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Carbonaceous Aerosols Emitted from Light-Duty Vehicles Operating on Gasoline and Ethanol Fuel Blends
Citation:
Hays, M., W. Preston, BJ George, Judy Schmid, R. Baldauf, R. Snow, J. Robinson, T. Long, AND J. Faircloth. Carbonaceous Aerosols Emitted from Light-Duty Vehicles Operating on Gasoline and Ethanol Fuel Blends. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 47(24):14502-14509, (2013).
Impact/Purpose:
In sum, determination of the environmental and public health impacts due to increased renewable fuel use is necessary. Where, when, and what LDV emissions are released to the atmosphere is key to understanding how transportation influences air quality and public health. This study produced emissions data specific to LDV operations typical of different driving rates, ambient conditions, and fuel technologies. The possible shift from lower to higher EC emissions fractions due to capturing more realistic driving scenarios will have to be monitored closely, considering that EC is surrogate for BC, a pollutant with multiple direct and indirect climate forcing roles. The reduction in lighter PAH emissions coupled with the limited change in heavier PAH observed here with e85 use is noted as a putative toxicological concern. As discussed, these type compositional changes may also influence the absorptive properties of soot, altering its photooxidation potential in the atmosphere. Individual SVOC emissions from the Tier 2 LDV and modern fuel technologies used in the present study appear to be orders of magnitude lower and distributed differently than those representing the current SPECIATE inventory, which links directly to apportionment, climate, and air quality model predictions. The hope is that this study sheds light on PM compositional changes due to ethanol fuel use in LDVs that can affect the environment. Some of the compositional uncertainties noted when switching from moderate to high ethanol content fuels suggest that bounding emissions from ethanol use in LDVs will continue to be a topic worthy of future scientific inquiry.
Description:
This study examines the chemical properties of carbonaceous aerosols emitted from three light-duty gasoline vehicles (LDVs) operating on gasoline (e0) and ethanol-gasoline fuel blends (e10 and e85). Vehicle road load simulations were performed on a chassis dynamometer using the three-phase LA-92 Unified Driving Cycle (UDC). Effects of LDV operating conditions and ambient temperature (-7 ˚C and 24 ˚C) on particle-phase semivolatile organic compounds (SVOCs) and organic and elemental carbon (OC and EC) emissions were investigated. SVOC concentrations and OC and EC fractions were determined with thermal extraction-gas chromatography-mass spectrometry (TE-GC-MS) and thermal-optical analysis (TOA), respectively. LDV aerosol emissions were predominantly carbonaceous, and EC/PM (w/w) decreased linearly with increasing fuel ethanol content. TE-GC-MS analysis accounted for up to 4% of the fine particle (PM2.5) mass, showing the UDC phase-integrated sum of identified SVOC emissions ranging from 0.703 µg km-1 to 18.8 µg km-1. Generally, higher SVOC emissions were associated with low temperature (-7 ˚C) and engine ignition; mixed regression models suggest these emissions rate differences are significant. Use of e85 significantly reduced the emissions of lower molecular weight PAH. However, a reduction in higher molecular weight PAH entities in PM was not observed. Individual SVOC emissions from the Tier 2 LDVs and fuel technologies tested are substantially lower and distributed differently than those values populating the United States emissions inventories currently. Hence, this study is likely to influence future apportionment, climate, and air quality model predictions that rely on source combustion measurements of SVOCs in PM.
