Abstract A major anthropogenic source of atmospheric particulate matter (PM) is the transportation sector, specifically motor vehicles. There is a substantial potential to significantly reduce ambient PM levels through the development of better fuels. The Department of Energy’s Co-Optima initiative is aimed at developing more sustainable, scalable, and tailpipe-emission friendly fuels. This initiative would reduce direct tailpipe emissions of carbonaceous aerosol (i.e., black carbon and primary organic aerosol) but no consideration is given to the secondary organic aerosol (SOA) formed through the atmospheric oxidation of gas-phase hydrocarbon emissions. Hence, there is a need to quantify the SOA formed from these prospective fuels.
In this work, we performed experiments in a 10 m3 Teflon environmental chamber to measure the formation and composition of SOA from photooxidation of unburned Co-Optima fuels. We tested four of the eight biofuels identified by the Co-Optima initiative as drop-in substitutes for gasoline. The four biofuels were: Vertifuel (complex mixture of hydrocarbons with 70% aromatics), furan mixture (60:40 weight ratio of dimethylfuran and 2-methylfuran), cyclopentanone, and diisobutylene. The photooxidation experiments were initiated using the hydroxyl radical, which was formed through the photolysis of nitrous acid (HONO) and performed under atmospherically-relevant concentrations of NOx. The SOA volume concentration was tracked using a scanning mobility particle sizer and the SOA composition was captured using an aerosol mass spectrometer. Preliminary results suggest that all of the biofuels tested had much higher SOA mass yields compared to unburned gasoline. This implied that blending these biofuels with gasoline might lead to increases in ambient SOA in urban areas where motor vehicles account for a significant fraction of the fine particle pollution.
Ongoing work is focused on performing additional experiments with these biofuels to allow parameterizations to be developed for air quality models and using those parameterizations in air quality models to examine the tradeoffs between lower primary emissions and higher secondary production on ambient SOA mass concentrations.