Comparison of Life Cycle Greenhouse Gases from Natural Gas Pathways for Light-Duty Vehicles

Low prices and abundant resources open new opportunities for using natural gas, one of which is the production of transportation fuels. In this study, we use a Monte Carlo analysis combined with a life cycle analysis framework to assess the greenhouse gas (GHG) implications of a transition to natural gas-powered vehicles. We consider six different natural gas fuel pathways in two representative light-duty vehicles: a passenger vehicle and a sport utility vehicle. We find that a battery electric vehicle (BEV) powered with natural gas-based electricity achieves around 40% life cycle emissions reductions when compared to conventional gasoline. Gaseous hydrogen fuel cell electric vehicles (FCEVs) and compressed natural gas (CNG) vehicles have comparable life cycle emissions with conventional gasoline, offering limited reductions with 100-year global warming potential (GWP) yet leading to increases with 20-year GWP. Other liquid fuel pathways (methanol, ethanol, and Fischer–Tropsch liquids) have larger GHG emissions than conventional gasoline even when carbon capture and storage technologies are available. Life cycle GHG emissions of natural gas pathways are sensitive to the vehicle fuel efficiency, to the methane leakage rates of natural gas systems, and to the GWP assumed. With the current vehicle technologies, the break-even methane leakage rates of CNG, gaseous hydrogen FCEV, and BEV are 0.9%/2.3%, 1.2%/2.8%, and 4.5%/10.8% (20-year GWP/100-year GWP). If the actual methane leakage rate is lower than the break-even rate of a specific natural gas pathway, that natural gas pathway reduces GHG emissions compared to conventional gasoline; otherwise, it leads to an increase in emissions

Comparison of Life Cycle Greenhouse Gases from Natural Gas Pathways for Medium and Heavy-Duty Vehicles

The low-cost and abundant supply of shale gas in the United States has increased the interest in using natural gas for transportation. We compare the life cycle greenhouse gas (GHG) emissions from different natural gas pathways for medium and heavy-duty vehicles (MHDVs). For Class 8 tractor-trailers and refuse trucks, none of the natural gas pathways provide emissions reductions per unit of freight-distance moved compared to diesel trucks. When compared to the petroleum-based fuels currently used in these vehicles, CNG and centrally produced LNG increase emissions by 0–3% and 2–13%, respectively, for Class 8 trucks. Battery electric vehicles (BEVs) powered with natural gas-produced electricity are the only fuel-technology combination that achieves emission reductions for Class 8 transit buses (31% reduction compared to the petroleum-fueled vehicles). For non-Class 8 trucks (pick-up trucks, parcel delivery trucks, and box trucks), BEVs reduce emissions significantly (31–40%) compared to their diesel or gasoline counterparts. CNG and propane achieve relatively smaller emissions reductions (0–6% and 19%, respectively, compared to the petroleum-based fuels), while other natural gas pathways increase emissions for non-Class 8 MHDVs. While using natural gas to fuel electric vehicles could achieve large emission reductions for medium-duty trucks, the results suggest there are no great opportunities to achieve large emission reductions for Class 8 trucks through natural gas pathways with current technologies. There are strategies to reduce the carbon footprint of using natural gas for MHDVs, ranging from increasing vehicle fuel efficiency, reducing life cycle methane leakage rate, to achieving the same payloads and cargo volumes as conventional diesel trucks

Comparison of Life Cycle Greenhouse Gases from Natural Gas Pathways for Light-Duty Vehicles

Low prices and abundant resources open new opportunities for using natural gas, one of which is the production of transportation fuels. In this study, we use a Monte Carlo analysis combined with a life cycle analysis framework to assess the greenhouse gas (GHG) implications of a transition to natural gas-powered vehicles. We consider six different natural gas fuel pathways in two representative light-duty vehicles: a passenger vehicle and a sport utility vehicle. We find that a battery electric vehicle (BEV) powered with natural gas-based electricity achieves around 40% life cycle emissions reductions when compared to conventional gasoline. Gaseous hydrogen fuel cell electric vehicles (FCEVs) and compressed natural gas (CNG) vehicles have comparable life cycle emissions with conventional gasoline, offering limited reductions with 100-year global warming potential (GWP) yet leading to increases with 20-year GWP. Other liquid fuel pathways (methanol, ethanol, and Fischer–Tropsch liquids) have larger GHG emissions than conventional gasoline even when carbon capture and storage technologies are available. Life cycle GHG emissions of natural gas pathways are sensitive to the vehicle fuel efficiency, to the methane leakage rates of natural gas systems, and to the GWP assumed. With the current vehicle technologies, the break-even methane leakage rates of CNG, gaseous hydrogen FCEV, and BEV are 0.9%/2.3%, 1.2%/2.8%, and 4.5%/10.8% (20-year GWP/100-year GWP). If the actual methane leakage rate is lower than the break-even rate of a specific natural gas pathway, that natural gas pathway reduces GHG emissions compared to conventional gasoline; otherwise, it leads to an increase in emissions

Can Switching from Coal to Shale Gas Bring Net Carbon Reductions to China?

To increase energy security and reduce emissions of air pollutants and CO₂ from coal use, China is attempting to duplicate the rapid development of shale gas that has taken place in the United States. This work builds a framework to estimate the lifecycle greenhouse gas (GHG) emissions from China’s shale gas system and compares them with GHG emissions from coal used in the power, residential, and industrial sectors. We find the mean lifecycle carbon footprint of shale gas is about 30–50% lower than that of coal in all sectors under both 20 year and 100 year global warming potentials (GWP₂₀ and GWP₁₀₀). However, primarily due to large uncertainties in methane leakage, the upper bound estimate of the lifecycle carbon footprint of shale gas in China could be approximately 15–60% higher than that of coal across sectors under GWP₂₀. To ensure net GHG emission reductions when switching from coal to shale gas, we estimate the breakeven methane leakage rates to be approximately 6.0%, 7.7%, and 4.2% in the power, residential, and industrial sectors, respectively, under GWP₂₀. We find shale gas in China has a good chance of delivering air quality and climate cobenefits, particularly when used in the residential sector, with proper methane leakage control

Block of neonatal rat cortical sodium and potassium channels by DEET and related compounds.

<p>A) Inward sodium currents activated by a 15 msec pulse to 0 mV from a holding potential of −80 mV. Control is the peak inward sodium current before treatment. Increasing DEET concentrations blocked the current, each trace taken after 1 min incubation in drug, and there was little change thereafter. Each trace is matched in form to treatment: thick line, Control; thin line, Washout; dashed line, 100 µM DEET; dotted line, 300 µM DEET; and dotted/dashed line, 1 mM DEET. B) Concentration-response curves generated from peak sodium currents as shown in A, replicated across different cells treated with DEET (n = 3), toluene (n = 6), or lidocaine (n = 4). Symbols are mean percentage of control current amplitude, with each concentration of blocker replicated 3–6 times. Error bars represent SEM of currents. C) Typical outward currents activated by a 500 msec pulse to +60 mV from a holding potential of −80 mV, and displayed concentration-dependent block by DEET. D) Typical current-voltage relationships and DEET inhibition of potassium currents in rat cortical neurons. Currents were evoked by stepping the membrane voltage between −100 and +100 mV in 20 mV increments from a holding potential of −80 mV. Amplitude of the sustained current was calculated at 200 msec. E) Concentration-response curves for DEET-mediated inhibition of rat neuronal potassium channels from recordings as shown in C, using responses at +60 mV. Symbols are mean percentage of control current amplitude, and error bars represent SEM of currents replicated across different cells (n≥3).</p

Effect of phentolamine on the activity of DEET (A), octopamine (B), propoxur (C) and 4-AP (D) on discharge rates of housefly larvae CNS preparations (n = 3–5 preparations per curve, with each concentration replicated 3–5 times).

<p>Data points represent mean percentage increase of baseline firing rate, and error bars represent SEM of drug concentrations replicated at least 3 times. When error bars are absent, it is because they are smaller than the size of the symbol. Data points at each concentration for drug alone were compared to drug + phentolamine, and statistical significance (t-test, P<0.05) is indicated by an asterisk.</p

Neurophysiological recordings from the CNS of third instar larvae of <i>M.</i> domestica A) Nerve discharges before and after DEET, toluene, and lidocaine treatment across different CNS preparations, as indicated.

<p>Initial firing frequencies in spikes/second (Hz) for each experiment are given to the left of each trace. B) Concentration-response curves for DEET, toluene, and lidocaine on CNS nerve discharge of <i>M. domestica</i> larvae from replicated recordings (n = 4–5 preparations per curve, with each concentration replicated 4 times), as shown in A. Data points represent mean percentage increase of baseline firing rate, and error bars represent SEM of drug concentrations replicated at least 3 times. When error bars are absent, it is because they are smaller than the size of the symbol.</p

AChE inhibition data expressed as mean (n = 3) IC₅₀ values.

<p>Inhibition values of <i>Md</i>AChE, <i>Dm</i>AChE, and hAChE were analyzed by one-way ANOVA followed by Tukey's multiple comparison test. Letters after 95% confidence intervals (CI) represent statistical significance for IC₅₀ values among enzymes tested with DEET. IC₅₀s for DEET not labeled by the same letter represent statistical significance (P<0.05).</p

Effects of DEET on octopaminergic systems in firefly and <i>Sf</i>21 cells.

<p>A) Dose-dependent action of DEET, CDM, and propoxur on the light organ of the firefly, <i>Photinus pyralis</i>. See text for explanation. B) Activation of an octopamine receptor in <i>Sf</i>21 cells shown by internal calcium fluorescence. Bars represent means of normalized fluorescence with error bars denoting SEM, replicated across individual plates of cells (n = 3). Statistics for each column were determined by a paired t-test against matched control raw fluorescent values, where an asterisk represents statistical significance at P<0.05. For labels, OA =  octopamine and PA =  phentolamine. All compounds were applied at 100 µM.</p

Chemical structures of the pharmacological agents used in this study.

<p>Chemical structures of the pharmacological agents used in this study.</p