Natural and anthropogenic ethanol sources in north america and potential atmospheric impacts of ethanol fuel use

We used an ensemble of aircraft measurements with the GEOS-Chem chemical transport model to constrain present-day North American ethanol sources, and gauge potential long-range impacts of increased ethanol fuel use. We find that current ethanol emissions are underestimated by 50% in Western North America, and overestimated by a factor of 2 in the east. Our best estimate for year-2005 North American ethanol emissions is 670 GgC/y, with 440 GgC/y from the continental U.S. We apply these optimized source estimates to investigate two scenarios for increased ethanol fuel use in the U.S.: one that assumes a complete transition from gasoline to E85 fuel, and one tied to the biofuel requirements of the U.S. Energy Indepence and Security Act (EISA). For both scenarios, increased ethanol emissions lead to higher atmospheric acetaldehyde concentrations (by up to 14% during winter for the All-E85 scenario and 2% for the EISA scenario) and an associated shift in reactive nitrogen partitioning reflected by an increase in the peroxyacetyl nitrate (PAN) to NO(y) ratio. The largest relative impacts occur during fall, winter, and spring because of large natural emissions of ethanol and other organic compounds during summer. Projected changes in atmospheric PAN reflect a balance between an increased supply of peroxyacetyl radicals from acetaldehyde oxidation, and the lower NO(x) emissions for E85 relative to gasoline vehicles. The net effect is a general PAN increase in fall through spring, and a weak decrease over the U.S. Southeast and the Atlantic Ocean during summer. Predicted NO(x) concentrations decrease in surface air over North America (by as much 5% in the All-E85 scenario). Downwind of North America this effect is counteracted by higher NO(x) export efficiency driven by increased PAN production and transport. From the point of view of NO(x) export from North America, the increased PAN formation associated with E85 fuel use thus acts to offset the associated lower NO(x) emissions.     

Carbonyl and nitrogen dioxide emissions from gasoline- and diesel-powered motor vehicles

Carbonyls can be toxic and highly reactive in the atmosphere. To quantify trends in carbonyl emissions from light-duty (LD) vehicles, measurements were made in a San Francisco Bay area highwaytunnel bore containing essentially all LD vehicles during the summers of 1999, 2001, and 2006. The LD vehicle emission factor for formaldehyde, the most abundant carbonyl, did not change between 1999 and 2001, then decreased by 61 +/- 7% between 2001 and 2006. This reduction was due to fleet turnover and the removal of MTBE from gasoline. Acetaldehyde emissions decreased by 19 +/- 2% between 1999 and 2001 and by the same amount between 2001 and 2006. Absent the increased use of ethanol in gasoline after 2003, acetaldehyde emissions would have further decreased by 2006. Carbonyl emission factors for medium- (MD) and heavy-duty (HD) diesel trucks were measured in 2006 in a separate mixed-traffic bore of the tunnel. Emission factors for diesel trucks were higher than those for LD vehicles for all reported carbonyls. Diesel engine exhaust dominates over gasoline engines as a direct source of carbonyl emissions in California. Carbonyl concentrations were also measured in liquid-gasoline samples and were found to be low (< 20 ppm). The gasoline brands that contained ethanol showed higher concentrations of acetaldehyde in unburned fuel versus gasoline that was formulated without ethanol. Measurements of NO2 showed a yearly rate of decrease for LD vehicle emissions similar to that of total NOx in this study. The observed NO2/NOx ratio was 1.2 +/- 0.3% and 3.7 +/- 0.3% for LD vehicles and diesel trucks, respectively.     

A decade of on-road emissions measurements

A multiyear, on-road emission measurement program carried out in the cities of Chicago, Illinois; Denver, Colorado; Los Angeles (LA), California; and Phoenix, Arizona shows large, fuel-specific tailpipe emissions reductions at all of the sites for carbon monoxide (CO), hydrocarbons (HC), and nitric oxide (NO). CO emissions decreased between 56% (Denver) and 71% (Chicago), HC emissions decrease between 27% (Phoenix) and 63% (Denver), and NO emissions have dropped between 48% (West LA) and 68% (Chicago). Three observed factors common to all of the sites are that the emission reductions are occurring in vehicles of all ages, that the influence of engine load on fuel-specific emissions, especially for CO and NO, is reduced and that fleet-averaged emission deterioration is near zero for model years newer than 2001 and older than 1990. These nationwide data sets imply that the majority of these on-road emissions reductions are the result of continued improvements in function and durability of vehicle emission control systems and that inspection and maintenance and fuel reformulation programs have only played a minor role.     

Emissions of aldehydes and ketones from a two-stroke engine using ethanol and ethanol-blended gasoline as fuel

Besides aliphatic gasoline, ethanol-blended gasoline intended for use in small utility engines was recently introduced on the Swedish market. For small utility engines, little data is available showing the effects of these fuels on exhaust emissions, especially concerning aldehydes and ketones (carbonyls). The objective of the present investigation was to study carbonyl emissions and regulated emissions from a two-stroke chain saw engine using ethanol, gasoline, and ethanol-blended gasoline as fuel (0%, 15%, 50%, 85%, and 100% ethanol). The effects of the ethanol-blending level and mechanical changes of the relative air/fuel ratio, lambda, on exhaust emissions was investigated, both for aliphatic and regular gasoline. Formaldehyde, acetaldehyde, and aromatic aldehydes were the most abundant carbonyls in the exhaust. Acetaldehyde dominated for all ethanol-blended fuels (1.2-12 g/kWh, depending on the fuel and lambda), and formaldehyde dominated for gasoline (0.74-2.3 g/kWh, depending on the type of gasoline and lambda). The main effects of ethanol blending were increased acetaldehyde emissions (30-44 times for pure ethanol), reduced emissions of all other carbonyls exceptformaldehyde and acrolein (which showed a more complex relation to the ethanol content), reduced carbon monoxide (CO) and ntirogen oxide (NO) emissions, and increased hydrocarbon (HC) and nitrogen dixodie (NO2) emissions. The main effects of increasing lambda were increased emissions of carbonyls and nitrogen oxides (NOx) and reduced CO and HC emissions. When the two types of gasoline are considered, benzaldehyde and tolualdehyde could be directly related to the gasoline content of aromatics or olefins, but also acrolein, propanal, crotonaldehyde, and methyl ethyl ketone mainly originated from aromatics or olefins, while the main source for formaldehyde, acetaldehyde, acetone, methacrolein, and butanal was saturated aliphatic hydrocarbons.     

Environmental implications of municipal solid waste-derived ethanol

We model a municipal solid waste (MSW)-to-ethanol facility that employs dilute acid hydrolysis and gravity pressure vessel technology and estimate life cycle energy use and air emissions. We compare our results, assuming the ethanol is utilized as E85 (blended with 15% gasoline) in a light-duty vehicle, with extant life cycle assessments of gasoline, corn-ethanol, and energy crop-cellulosic-ethanol fueled vehicles. We also compare MSW-ethanol production, as a waste management alternative, with landfilling with gas recovery options. We find that the life cycle total energy use per vehicle mile traveled for MSW-ethanol is less than that of corn-ethanol and cellulosic-ethanol; and energy use from petroleum sources for MSW-ethanol is lower than for the other fuels. MSW-ethanol use in vehicles reduces net greenhouse gas (GHG) emissions by 65% compared to gasoline, and by 58% when compared to corn-ethanol. Relative GHG performance with respect to cellulosic ethanol depends on whether MSW classification is included or not. Converting MSW to ethanol will result in net fossil energy savings of 397-1830 MJ/MT MSW compared to net fossil energy consumption of 177-577 MJ/MT MSW for landfilling. However, landfilling with LFG recovery either for flaring or for electricity production results in greater reductions in GHG emissions compared to MSW-to-ethanol conversion.     

Replacing gasoline with corn ethanol results in significant environmental problem-shifting

Previous studies on the life-cycle environmental impacts of corn ethanol and gasoline focused almost exclusively on energy balance and greenhouse gas (GHG) emissions and largely overlooked the influence of regional differences in agricultural practices. This study compares the environmental impact of gasoline and E85 taking into consideration 12 different environmental impacts and regional differences among 19 corn-growing states. Results show that E85 does not outperform gasoline when a wide spectrum of impacts is considered. If the impacts are aggregated using weights developed by the National Institute of Standards and Technology (NIST), overall, E85 generates approximately 6% to 108% (23% on average) greater impact compared with gasoline, depending on where corn is produced, primarily because corn production induces significant eutrophication impacts and requires intensive irrigation. If GHG emissions from the indirect land use changes are considered, the differences increase to between 16% and 118% (33% on average). Our study indicates that replacing gasoline with corn ethanol may only result in shifting the net environmental impacts primarily toward increased eutrophication and greater water scarcity. These results suggest that the environmental criteria used in the Energy Independence and Security Act (EISA) be re-evaluated to include additional categories of environmental impact beyond GHG emissions.     

Life cycle assessment of switchgrass- and corn stover-derived ethanol-fueled automobiles

Utilizing domestically produced cellulose-derived ethanol for the light-duty vehicle fleet can potentially improve the environmental performance and sustainability of the transport and energy sectors of the economy. A life cycle assessment model was developed to examine environmental implications of the production and use of ethanol in automobiles in Ontario, Canada. The results were compared to those of low-sulfur reformulated gasoline (RFG) in a functionally equivalent automobile. Two time frames were evaluated, one near-term (2010), which examines converting a dedicated energy crop (switchgrass) and an agricultural residue (corn stover) to ethanol; and one midterm (2020), which assumes technological improvements in the switchgrass-derived ethanol life cycle. Near-term results show that, compared to a RFG automobile, life cycle greenhouse gas (GHG) emissions are 57% lower for an E85-fueled automobile derived from switchgrass and 65% lower for ethanol from corn stover, on a grams of CO2 equivalent per kilometer basis. Corn stover ethanol exhibits slightly lower life cycle GHG emissions, primarily due to sharing emissions with grain production. Through projected improvements in crop and ethanol yields, results for the mid-term scenario show that GHG emissions could be 25-35% lower than those in 2010 and that, even with anticipated improvements in RFG automobiles, E85 automobiles could still achieve up to 70% lower GHG emissions across the life cycle.     

A systems evaluation on the effectiveness of a catalyst retrofit program in China

A low-cost, rare-earth oxide (REO) catalyst has been recommended as part of China's retrofit program for Chinese carbureted vehicles. This study evaluated: (1) the emission reduction efficiency of the REO catalyst during chassis dynamometer testing on the FTP cycle; (2) the effect that fuel properties had on tailpipe emissions and catalyst efficiency; (3) the importance of vehicle premaintenance as part of a retrofit protocol; and (4) the emission reductions obtained following implementation of the program. Results also show that current in-use Chinese noncatalyst, carbureted vehicles operate excessively rich, resulting in extremely high emissions of CO, gaseous toxic compounds, and other non-methane hydrocarbon species (NMHC). Preretrofit maintenance alone has the potential to reduce these emissions by approximately 50%. Dynamometer emission tests showed emissions reductions of >95% for hydrocarbons, CO, and gaseous toxics after retrofit of the REO catalyst. In particular, the relative unit health risk associated with the decrease in emissions of airborne toxic compounds using unleaded Chinese fuel was reduced from 6.33 to 0.30. (Use of low-sulfur California Phase II gasoline rather than current in-use Chinese fuel reduced emissions further.) Following implementation of the program, a follow-up study showed that in-use emissions benefits were considerably less than anticipated, primarily because of poor quality control at the retrofit service centers, a less aggressive preretrofit maintenance procedure, and unauthorized modification to the recommended retrofit control system. Overall results indicate that a carefully controlled retrofit program using REO catalyst technology can reduce emissions significantly. However, well-defined implementation guidelines, and strict adherence to these guidelines are needed to achieve maximum benefits.     

The effects of the catalytic converter and fuel sulfur level on motor vehicle particulate matter emissions: gasoline vehicles

Scanning mobility and electrical low-pressure impactor particle size measurements conducted during chassis dynamometer testing reveal that neither the catalytic converter nor the fuel sulfur content has a significant effect on gasoline vehicle tailpipe particulate matter (PM) emissions. For current technology, port fuel injection, gasoline engines, particle number emissions are < or = 2 times higher from vehicles equipped with blank monoliths as compared to active catalysts, insignificant in contrast to the 90+% removal of hydrocarbons. PM mass emission rates derived from the size distributions are equal within the experimental uncertainty of 50-100%. Gravimetric measurements exhibit a 3-10-fold PM mass increase when the active catalyst is omitted, which is attributed to gaseous hydrocarbons adsorbing onto the filter medium. Both particle number and gravimetric measurements show that gasoline vehicle tailpipe PM emissions are independent (within 2 mg/mi) of fuel sulfur content over the 30-990 ppm concentration range. Nuclei mode sulfate aerosol is not observed in either test cell measurements or during wind tunnel testing. For three-way catalyst equipped vehicles, the principal sulfur emission is SO2; however a sulfur balance is not obtained over the drive cycle. Instead, sulfur is stored on the catalyst during moderate driving and then partially removed during high speed/load operation.     

CO2 emission benefit of diesel (versus gasoline) powered vehicles

Concerns regarding global warming have increased the pressure on automobile manufacturers to decrease emissions of CO2 from vehicles. Diesel vehicles have higher fuel economy and lower CO2 emissions than their gasoline counterparts. Increased penetration of diesel powered vehicles into the market is a possible transition strategy toward a more sustainable transportation system. To facilitate discussions regarding the relative merits of diesel vehicles it is important to have a clear understanding of their CO2 emission benefits. Based on European diesel and gasoline certification data, this report quantifies such CO2 reduction opportunities for cars and light duty trucks in today's vehicles and those in the year 2015. Overall, on a well-to-wheels per vehicle per mile basis, the CO2 reduction opportunity for today's vehicles is approximately 24-33%. We anticipate that the gap between diesel and gasoline well-to-wheel vehicle CO2 emissions will decrease to approximately 14-27% by the year 2015.     

Environmental implications on the oxygenation of gasoline with ethanol in the metropolitan area of Mexico City

Motor vehicle emission tests were performed on 12 in-use light duty vehicles, made up of the most representative emission control technologies in Mexico City: no catalyst, oxidative catalyst, and three way catalyst. Exhaust regulated (CO, NOx, and hydrocarbons) and toxic (benzene, formaldehyde, acetaldehyde, and 1,3-butadiene) emissions were evaluated for MTBE (5 vol %)- and ethanol (3, 6, and 10 vol %)-gasoline blends. The most significant overall emissions variations derived from the use of 6 vol % ethanol (relative to a 5% MTBE base gasoline) were 16% decrease in CO, 28% reduction in formaldehyde, and 80% increase in acetaldehyde emissions. A 26% reduction in CO emissions from the oldest fleet (< MY 1991, without catalytic converter), which represents about 44% of the in-use light duty vehicles in Mexico city, can be attained when using 6 vol% ethanol-gasoline, without significant variation in hydrocarbons and NOx emissions, when compared with a 5% vol MTBE-gasoline. On the basis of the emissions results, an estimation of the change in the motor vehicle emissions of the metropolitan area of Mexico city was calculated for the year 2010 if ethanol were to be used instead of MTBE, and the outcome was a considerable decrease in all regulated and toxic emissions, despite the growing motor vehicle population.     

Modeling switchgrass derived cellulosic ethanol distribution in the United States

Discussions of alternative fuel and propulsion technologies for transportation often overlook the infrastructure required to make these options practical and cost-effective. We estimate ethanol production facility locations and use a linear optimization model to consider the economic costs of distributing various ethanol fuel blends to all metropolitan areas in the United States. Fuel options include corn-based E5 (5% ethanol, 95% gasoline) to E16 from corn and switchgrass, as short-term substitutes for petroleum-based fuel. Our estimates of 1-2 cents per L of ethanol blend for downstream rail or truck transportation remain a relatively small fraction of total fuel cost. However, for even the relatively small blends of ethanol modeled, the transportation infrastructure demands would be comparably larger than the current demands of petroleum. Thus if ethanol is to be competitive in the long run, then in addition to process efficiency improvements, more efficient transportation infrastructure will need to be developed, such as pipelines. In addition to these results, national and regional policy challenges on how to pay for and optimize a new fuel and distribution infrastructure in the United States are discussed.     

Studying the effect on system preference by varying coproduct allocation in creating life-cycle inventory

How one models the input and output data for a life-cycle assessment (LCA) can greatly affect the results. Although much attention has been paid to allocation methodology by researchers in the field, specific guidance is still lacking: Earlier research focused on the effects of applying various allocation schemes to industrial processes when creating life-cycle inventories. To determine the impact of different allocation approaches upon product choice, this study evaluated the gas- and water-phase emissions during the production, distribution, and use of three hypothetical fuel systems (data that represent conventional gasoline and gasoline with 8.7 and 85% ethanol were used as the basis for modeling). This paper presents an explanation of the allocation issue and the results from testing various allocation schemes (weight, volume, market value, energy, and demand-based) when viewed across the entire system. Impact indicators for global warming, ozone depletion, and human health noncancer (water impact) were lower for the ethanol-containing fuels, while impact indicators for acidification, ecotoxicity, eutrophication, human health criteria, and photochemical smog were lower for conventional gasoline (impacts for the water-related human health cancer category showed mixed results). The relative ranking of conventional gasoline in relation to the ethanol-containing fuels was consistent in all instances, suggesting that, in this case study, the choice of allocation methodology had no impact on indicating which fuel has lower environmental impacts.     

Lubricating oil and fuel contributions to particulate matter emissions from light-duty gasoline and heavy-duty diesel vehicles

Size-resolved particulate matter emissions from heavy-duty diesel vehicles (HDDVs) and light-duty gasoline vehicles (LDGVs) operated under realistic driving cycles were analyzed for elemental carbon (EC), organic carbon (OC), hopanes, steranes, and polycyclic aromatic hydrocarbons. Measured hopane and sterane size distributions did not match the total carbon size distribution in most cases, suggesting that lubricating oil was not the dominant source of particulate carbon in the vehicle exhaust. A regression analysis using 17alpha(H)-21beta(H)-29-norhopane as a tracer for lubricating oil and benzo[ghi/perylene as a tracer for gasoline showed that gasoline fuel and lubricating oil both make significant contributions to particulate EC and OC emissions from LDGVs. A similar regression analysis performed using 17alpha(H)-21beta(H)-29-norhopane as a tracer for lubricating oil and flouranthene as a tracerfor diesel fuel was able to explain the size distribution of particulate EC and OC emissions from HDDVs. The analysis showed that EC emitted from all HDDVs operated under relatively high load conditions was dominated by diesel fuel contributions with little EC attributed to lubricating oil. Particulate OC emitted from HDDVs was more evenly apportioned between fuel and oil contributions. EC emitted from LDGVs operated underfuel-rich conditions was dominated by gasoline fuel contributions. OC emitted from visibly smoking LDGVs was mostly associated with lubricating oil, but OC emitted from all other categories of LDGVs was dominated by gasoline fuel. The current study clearly illustrates that fuel and lubricating oil make separate and distinct contributions to particulate matter emissions from motor vehicles. These particles should be tracked separately during ambient source apportionment studies since the atmospheric evolution and ultimate health effects of these particles may be different. The source profiles for fuel and lubricating oil contributions to EC and OC emissions derived in this study provide a foundation for future source apportionment calculations.     

Spatial applicability of emission factors for modeling mobile emissions

Driving cycles are used to create mobile emission factors. Emission factors are, in turn, used to estimate mobile source inventories, provide standards for new vehicle emissions testing, and facilitate comparisons of laboratory experiments. This study examines the spatial representativeness of the driving cycles underlying California's CO, THC, and NOx emission rates that are applied when estimating regional mobile emissions inventories. Sixteen randomly selected vehicles were tested on a laboratory dynamometer using driving cycles representative of driving in different cities. A total of 214 tests, with repetitions, representing six driving cycles, were conducted on the 16 vehicles. We used a random effects analysis of variance to statistically examine the differences in the resulting emission rates. The study results suggest that California mobile source pollutant inventories prepared using emission rates based on the standard drive cycle may be off by as much as 30% for regions where traffic congestion and roadway networks differ significantly from those of Los Angeles.     

Current and future linked responses of ozone and PM2.5 to emission controls

Responses of ozone and PM2.5 to emission changes are coupled because of interactions between their precursors. Here we show the interdependencies of ozone and PM2.5 responses to emission changes in 2001 and 2050, with the future case accounting for both currently planned emission controls and climate change. Current responses of ozone and PM2.5 to emissions are quantified and linked on a daily basis for five cities in the continental United States: Atlanta, Chicago, Houston, Los Angeles, and NewYork. Reductions in anthropogenic NO(x) emissions decrease 24-h average PM2.5 levels but may either increase or decrease daily maximum 8-h average ozone levels. Regional ozone maxima for all the cities are more sensitive to NO(x) reductions than at the city center, particularly in New York and Chicago. Planned controls of anthropogenic NO(x) emissions lead to more positive responses to NO(x) reductions in the future. Sensitivities of ozone and PM2.5 to anthropogenic VOC emissions are predicted to decrease between 2001 and 2050. Ammonium nitrate formation is predicted to be less ammonia-sensitive in 2050 than 2001 while the opposite is true for ammonium sulfate. Sensitivity of PM2.5 to SO2 and NO(x) emissions changes little between 2001 and 2050. Both ammonium sulfate and ammonium nitrate are predicted to decrease in sensitivity to SO2 and NO(x) emissions between 2001 and 2050. The complexities, linkages, and daily changes in the pollutant responses to emission changes suggest that strategies developed to meet specific air quality standards should consider other air quality impacts as well.     

Policy implications of uncertainty in modeled life-cycle greenhouse gas emissions of biofuels

Biofuels have received legislative support recently in California's Low-Carbon Fuel Standard and the Federal Energy Independence and Security Act. Both present new fuel types, but neither provides methodological guidelines for dealing with the inherent uncertainty in evaluating their potential life-cycle greenhouse gas emissions. Emissions reductions are based on point estimates only. This work demonstrates the use of Monte Carlo simulation to estimate life-cycle emissions distributions from ethanol and butanol from corn or switchgrass. Life-cycle emissions distributions for each feedstock and fuel pairing modeled span an order of magnitude or more. Using a streamlined life-cycle assessment, corn ethanol emissions range from 50 to 250 g CO(2)e/MJ, for example, and each feedstock-fuel pathway studied shows some probability of greater emissions than a distribution for gasoline. Potential GHG emissions reductions from displacing fossil fuels with biofuels are difficult to forecast given this high degree of uncertainty in life-cycle emissions. This uncertainty is driven by the importance and uncertainty of indirect land use change emissions. Incorporating uncertainty in the decision making process can illuminate the risks of policy failure (e.g., increased emissions), and a calculated risk of failure due to uncertainty can be used to inform more appropriate reduction targets in future biofuel policies.     

Life cycle assessment of automobile/fuel options

We examine the possibilities for a "greener" car that would use less material and fuel, be less polluting, and would have a well-managed end-of-life. Light-duty vehicles are fundamental to our economy and will continue to be for the indefinite future. Any redesign to make these vehicles greener requires consumer acceptance. Consumer desires for large, powerful vehicles have been the major stumbling block in achieving a "green car". The other major barrier is inherent contradictions among social goals such as fuel economy, safety, low emissions of pollutants, and low emissions of greenhouse gases, which has led to conflicting regulations such as emissions regulations blocking sales of direct injection diesels in California, which would save fuel. In evaluating fuel/vehicle options with the potential to improve the greenness of cars [diesel (direct injection) and ethanol in internal combustion engines, battery-powered, gasoline hybrid electric, and hydrogen fuel cells], we find no option dominates the others on all dimensions. The principles of green design developed by Anastas and Zimmerman (Environ. Sci. Technol. 2003, 37, 94A-101A) and the use of a life cycle approach provide insights on the key sustainability issues associated with the various options.     

Electric vehicles in China: emissions and health impacts

E-bikes in China are the single largest adoption of alternative fuel vehicles in history, with more than 100 million e-bikes purchased in the past decade and vehicle ownership about 2× larger for e-bikes as for conventional cars; e-car sales, too, are rapidly growing. We compare emissions (CO(2), PM(2.5), NO(X), HC) and environmental health impacts (primary PM(2.5)) from the use of conventional vehicles (CVs) and electric vehicles (EVs) in 34 major cities in China. CO(2) emissions (g km(-1)) vary and are an order of magnitude greater for e-cars (135-274) and CVs (150-180) than for e-bikes (14-27). PM(2.5) emission factors generally are lower for CVs (gasoline or diesel) than comparable EVs. However, intake fraction is often greater for CVs than for EVs because combustion emissions are generally closer to population centers for CVs (tailpipe emissions) than for EVs (power plant emissions). For most cities, the net result is that primary PM(2.5) environmental health impacts per passenger-km are greater for e-cars than for gasoline cars (3.6× on average), lower than for diesel cars (2.5× on average), and equal to diesel buses. In contrast, e-bikes yield lower environmental health impacts per passenger-km than the three CVs investigated: gasoline cars (2×), diesel cars (10×), and diesel buses (5×). Our findings highlight the importance of considering exposures, and especially the proximity of emissions to people, when evaluating environmental health impacts for EVs.     

美国国内使用酒精汽油的情况(二)

美国乙醇进口占总供应量的7 % ,允许免税。国家决定乙醇混合油免税以此保证国内酒精工业持续发展。减税酒精汽油中不得超过10%的酒精。含85 %酒精、15%汽油的E85混合燃料也正在美国试用 ,一种加入添加剂结合乙醇的产品与柴油燃料混合对冷起动性能有所改进。乙醇与异丁烯结合生产增氧剂的环保替代品 ,是最经济的增氧剂。(孙悟)