"Black carbon" from wood burning chokes Chilean towns.

On winter nights. Carmen Ahumada is unable to see across the street to her neighbor's house. Visibility in Temuco, Chile, can be as little as five meters, she said.

Temuco, with a population of 300,000, has the fourth most-polluted air in the country, according to local media. The burning of firewood for heating, cooking, and other uses is the main source of soot particulates, known as "black carbon," that enter the air at more than four times the World Health Organization's recommended limit.

On many counts, Chile has taken the lead in Latin America in tackling urban air pollution. But little has been done to help smaller towns address particulate pollution from wood burning, which supplies 20 percent of the country's energy, according to local residents and officials.

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Burning does not completely break down the wood, resulting in the release of particulate matter and carbon monoxide into the environment. The soot contains heavy metals, benzene, formaldehyde, and carcinogenic dioxins. Documented health effects, especially among the elderly and young children, include asthma, respiratory infections, cardiovascular disease, and cataracts.

The Intergovernmental Panel on Climate Change concluded in its 2007 assessment that burning firewood may affect the global climate as well. When soot settles on light-colored snow or ice, it reduces the capacity of these surfaces to reflect sunlight and contributes to atmospheric warming. "It doesn't matter if it's a fossil fuel or a biomass fuel, it all contributes to the problem," said Kirk Smith, a global environmental health professor at the University of California at Berkeley.

In Temuco, where 85 percent of residents burn firewood, the government began measuring local air pollution levels in 2002. Apart from municipal efforts to promote more sustainable burning methods, no official policies regulate firewood use. "Firewood actually isn't recognized as a fuel [by the government]," said Rony Pantoja, a technical secretary for Chile's National Firewood Certification System, a partnership between firewood dealers and the government. "There are no policies that modernize and make sustainable [firewood] use."