AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Petroleum Fuels and Biofuels: A Comparative Environmental Chamber Study of Nighttime Secondary Organic Aerosol Formation
SHAOKAI GAO, Phillips 66 Research Center
Abstract Number: 11 Working Group: Aerosol Chemistry
Abstract A federal mandate requires that U.S. oil refiners blend biofuel, such as ethanol, into gasoline. Ethanol has long been promoted as a ‘green’ fuel because its combustion tends to produce lower emissions of some regulated pollutants. However, the impact on air quality of a wholesale transition from gasoline to biofuel has been difficult to assess, with different atmospheric chemistry models predicting a variety of consequences.
In this study, to better understand ethanol’s environmental impact, nighttime secondary organic aerosol (SOA) formation behavior from the interaction of petroleum fuels (straight-run gasoline, refinery naphtha) and their ethanol blends with NOX and O3 were investigated in a series of environmental chamber experiments. Effects of relative humidity and seed acidity on SOA formation behaviors were also studied. The experimental results showed that despite its high volatility, ethanol could interact with different fuel components under certain circumstances, contributing significantly to nighttime SOA formation. It was found that higher seed acidity could promote SOA formation while higher relative humidity could suppress SOA formation. It was proposed that in addition to oxidation reaction, small molecules such as ethanol could also go through other reaction pathways such as hydration, oligomerization etc. under acidic conditions forming low volatility products, which could further lead to SOA formation. This was confirmed by the lower f44 of the SOA formed from ethanol blends under acidic conditions.
Considering recent experimental results which showed increased emissions of aldehyde compounds (strong precursor for O3 formation) from tailpipe for higher ethanol blends, it is recommended that the environmental impacts of ethanol be evaluated in greater detail.