Achieving Deep Cuts in the Carbon Intensity of U.S. Automobile Transportation by 2050: Complementary Roles for Electricity and Biofuels

Passenger cars in the United States (U.S.) rely primarily on petroleum-derived fuels and contribute the majority of U.S. transportation-related greenhouse gas (GHG) emissions. Electricity and biofuels are two promising alternatives for reducing both the carbon intensity of automotive transportation and U.S. reliance on imported oil. However, as standalone solutions, the biofuels option is limited by land availability and the electricity option is limited by market adoption rates and technical challenges. This paper explores potential GHG emissions reductions attainable in the United States through 2050 with a county-level scenario analysis that combines ambitious plug-in hybrid electric vehicle (PHEV) adoption rates with scale-up of cellulosic ethanol production. With PHEVs achieving a 58% share of the passenger car fleet by 2050, phasing out most corn ethanol and limiting cellulosic ethanol feedstocks to sustainably produced crop residues and dedicated crops, we project that the United States could supply the liquid fuels needed for the automobile fleet with an average blend of 80% ethanol (by volume) and 20% gasoline. If electricity for PHEV charging could be supplied by a combination of renewables and natural-gas combined-cycle power plants, the carbon intensity of automotive transport would be 79 g CO2e per vehicle-kilometer traveled, a 71% reduction relative to 2013

Archaeology and art in context: Excavations at the Gunu site complex, northwest Kimberley, Western Australia

Copyright: 2020 Moore et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. The Kimberley region of Western Australia is one of the largest and most diverse rock art provenances in the world, with a complex stylistic sequence spanning at least 16 ka, culminating in the modern art-making of the Wunumbal people. The Gunu Site Complex, in the remote Mitchell River region of the northwest Kimberley, is one of many local expressions of the Kimberley rock art sequence. Here we report excavations at two sites in this complex: Gunu Rock, a sand sheet adjacent to rock art panels; and Gunu Cave, a floor deposit within an extensive rockshelter. Excavations at Gunu Rock provide evidence for two phases of occupation, the first from 7-8 to 2.7 ka, and the second from 1064 cal BP. Excavations at Gunu Rock provide evidence for occupation from the end of the second phase to the recent past. Stone for tools in the early phase were procured from a variety of sources, but quartz crystal reduction dominated the second occupation phase. Small quartz crystals were reduced by freehand percussion to provide small flake tools and blanks for manufacturing small points called nguni by the Wunambal people today. Quartz crystals were prominent in historic ritual practices associated with the Wanjina belief system. Complex methods of making bifacially-thinned and pressure flaked quartzite projectile points emerged after 2.7 ka. Ochre pigments were common in both occupation phases, but evidence for occupation contemporaneous with the putative age of the oldest rock art styles was not discovered in the excavations. Our results show that developing a complete understanding of rock art production and local occupation patterns requires paired excavations inside and outside of the rockshelters that dominate the Kimberley

Switchable ionic liquids based on di-carboxylic acids for one-pot conversion of biomass to an advanced biofuel

Certain ionic liquids have recently been developed as effective solvents for biomass pretreatment, but their adoption has been limited due to availability, production costs, and inhibitory effects on conventional enzymes and microorganisms. We describe here a novel class of ionic liquids based on di-carboxylic acids that have high pretreatment efficiency and are compatible with both commercial enzyme mixtures and microbial fermentation host organisms. This system takes advantage of the two ionization states of di-carboxylic acids to switch from a basic solution that pretreats biomass effectively to an acidic solution with conditions favorable for cellulases and back again for the next round of pretreatment. Lab-scale reactions show 90% conversion of lignocellulosic biomass to fermentable sugars using commercial enzyme mixtures in a one-pot process. We then demonstrate E. coli fermentation of the resulting crude hydrolysate to produce isopentenol without removal of the ionic liquid or inhibitors prior to fermentation. This new process yields high biomass conversion and eliminates several technical and economic problems associated with current ionic liquid-based processes. Our preliminary techno-economic analysis (TEA) suggests biorefineries designed to use these switchable ILs can reduce the minimum selling price (MSP) of their biofuel by more than $1 gal relative to biorefineries utilizing traditional ILs (e.g., [CCIm][OAc]) that have been shown to be very effective at pretreatment but inhibit downstream saccharification and fermentation processes, requiring extensive washing of the pretreated biomass