Why burning wood and burning fossil fuels produce similar pollutants?

A very simple question sometimes does not lead to a simple answer. But, in general yes, similar in chemical composition, dissimilarities in pollution threat levels. A "pollutant" does harm to natural processes. Both burning of wood and fossil fuels generate carbon dioxide, and excess CO2 in our atmosphere contributes to global warming. See http://en.wikipedia.org/wiki/Wood_fuel Wood burning creates particulate air pollution can contribute to human health problems and increased hospital admissions for asthma & heart diseases. Wood burning smoke pollutants include nitrogen oxide, sulfur dioxide, volatile organics, radioactive compounds, carbon monoxide, formaldehyde and suspect carcinogens (polycyclic aromatics and dioxins), See: http://www.lungusa.org/site/c.dvLUK9O0E/b.23354/k.100/Woodburning.htm According to the American Lung Association, oil or natural gas generate less pollutants in the home per btu, than wood. They also recommend on their website how to make wood burning safer. The fossil fuels are generally considered coal, oil and natural gas. See: http://en.wikipedia.org/wiki/Fossil_fuel The list of pollutants are similar to wood burning, CO2, nitrogen oxide and sulfur dioxide. Harmful volatile organics and radioactive compounds (uranium and thorium) are also produced as with wood burning. The pollution threat can not just be measured in what these energy sources produce, but how much they produce. Again, refer to Wikipedia under fossil fuels, and you will see that a steep increase in released emission of carbon to the atmosphere beginning in 1950 from fossil fuel combustion.