▪ Abstract Ethanol is a high performance fuel in internal combustion engines. It is a liquid, which is advantageous in terms of storage, delivery, and infrastructural compatability. Ethanol burns relatively cleanly, especially as the amount of gasoline with which it is blended decreases. Evaporative and toxicity-weighted air toxics emissions are consistently lower for ethanol than for gasoline. It is likely that vehicles can be configured so that exhaust emissions of priority pollutants are very low for ethanol-burning engines, although the same can probably be said for most other fuels under consideration. Recent work suggests that ethanol may be more compatible with fuel cell—powered vehicles than has generally been assumed. Research and development—driven advances have clear potential to lower the price of cellulosic ethanol to a level competitive with bulk fuels. Process areas with particular potential for large cost reductions include biological processing (with consolidated bioprocessing particularl...

OVERVIEW AND EVALUATION OF FUEL ETHANOL FROM CELLULOSIC BIOMASS: Technology, Economics, the Environment, and Policy

Light-duty vehicle emissions were measured at the Caldecott Tunnel in August and October 1994. In the interval between these two periods, the average oxygen content of gasoline sold in the San Francisco Bay area increased from 0.3 to 2.0% by weight. Compared to the August (low-oxygenate) sampling period, measured pollutant emission rates during the October (high-oxygenate) sampling period for CO and VOC decreased by 21 +/- 7 and 18 +/- 10%, respectively, while NOx emissions showed no significant change. Formaldehyde emissions increased by 13 +/- 6%, acetaldehyde emissions did not change significantly, and benzene emissions decreased by 25 +/- 17%. Speciated VOC emission profiles show that the use of oxygenated gasoline resulted in higher MTBE and lower aromatic hydrocarbon emissions, higher isobutene, and lower aromatic aldehydes. The normalized reactivity of NMOG emissions did not change significantly between the low-oxygenate and high-oxygenate sampling periods. VOC exhaust speciation profiles for vehicles operating in the hot-stabilized mode at the Caldecott Tunnel math the speciation profile for cold-start emissions from new vehicles as measured in the Auto/Oil program. California's motor vehicle emission factor model, EMFAC7F, accurately predicts the VOC/NOx ratio measured at the Caldecott Tunnel in August, but underpredicts the observed CO/NOx ratio by a factor of 1.5-2.2 over the range of vehicle speeds observed at the tunnel.

Impacts of Oxygenated Gasoline Use on California Light-Duty Vehicle Emissions

We reviewed toxicological studies, both experimental and epidemiological, that appeared in international literature in the period 1990-1997 and included both leaded and unleaded gasolines as well as their components and additives. The aim of this overview was to select, arrange, and present references of scientific papers published during the period under consideration and to summarize the data in order to give a comprehensive picture of the results of toxicological studies performed in laboratory animals (including carcinogenic, teratogenic, or embryotoxic activity), mutagenicity and genotoxic aspects in mammalian and bacterial systems, and epidemiological results obtained in humans in relation to gasoline exposure. This paper draws attention to the inherent difficulties in assessing with precision any potential adverse effects on health, that is, the risk of possible damage to man and his environment from gasoline. The difficulty of risk assessment still exists despite the fact that the studies examined are definitely more technically valid than those of earlier years. The uncertainty in overall risk determination from gasoline exposure also derives from the conflicting results of different studies, from the lack of a correct scientific approach in some studies, from the variable characteristics of the different gasoline mixtures, and from the difficulties of correctly handling potentially confounding variables related to lifestyle (e.g., cigarette smoking, drug use) or to preexisting pathological conditions. In this respect, this paper highlights the need for accurately assessing the conclusive explanations reported in scientific papers so as to avoid the spread of inaccurate or misleading information on gasoline toxicity in nonscientific papers and in mass-media messages.

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Potential health effects of gasoline and its constituents: A review of current literature (1990-1997) on toxicological data.

The wide-scale use of methyl tertiary butyl ether (MTBE) in gasoline has resulted in substantial public controversy and action to ban or control its use due to perceived impacts on water quality. Because oxygenates are still required under federal law, considerable research has focused on ethanol as a substitute for MTBE. In this article, we summarize the currently available literature on the air and water quality risks and benefits of MTBE versus ethanol as alternative fuel oxygenates. We find that MTBE-fuel blends are likely to have substantial air quality benefits; ethanol-fuel blends appear to offer similar benefits, but these may be at least partially negated because of ethanol's propensity to increase emissions and ambient concentrations of some air contaminants. Releases of gasoline containing either MTBE or ethanol could have an impact on some drinking water sources, although the impacts associated with MTBE tend to relate to aesthetics (i.e., taste and odor), whereas the impacts associated with ethanol generally relate to health risk (i.e., greater exposure to gasoline constituents such as benzene). It is likely that these water quality impacts will be outweighed by the air quality benefits associated with MTBE and perhaps ethanol use, which affect a much larger population. A lack of data on environmental exposures and associated health impacts hinders the completion of a comprehensive quantitative risk-benefit analysis, and the available air and water quality data should be evaluated in a broader risk-management context, which considers the potential life-cycle impacts, costs, and feasibility associated with alternative fuel oxygenates.

Data available for evaluating the risks and benefits of MTBE and ethanol as alternative fuel oxygenates.

This paper examines closely and compares the potential hazards of inhalation of two types of gasoline (car fuel). The first type is the commonly use leaded gasoline and the second is the unleaded type enriched with oxygenate additives as lead substituent in order to raise the octane number. The impacts of gasoline exposure on Na+, K+-ATPase, superoxide dismutase (SOD), acetylcholinesterase (AChE), total protein, reduced glutathione (GSH), and lipid peroxidation (TBARS) in the cerebral cortex, and monoamine neurotransmitters dopamine (DA), norepinephrine (NE) and serotonin (5-HT) in the cerebral cortex, hippocampus, cerebellum and hypothalamus were evaluated. The effect of gasoline exposure on the aggressive behaviour tests was also studied. The present results revealed that gasoline inhalation induced significant fluctuations in the levels of the monoamine neurotransmitters in the studied brain regions. This was concomitant with a decrease in Na+, K+-ATPase activity and total protein content. Moreover, the group exposed to the unleaded gasoline exhibited an increase in lipid peroxidation and a decrease in AChE and superoxide dismutase activities. These physiological impairments were accompanied with a higher tendency towards aggressive behaviour as a consequence to gasoline inhalation. It is concluded from the present work that chronic exposure to either the leaded or the unleaded gasoline vapours impaired the levels of monoamine neurotransmitters and other biochemical parameters in different brain areas and modulated several behavioural aspects related to aggression in rats.

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Impact of gasoline inhalation on some neurobehavioural characteristics of male rats

The objective of this project was to investigate the emissions effects of low-oxygenate gasoline blends on exhaust and evaporative emissions from a test fleet of California certified light-duty autos. Thirteen vehicles were procured and tested using four gasoline-oxygenate blends over three test cycles. The four gasoline blends were: Methyl Tertiary Butyl Ether (MTBE), Ethyl Tertiary Butyl Ether (ETBE), and 'match' and 'splash' blends of ethanol (in the 'match' blend the fuel Reid Vapor Pressure (RVP) is held constant, while in the 'splash' blend the fuel RVP is allowed to increase). Hydrocarbon and carbon monoxide exhaust emissions were generally reduced for the oxygenated blends, the exception being the 'splash-blended' ethanol gasoline which showed mixed results. Older technology vehicles (e.g., non-catalyst and oxidation catalyst) showed the greatest emissions reductions regardless of gasoline blend, while later technology vehicles showed the smallest reductions. Evaporative emissions and toxics were generally reduced for ETBE, while results for the other blends were mixed.

T.H. DeFries

Papers

Effect of use of low oxygenate gasoline blends upon emissions from California vehicles. Final report