Kitchen smoke has become a major source of indoor pollution in rural areas and threatens the health of 900 million farmers, experts warned.

Song Guangsheng, director of the China Indoor Environment Test Center, said many rural households were still burning stalks, wood and low-quality coal with high sulfur contents.

"Unscientifically-designed cooking utensils used by farmers often cause incomplete combustion of these fuels, which can generate dense smoke and heavily pollute indoor air if there is no ventilation system," Song said.

According to Song, cooking fumes contain many toxic gases including nitrogen dioxide, sulfur dioxide, carbon monoxide and some cancer-leading pollutants.

An official with the State Environmental Protection Administration (SEPA) pointed out that kitchen smoke was composed of numerous tiny particles that can enter the bloodstream or lungs via the respiratory system. It may lead to pulmonary and respiratory diseases.

"At dusk or on foggy days, temperatures near the ground are usually lower than in rural areas. It will worsen the pollution as it hinders the diffusion of kitchen smoke," the official said.

The World Health Organization and the United Nations Development Program noted that thick acrid smoke from stoves and fires inside homes is associated with approximately 1.6 million deaths per year in developing countries.

Song cited a 1995 report by the World Bank, which said more than 100,000 people in the country die from indoor air pollution each year.

"A considerable proportion of them are rural residents," Song said.

Experts also said that environmental protection efforts in rural areas now mainly target pollution from pesticides and fertilizers, animal waste, water pollution and factory discharges. But little emphasis has been placed on cooking smoke.

Song suggested related departments help rural residents improve their stoves and build exhaust systems to ensure sound indoor ventilation.

He also considered it important to develop clean and renewable energy sources, such as marsh gas, solar energy, wind, hydropower and other environment-friendly energies.

Since 2000, the central government has begun a trial project to help rural residents build marsh gas pits and rebuild toilets, sties and stoves.

In 2003 and this year, the Ministry of Finance allocated 1 billion yuan (US$120.82 million) in national bonds each year to support the building of household-use methane-generating pits.

According to an ambitious plan for methane use, more than 20 million such pits will be built in rural areas by the end of this year. The figure is expected to reach 50 million by 2010. By then, 200 million rural residents will benefit from methane use.