Heavy smog obscures the view of downtown Harbin, Heilongjiang province, on Monday. KIM KYUNG-HOON / REUTERS

The health effects of outdoor air pollution can only be assessed after long-term monitoring and quantitative data analysis, a spokesman for the country's top health authority said.

Mao Qun'an, spokesman for the National Health and Family Planning Commission, said in a news conference on Tuesday that the authority's monitoring of the health effects of outdoor air pollution could yield results only after a long period. The monitoring began in late 2013.

In October, the authority announced a plan for establishing a monitoring network to study outdoor air pollution's effects on health in the next three to five years.

In December, Chen Zhu, former minister of health, wrote in an opinion piece in the British general medical journal The Lancet that a 2010 study finding that at least 350,000 people in China die prematurely each year as a result of outdoor air pollution "might overestimate the health effects of outdoor air pollution".

The study, conducted by the World Bank, World Health Organization and the Chinese Academy for Environmental Planning, concluded that between 350,000 and 500,000 people die prematurely annually as a result of outdoor air pollution.

Chen, who was elected vice-chairman of the 12th National People's Congress Standing Committee in March, said those findings are "a maximum international estimation".

Chen referred to research from the Chinese Academy for Environmental Planning, which concluded that 200,000 premature deaths a year would be prevented if the annual level of PM10 (particles with a diameter of 10 microns) meets the highest level of the China National Ambient Air Quality Standards.

According to the Global Burden of Disease Study 2010, about 1.2 million people in China died prematurely and 25 million disability-adjusted life-years were lost in 2010 as a result of air pollution.

Wang Wuyi, an environmental and health researcher at the Chinese Academy of Sciences, said more data is needed on the effects of air pollution on people's health.

"The country only started monitoring the level of PM2.5 (particles with a diameter of 2.5 microns) and its effect on health since the start of last year in limited areas such as Beijing. Before that there were no statistics available on the relationship between PM2.5 and health," he said.

Yu Fang, a researcher at the Chinese Academy for Environmental Planning, who was part of a 2013 study on outdoor pollution and health in China, said current research on the health effects of long-term exposure to air pollution can only refer to similar studies in the United States, due to a lack of relevant studies in China.

"But we do have domestic studies on short-term exposure, and other studies related to ecology," she said.

"We have done tests that show if five to six people each smoke a cigarette indoors, the air pollution level would be more severe than a heavy smog day," said Mao Qun'an, the spokesman, adding that the authority will unveil a regulation on smoking indoors this year.

The authority's efforts to control smoking indoors have been impeded by a lack of public awareness of the harmful effects smoking has on health.