AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Inhalation Intake Fractions of Vehicle-Attributable Organic PM2.5
JOSHUA APTE, Julian Marshall, William Nazaroff, University of California, Berkeley
Abstract Number: 617 Working Group: Aerosol Exposure
Abstract Fine particulate matter (PM$_(2.5)) attributable to light-duty vehicles is substantially comprised of semivolatile organic material. The composition and phase partitioning of primary organic aerosol (POA) is understood to be influenced by background organic aerosol (OA) concentrations and evolve in response to changing temperature, dilution processes, and photochemical aging. Although such dynamic processes may substantially influence population exposure to vehicle-emitted PM$_(2.5), these phenomena are typically not incorporated into source-oriented exposure models. Here, we present preliminary estimates of the intake fraction (iF) of OA attributable to emissions from urban vehicles.
To make the assessment, we employ a novel fate and transport model to characterize population exposure to vehicle-attributable OA. Dynamic phase partitioning of primary organic emissions owing to dilution and aging is simulated using a volatility basis set (VBS) framework. Exposures are evaluated at multiple spatial scales: in the on-road microenvironment, at urban-ambient conditions, and at the regional scale. The contribution to overall intake is estimated for each microenvironment and summed to determine the total intake fraction of vehicle-attributable OA. Likewise, iF is estimated separately for OA exposures attributable to gas- and particle-phase primary emissions.
Owing to dilution-induced shifts in gas-particle partitioning, the intake fraction for POA may be substantially lower than for vehicle emissions of conserved pollutants. Preliminary results suggest that most population intake of vehicle-attributable OA takes place at the urban scale, with smaller contributions from on-road and regional-scale exposures. Interestingly, regional-scale photochemistry produces large quantities of oxidized POA on a mass basis, but may result in only modest population exposures, since production is spatially dispersed and has relatively low proximity to populations. A consequence of these results is that population intake of vehicle-attributable PM$_(2.5) may be more strongly influenced by primary species than would be indicated by regional-scale models or measurements.