Organic/elemental carbon and woodsmoke tracer concentrations following a community wide woodstove changeout program

As part of the Libby, Montana community-wide woodstove changeout program conducted between 2005 and 2008, nearly 1200 older model woodstoves were replaced with cleaner burning devices such as EPA-certified stoves. The reduction in overall ambient wintertime PM_2.5 mass has been documented. However, much less is known about the changes in the chemical (specifically the organic) makeup of the ambient particles as the emission sources changed within the community with the implementation of the cleaner-burning home heating devices.Overall, PM_2.5 mass levels decreased by 25%, while Total Carbon (TC) showed a 26% reduction when comparing the pre- and post-changeout concentrations. As the TC fraction is heavily influenced by Organic Carbon (OC) in Libby, trends were similar. Differential effects were observed for OC fractions according to analytical temperatures. Concentrations of Elemental Carbon (EC) were fairly consistent throughout the changeout, and did not show a dramatic reduction similar to the measured OC. Results from the polar organic compound program showed that the majority of the secondary aerosols were reduced, as were the majority of the woodsmoke markers such as levoglucosan and several methoxyphenols. However, the concentrations of resin acids actually increased following the woodstove changeout, suggesting that the chemistry of the particles have been altered as a result of this community-wide intervention.