Intake fraction of urban wood smoke.

Intake fraction (iF), the proportion of emissions inhaled by an exposed population, is useful for prioritizing sources with the greatest impact on population exposure per unit emissions. This article reports iF estimates for urban winter wood smoke emissions. We used two approaches, incorporating spatiotemporal statistical models for (1) winter wood smoke fine particulate matter (PM2.5) emissions and concentration and (2) concentrations of levoglucosan (a wood smoke particulate marker). Empirical data used in our models were measured in Vancouver, Canada during 2004-2005. We used Monte Carlo simulations to quantify uncertainty. The estimated geometric mean iF (units: per million) is 13 (one geometric standard deviation range: 6.6-24) for wood smoke PM2.5 and 15 (4.5-50) for levoglucosan. These iF estimates are comparable to or slightly larger than iF values for urban vehicle emissions reported in the literature. On average, higher-income areas have lower wood smoke PM2.5 concentrations and intake. Our results emphasize the importance of urban wood smoke as a source of PM2.5 exposure and highlight the comparatively large population exposure and potential environmental justice benefits from reducing wood smoke emissions.