Characterization of indoor particulate matter by home heating fuel type in rural New Hampshire homes

Over six million Americans rely on solid fuels for residential heating, which can result in high concentrations of fine and ultrafine particulate matter (PM). Little is known on the characteristics of indoor PM in rural homes, including lung deposited surface area (LDSA) concentration and metals composition, and whether these characteristics may vary by fuel type.

Homes using oil, cordwood, or pellet were recruited into the study. Indoor air quality assessment over 48 hours included PM_2.5 and PM₁₀ mass concentration (Purple Air monitors) and ultrafine (LDSA) PM < 1 μm, number concentration, and diameter (Partector). Teflon© or polytetrafluoroethylene (PTFE) filters were used to collect PM mass for metals characterization by inductively coupled plasma mass spectrometry (ICP-MS). Participants completed a time activity diary to link household behaviors to changes in LDSA, particle number, and size distribution.

Ten homes completed the study- three used primary oil-fueled furnaces/boilers, four used primarily cordwood, and three used pellet fuel. Activity logs and real time measurements highlighted elevated indoor pollution events such as loading wood stoves and cooking. Maximum indoor air particle number concentrations measured were similar across fuel types, though total average particle concentrations, maximum mass, and LDSA concentrations were highly variable. For individual elements Ca, K, Cu, Cd, and Pb, there was a trend of higher concentrations in cordwood heated home, followed by pellet, and then oil heat.

Exposure characteristics and elemental composition of fine and ultrafine particles in rural homes vary by heating fuel type. Due to the contributions from other indoor activities to ultrafine PM, we suggest trace elements might be a better marker of woodsmoke exposure compared to other particle metrics.