This NCST graduate fellowship award allowed Patrick Roth to focus on and complete multiple projects that will be included in his PhD thesis. Patrick has dedicated his thesis work to understanding the secondary pollutants that form when vehicle exhaust react with atmospheric oxidants. Patrick and his colleagues investigated these reactions utilizing the exhaust from new technology gasoline direct injection (GDI) vehicles operating on a chassis dynamometer in UC Riverside’s Vehicle Emissions Laboratory. While the GDI vehicles are being driven on a consistent driving cycle, they collect and classify the vehicle exhaust. Simultaneously, they inject the vehicle exhaust into UCR’s Mobile Atmospheric Chamber (MACh).
Tailpipe exhaust includes pollutants like Particulate Matter (PM), and various gas phase pollutants (NOx, CO2, CO, and Volatile Organic Compounds). The gas phase pollutants when exposed to high energy UV light emitted from the sun, will react and form heavier, lower volatility products that will begin transitioning onto existing PM. This increase in atmospheric aerosol mass (secondary aerosol) is what the team are most interested in when studying these vehicles. They were able to simulate these reactions in the lab by collecting the exhaust into MACh, and turning on UV lamps. The lamps allow them to control the intensity and duration of the UV irradiation which allows them to get repeatability between tests.
With this NCST award, Patrick investigated how the addition of a gasoline particulate filter (GPF) would affect the secondary pollutants. This study included two new GDI vehicles. Each vehicle was tested over a cold start LA-92 driving cycle. The emissions were collected and subsequently photochemically aged. After the stock configuration of the vehicles were studied, a catalyzed GPF was installed in line with the vehicle exhaust. The vehicles were once again tested over a cold start LA-92 driving cycle and the results were compared. It was found that there was over a 90% reduction in the PM directly from the tailpipe while also reducing the SOA by 40-50%. This finding will help modelers and regulators understand the positive impacts that can occur if catalyzed GPFs are installed on these newer technology GDI vehicles.
Two other projects that Patrick was able to complete while supported by the NCST award focused on the effects of fuel on the secondary aerosol formation. One project focused ethanol content in the fuels (4 fuels, 10%- 78% ethanol). The second study focused more on aromatic content in fuel, but also included varying ethanol (8 fuels 0% to 20% ethanol). Both studies utilized the same driving cycle and conditions to the GPF study. In both experiments, the secondary aerosol formation followed the strongest trend with aromatic content. When the aromatic content of the fuel increased, the SOA formation also increased. The inverse was true, for ethanol content. The work from these studies will provide regulators with information on how altering the fuel properties can affect the tailpipe and secondary emissions from vehicle exhaust.