Response: Open burning of yard waste includes any unenclosed burning of yard waste, which generally includes tree parts, leaves, and other biomass but may also include other household waste as well. Burning yard waste is typically regulated by local authorities. Open burning of yard waste is generally a source of concern due to its high pollutant emissions and to its increased fire and safety risks. Open burning is a substantial source of pollution, especially as compared to other municipal waste combustors or other closed burning, because it does not burn the waste efficiently or completely, as evidenced by the black or grey smoke coming from the open burn. This smoke is black from particles and soot produced by the inefficient burning. Of further concern is that open burns emit pollution at ground level and at specific times of the year. As a result, exposures to open burn-related pollutants may be more intense than would be experienced from other typical air pollutant sources. The type of pollutants emitted from open burn fires into the air depends on the type of waste or trash being burned. In general, however, open burning emits particles that can be inhaled into the lungs (PM10 and PM2.5), toxic chemicals, carbon dioxide (a greenhouse gas), carbon monoxide, nitrogen oxides, and volatile organic compounds. In addition, larger amounts of toxic chemicals, especially dioxins and polycyclic aromatic hydrocarbons (PAHs), will be emitted if the burning includes household garbage. Exposures to each of these pollutants have been shown in many research studies to be dangerous to human health.
Despite this, there is little data on the amount and type of pollution that is emitted from the burning of yard waste. In a study conducted in Oregon (Edgerton et al., JAPCA, 1984), open burning of twigs, branches, leaves, and other domestic yard debris was shown to be a major source of PM2.5 during the spring, with contributions surprisingly similar to those for wood-burning stoves in the winter. For example, open burning contributed about 60 ug/m3 to PM2.5 levels in the spring, which was about 20% higher than the amount contributed by wood-burning stoves in the winter. More recently, a review of air toxic emissions from various types of open burning was published by Lemieux et al. (Progress in Energy and Combustion Science, 2003). The authors could find little data on yard waste burning, but did find several studies that showed that PAHs and semivolatile organic compounds (SVOCs) were emitted from yard waste burning, with the specific PAHs and SVOCs dependent on the type of tree burned. Clearly, more work is needed in this area.
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Helen Suh MacIntosh is a professor in environmental health at Harvard University and studies how pollution behaves in the environment and how it affects people's health. Please keep in mind that her answers are just her interpretation of available information and should not be taken as the only viewpoint or solution to a problem. Use this column at your own risk. Having said this, please feel free to post any of your environmental health questions to Helen@TreeHugger.com.