Impact/Purpose:

The core hypothesis underlying this project is that volatility based representations of primary organic aerosol emissions data will improve predictions of chemical transport models. Specific project objectives include: to investigate methodologies for routine measurement of the volatility distribution of emissions of low-volatility organics from combustion systems; to measure emission factors for, and volatility distributions of, low-volatility organics emitted by on-road and non-road mobile sources; to develop techniques to efficiently update emission inventories for use with the volatility basis set approach using the emissions data collected by this project and other studies; and to conduct chemical transport model simulations with the updated inventories for the Eastern United States and California and to compare model predictions with ambient organic aerosol data.

Description:

Organic material contributes a significant fraction of PM_2.5 mass across all regions of the United States, but state-of-the-art chemical transport models often substantially underpredict measured organic aerosol concentrations. Recent revisions to these models that account for gas-particle partitioning of primary emissions and secondary organic aerosol production from all low-volatility organics improve model performance, but full implementation of these ideas is hampered by critical data gaps. This proposal addresses one of those gaps, namely volatility-based emissions data that are needed to develop inventories for the next generation of chemical transport models.

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The proposed research integrates emissions testing, ambient measurements, a tunnel study, emission inventory development, and regional chemical transport modeling to quantify and fix suspected errors involving the representation of low-volatility organics in existing emission inventories. The plan is to update inventories by representing primary organic aerosol emissions using a volatility distribution and by quantifying the amount of missing intermediate volatility vapors. The source testing will be performed in collaboration with the California Air Resources Board using chassis dynamometers and gasoline, diesel and non-road sources recruited from the in-use fleet.

The source test data will be compared to measurements made in a highway tunnel to assess the applicability of the chassis dynamometer data to in-use vehicle emissions. The experiments will feature advanced instrumentation coupled with dilution sampler and thermodenduer volatility measurements. Gas-chromatography mass-spectrometry of filter and sorbent samples will be used to quantify the emissions of all low volatility organics. The new data will be used to update emission inventories used by chemical transport models. Predictions of these models for the Eastern United States and California will be compared to ambient organic aerosol data to evaluate the impact of the proposed revisions on model performance.

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