Implementation of the Reactive Organic Carbon Framework for U.S. Mobile Source Emissions

BENJAMIN MURPHY, Darrell Sonntag, Karl Seltzer, Havala Pye, Claudia Toro, Evan Murray, U.S. EPA

     Abstract Number: 290
     Working Group: Carbonaceous Aerosol

Abstract
Primary particle emissions are conventionally treated as nonvolatile and inert in mobile-source emission models and subsequently in national scale inventories. However, there is clear scientific evidence that the organic component of particle emissions is semivolatile and that primary vapors span a wide range of volatility, with the lower volatility vapors contributing efficiently to formation of SOA (secondary organic aerosol). To account for these complexities, emissions data must be carefully revised with the most recent scientific findings, while ensuring compatibility with existing assumptions. This presentation will discuss the methodology with which we have revised the PM and VOC speciation used by the Motor Vehicle Emission Simulator (MOVES), maintained by the US EPA, and will report the expected impacts on mobile-source emissions for a recent year (2016).

Previous studies have successfully introduced semivolatile POA and intermediate volatility organic compounds (IVOCs) using top-down assumptions for all anthropogenic emissions, the entire mobile sector, or large subsets of the mobile sector (e.g. gasoline vs. diesel vehicles). This effort implements detailed speciation of PM and VOC, including volatility resolution, directly to the detailed emission model output, thus producing the first such dataset for U.S. mobile-source emissions. Twenty-three VOC and fifteen PM profiles have been updated. We will discuss issues related to translating emissions testing results to model-ready inputs including accounting for missing partitioning of POA, interpretation of filter artifacts and ensuring total reactive organic carbon closure. We also report on changes to predictions of hazardous air pollutant emissions from the mobile sector as a result of updates to the VOC speciation.