Burn Cycle Emissions from a Wood Burning Stove

Wood-burning stoves are used worldwide to provide heat for home heating and cooking yet the resulting fine particle and gas emissions can adversely affect human health. Wood smoke toxicity results not only from particle exposure but also from carcinogenic organic compounds such as polycyclic aromatic hydrocarbons that are emitted as gases or adsorbed onto the particles. However, it is not well understood how burning conditions affect the types of chemical compounds formed nor is it well characterized which compounds are responsible for adverse human health effects. Emission factors for particles and 16 U.S. Environmental Protection Agency polycyclic aromatic hydrocarbon compounds were determined for oak and pine woods across four burn stages (start, high flame, low flame, and smolder) for a cast iron stove that operated under predominantly forced-draft conditions due to the close coupling of the dilution duct to the stove stack. Sampling was performed in a dilution duct at dilution air-stack gas mass ratios between 10 and 35. Burn stage particulate matter emission factors varied between non-detect and 13.2 g/kg dry fuel, with higher burn rates (initial burn stages) producing significantly greater particle mass per kg wood burned than the lower burn rates (latter burn stages). The average pine particle emission factor was 5.8 g/kg dry fuel (n=6) which was significantly different from oak at 3.2 g/kg dry fuel (n=5) (p=0.0164). The 16 priority polycyclic aromatic hydrocarbons were quantified. Phenanthrene was most common in oak wood smoke at 3.9 mg/kg (n=1) and acenaphthylene and naphthalene were the most common in pine smoke, at 8.0 and 3.9 mg/kg, respectively (n=1, each). This study shows that both the type of fuel burned and the stage of burn within the burn cycle have significant effects on particle emission. Our data suggest that startup emissions are particularly important: particle emissions were 110 percent greater than the average across the entire burn cycle, in the case of oak, and 83 percent greater in the case of pine. The present work increases our understanding of how stove operation and fuel type affect emissions of air pollutants. This work also serves as preliminary characterization of the wood smoke aerosol that will be used in controlled human exposure studies at the University of California, San Francisco.