results could be inflating the number of deaths related to PM2.5 pollution due to multiple factors," Pan said, although he said it's legitimate to seek understanding about the effects on human health.

Dwight Clark, Medical Director of US-Sino HeartCare in Beijing, said every increase of 5 micrograms per cubic meter of PM2.5 particles means an 18 percent increase in lung cancer.

However, he stressed that no matter what numbers are released from various organizations, the people and governments should notice that air pollution is bad and getting worse.