Four years after the changeout of 1,200 uncertified wood stoves in Libby, Montana, the definitive air quality study has been released. Not surprisingly, it found that changing out stoves improved air quality and children’s health. But some findings were surprising. For one, indoor air quality did not always improve; in fact, it got worse in some homes. Another interesting find was that no health differences could be found in kids from homes with wood stoves compared to those without them. Overall, the air quality benefits were not as great as expected. The detailed report was published along with a thorough critique of the report by health experts pointing toward what future studies should also consider.
* Air emission standards in the United States typically regulate the specific type of device, the fuels, and heat outputs. A recent report indicated that this may allow gaps and variation in coverage, and some residential and small-to-medium–sized biomass units may not be subject to environmental regulations (Handley et al. 2009). In contrast, regulations in Europe are issued according to heat output and type of feeding device (manual or automatic), which provides 100% coverage. More importantly, European PM2.5 standards for wood-burning appliances are significantly lower at about 0.02 to 0.05 lb/million BTU heat output compared with state regulations in the United States at, for example, 0.1 lb/million BTU in Massachusetts and 0.6 lb/million BTU in New York State (Handley et al. 2009). This indicates that in the United States there is room for improvement in terms of reducing emissions from wood-burning appliances. (p. 40)
* It is not clear whether the total number of wood stoves in the community increased in the meantime, because more people may have chosen wood as a cheaper fuel, because of an increasing population size, or both. (p.43)
* In addition, there may be other sources of PM2.5 in the area, such as wood- or coal-burning fireplaces and boilers that were not covered by the changeout program. New York State has noted a tripling in the sales of outdoor wood boilers since the early 1990s (p. 44)
* The wood stove changeout program should be considered a success because 95% of older, high-polluting wood stoves in Libby, Montana, were replaced with more efficient certified wood stoves or with heating systems that did not burn wood. .. However, the air quality improvement was not as large as might have been expected based on the dominant contribution of wood burning to ambient PM2.5 concentrations in the area and the approximately 50% expected reduction in emissions anticipated from each certified stove compared with uncertified models. (p. 45)