BEIJING — China is home already to 16 of the planet's 20 most heavily polluted cities — a noxious byproduct of its double-digit economic growth. Now researchers have worse news for the nation's beleaguered lower classes: The air inside their homes is as much as 10 times worse than the prevailing gloom outside.

Seven of 10 homes still burn suffocating coal and wood for heat, and half of Chinese men smoke — a toxic combination of indoor pollution that raises dire questions about the fate of this industrial giant's long-term public health.

Over the next quarter-century, 83 million Chinese will die from lung cancer and respiratory ailments without the reduction of cigarette smoking and indoor fuel-burning, a new study by Harvard's School of Public Health warns.

"In many places in rural China, the roads are good, people now have cell phones and electricity, but residents are still cooking and heating with the same fuel they have used for centuries," said Majid Ezzati, an associate professor of international health and senior author of the study. "And as a result, people are dying."

In an article published this month in The Lancet, a leading medical journal, the Harvard team also concludes that programs to reduce smoking and household use of biomass fuels and coal for cooking and heating could significantly reduce the deaths.

The question, researchers say, is whether the Chinese government has the political willpower to enact sound public health policy.

"This analysis shows that smoking and fuel use, which affects hundreds of millions of people in China, will be a defining feature of future health in that country," said Hsien-Ho Lin, a graduate student in the department of epidemiology at Harvard's School of Public Health and lead author of the study.

Ezzati said he was working a few years ago with a team in central China when his team noticed the high level of deaths, which local residents did not seem to attribute to their household habits.

"People may know when they are in the house and it's very smoky and that it's making them cough — their chest may hurt and their eyes burn. They talk about symptoms and discomfort," he said.

"They know there is something that's not good from their living conditions. But neither in China nor in other parts of the world do these people say: `This is making me die early."'

The World Health Organization in China calls the addiction of the nation's 250 million smokers devastating to public health. "The human suffering, productivity loss on a massive scale and the billions in health costs is an epidemic," said Sarah England, technical officer for the WHO's Tobacco Free Initiative.

"The new Harvard study is a wake-up call, but they only looked at some of the ways smoking kills in China. Cigarettes kill a million a year there. That's the highest death toll in the world by far."

But China's staggering rate of smoking among adult men brings a financial windfall for the government.

"The Chinese government is the largest manufacturer of tobacco in the entire world — larger than all of U.S. tobacco," Ezzati said. "There's a huge economic incentive to continue making cigarettes."

While respiratory illnesses account for three of the top 10 causes of death in China, anti-smoking laws in public places are often not enforced.

Using mathematical models, the researchers determined that the gradual elimination of smoking and biomass fuel burning would avoid 26 million respiratory-related deaths and 6.3 million deaths from lung cancer by 2033.

Solutions include air circular stoves with chimneys ending outside the house and ventilated ground stoves to cut air particulates and carbon dioxide circulating indoors.

But experts within China agree that the government has not publicized the extent of the danger. While indoor pollution is worse in rural areas and smaller cities, even in modern Beijing, once the weather cools, men on bicycle-powered carts wheel stacks of coal bricks for home delivery, peddling alongside European sports cars.

"Awareness needs to be raised. It is important to provide proper education on the subject to the civilians," said Yang Xudong, a professor in the Department of Building Science at Tsinghua University in Beijing who specializes in indoor air quality and pollution control research. "There's not enough recognition on the subject, and the government's support is essential."

Ezzati said that the solution must involve cooperation from China's powerful economic and energy sectors.

"The nation's public health sector realizes the problem," he said. "But those who can influence a solution and those who care about it happen to be different people."

Chinese officials have recently become more sensitive to the environmental cost of the country's economic boom after a series of high-profile pollution accidents and worldwide reports prior to the recent Summer Olympics games to its deadening air pollution.

Beijing officials announced last week that they will ban half of the city's 3.4 million cars from the roads during periods of very heavy pollution. But on the same day, the state-run press reported that hundreds of villagers had been poisoned by contaminated water in southern China.

Ezzati said China has the resources to make changes.

"In a country managing such fantastic growth, they can do something about this pollution once its gets on their radar screen. The question is whether the government cares about the poorest of the poor as they do in continuing to fuel their economic boom."