Abstract
With an ongoing interest in displacing petroleum-based sources of energy with biofuels, there is a need to measure and model the formation and composition of secondary organic aerosol (SOA) from organic compounds present in biofuels. We performed chamber experiments to study SOA formation from four recently identified biofuel molecules and mixtures and commercial gasoline under high NOx conditions: diisobutylene, cyclopentanone, an alkylfuran mixture, and an ethanol-to-hydrocarbon (ETH) mixture. Cyclopentanone and diisobutylene had a significantly lower potential to form SOA compared to commercial gasoline, with SOA mass yields lower than or equal to 0.2%. The alkylfuran mixture had an SOA mass yield (1.6%) roughly equal to that of gasoline (2.0%) but ETH had an average SOA mass yield (11.5%) that was six times higher than that of gasoline. We used a state-of-the-science model to parameterize or simulate the SOA formation in the chamber experiments while accounting for the influence of vapor wall losses. Simulations performed with vapor wall losses turned off and at atmospherically relevant conditions showed that the SOA mass yields were higher than those measured in the chamber at the same photochemical exposure and were also higher than those estimated using a volatility basis set that was fit to the chamber data. The modeled SOA mass yields were higher primarily because they were corrected for vapor wall losses to the Teflon® chamber.
Highlights
Volatile organic compounds (VOCs), emitted by anthropogenic and biogenic sources, undergo oxidation in the atmosphere to form secondary organic aerosol (SOA)
The chamber experiments and numerical modeling performed in this work suggested that two of the Co-Optima fuels, namely cyclopentanone and diisobutylene, had a signi cantly lower potential to form SOA when compared to gasoline
ETH, on account of a large aromatic fraction, had a much higher potential to form SOA compared to gasoline
Summary
For reasons ranging from energy independence to environmental sustainability, there is ongoing interest in the production of biofuels from sustainable feedstocks to meet current and future energy demands.[5]. Most SOA model parameterizations have not been corrected for losses of vapors to the walls of the Te on® chamber, which can bias SOA production in chamber experiments.[10,11,12] chamber experiments have historically used high initial VOC and oxidant concentrations to ensure abundant SOA production (>20 mg mÀ3) at levels above instrument detection limits (>1 mg mÀ3) These concentrations are signi cantly elevated compared to those found in the atmosphere, including most urban areas.[13] Direct SOA parameterizations derived under these highly polluted conditions may overestimate SOA production in lower-concentration conditions, and may not re ect the magnitude and properties of SOA formed in the atmosphere.[14,15] Experiments are o en challenging to perform under atmospherically relevant conditions (the experiments in this work were performed at elevated VOC levels). The SOA formation was modeled using a state-of-thescience model that accounted for the in uence of vapor wall losses and allowed us to determine atmospherically relevant SOA mass yields
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