AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Intake Fraction for Urban Emissions of Semivolatile Organic Compounds from Vehicles
JOSHUA APTE, Julian Marshall, William Nazaroff, University of California, Berkeley
Abstract Number: 687 Working Group: Aerosol Exposure
Abstract We model the inhalation intake fraction (iF) for semivolatile organic emissions from urban vehicles. Population exposure to organic vehicle emissions is strongly affected by photochemical oxidation (“aging”), dilution, and other processes that alter gas-particle partitioning. Accordingly, the overall magnitude and spatial distribution of inhalation intake of semivolatile emissions may differ substantially from that of non-reactive emissions. In this investigation, we compare and contrast patterns of iF for semivolatile vehicle emissions with those of primary, conserved (“inert”) pollutants.
We use the volatility basis set framework to account for the dynamic phase partitioning of primary organic emissions owing to dilution and aging. We develop a nested multi-compartment model to simulate exposures at three spatial scales: urban core (length 25 km), periurban (100 km), and regional (400 km). Results are reported separately for particle and vapor-phase exposures as a function of the volatility of emitted material.
For urban emissions of inert pollutants, ~70% of domain-wide population intake occurs in the same compartment as emissions. In contrast, for semivolatile emissions, spatial patterns and gas-particle partitioning of intake depend substantially on emissions volatility. Low volatility organic emissions in urban areas produce predominantly intraurban, particle-phase exposures (similar to inert pollutants). As volatility of material emitted in urban areas increases, three key trends emerge that reduce particle-phase iF: (1) the overall proportion of population exposure that takes place in the particle phase decreases and the proportion of exposure in the gas phase increases, (2) photochemically aged material accounts for a larger fraction of particle-phase population intake, and (3) regional-scale exposures account for the predominant fraction of organic aerosol exposure attributable to urban precursor emissions. Since higher volatility compounds account for a large fraction of motor vehicle emissions, the overall iF for organic particles attributable to urban semivolatile organic emissions is lower than for inert pollutants.