Cozy but deadly

"It's unbelievable what people burn these days," says chimney sweep Alfred Wolf. When Wolf, who is based in the western German city of Aachen, peeks inside the fireplaces and wood-burning stoves of his clients, he finds all sorts of remains of combustible materials that don't belong in there. "There are old shoes, oil-soaked wood, or chopped up clothes cabinets. The fireplaces and stoves end up becoming pollution machines."

The problem is that when such pieces of wood that have been treated with wood preservatives or paint are burned, they emit poisonous dioxins - toxic chemicals that strongly pollute the surrounding air. But that's not all: the chemicals can float down to the ground, penetrate the soil and creep into the food chain.

That's why people should only burn untreated wood in their stoves and fireplaces. In theory, the burning of wood is carbon dioxide neutral. That means that when it is burned, the amount of environmentally-damaging CO2 emissions released equals that which the tree has filtered from the atmosphere during its lifetime. But this environmental equation only works when wood is burned properly.

A clean burn

"Good air circulation in stoves is essential," Wolf says. Older wood-burning stoves often only have one vent. But that's not enough since the oxygen level for complete combustion is limited. Many tiny soot particles - so-called particulate matter - and toxic gases end up being emitted. More modern wood-burning stoves, on the other hand, have several vents and an additional filter function, making them low-polluting.

Burning only dry wood is also essential for clean combustion, as damp wood reduces the burning temperature and facilitates the release of toxic emissions. For this reason, burning wood that has a dampness of more than 25 percent is prohibited in Germany. Still, not everyone heeds these regulations either, Wolf confirms.

Chimneys release over 30,000 tons of particulate matter each year in Germany - about five percent of total particulate matter emissions, which also come from traffic, coal-burning and farming. Unfortunately, the numbers are increasing.

"Particle pollution is harmful," says Barbara Hoffmann of the Leibnitz Research Institute for Environmental Medicine (IUF) in Düsseldorf. The scientist has focused on air pollution and particulate matter research for the past decade.

The size of these fine particles is less than one-hundredth of a millimeter in diameter. That is dramatically smaller than a human hair. "Particulate matter is composed of all sorts of substances," said Hoffmann. "One example is aromatic hydrocarbons which can be carcinogenic in high concentrations."

Particulate matter can enter the human body through the lungs, then reach virtually every part of the body via the blood stream, triggering minor infections. "But these minor infections can lead to negative changes in blood flow," the professor said. "The blood becomes clumpy and a heart attack can result."

Harmful to health

Larger particles are normally filtered by natural barriers, such as nasal mucus. But the smaller the particles, the more easily they can overcome these barriers. Theorectically, that means particulate matter can also reach the brain. Researchers are now discussing whether the risk of Alzheimer's disease can increase as a result.

Numerous scientific studies have clearly linked particle pollution with higher mortality rates and shorter lifespans. Epidemiologist Hoffmann reviews such scientific research on a global scale. "The results of these studies are quite clear, and they are very similar across the continents. There is no doubt in scientific circles."

The European Union has already reacted to concerns about particulate matter by enacting laws to protect health in 2005. Levels of particulate matter cannot exceed more than 50 micrograms per cubic meter per day on more than 35 days a year. Many municipalities have responded to the EU policy by establishing low-emission zones in urban areas and prohibiting vehicles with higher exhaust levels from entering the areas.

But, critics are skeptical about the effectiveness of low-emission zones, and despite cars now on the roads with lower emission rates, many cities are not coming to grips with this particular air pollution problem. Klaus Meiners, from Aachen's Environmental Protection Office, believes the dramatic rise in the number of wood-burning stoves is the culprit. As a result, the city has enacted an air pollution control program, with increased regulations for wood stoves.