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Abstract:
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Transportation fleet emissions have a dominant role in air quality because of their significant contribution to ozone precursor and greenhouse gas emissions . Regulatory policies have emphasized improvements in vehicle fuel economy , alternative fuel use , and engine and vehicle technologies as approaches for obtaining transportation systems that support sustainable development . This study examined the air quality impacts of the partial electrification of the transportation fleet and the use of biofuels for the Austin Metropolitan Statistical Area under a 2030 vision of regional population growth and urban development using the Comprehensive Air Quality Model with extensions (CAMx ) . Different strategies were considered including the use of Plug -in Hybrid Electric Vehicles (PHEVs ) with nighttime charging using excess capacity from electricity generation units and the replacement of conventional petroleum fuels with different percentages of the biofuels E85 and B100 along or in combination . Comparisons between a 2030 regional vision of growth assuming a continuation of current development trends (denoted as Envision Central Texas A or ECT A ) in the Austin MSA and the electrification and biofuels scenarios were evaluated using different metrics , including changes in daily maximum 1 -hour and 8 -hour ozone concentrations , total area , time integrated area and total daily population exposure exceeding different 1 -hour ozone concentration thresholds . Changes in ozone precursor emissions and predicted carbon monoxide and aldehyde concentrations were also determined for each scenario .
Maximum changes in hourly ozone concentration from the use of PHEVs ranged from -8 .5 to 2 .2 ppb relative to ECT A . Replacement of petroleum based fuels with E85 had a lesser effect than PHEVs on maximum daily ozone concentrations . The maximum reduction due to replacement of 100 % of gasoline fuel in light and heavy duty gasoline vehicles by E85 ranged from -2 .1 to 2 .8 ppb . The magnitude of the effect was sensitive to the biofuel penetration level .
Unlike E85 , B100 negatively impacted hourly ozone concentrations relative to the 2030 ECT A case . As the replacement level of petroleum -diesel fuel with B100 in diesel vehicles increased , hourly ozone concentrations increased as well . However , changes due to the penetration of B100 were relatively smaller than those due to E85 since the gasoline fraction of the fleet is larger than the diesel fraction . Because of the reductions in NOx emissions associated with E85 , the results for the biofuels combination scenario were similar to those for the E85 scenario .
Also , the results showed that as the threshold ozone concentration increased , so too did the percentage reductions in total daily population exposure for the PHEV , E85 , and biofuel combination scenarios relative to ECT A . The greatest reductions in population exposure under higher threshold ozone concentrations were achieved with the E85 100 % and 17 % PHEV with EGU controls scenarios , while the B100 scenarios resulted in greater population exposure under higher threshold ozone concentrations . |