Abstract  There is a strong need to manage low-value forest residues generated from the management practices associated with wildfire, pest, and disease control strategies to improve both the environmental and economic sustainability of forestlands. The conversion of this woody biomass into value-added products provides a great opportunity to benefit both the environment and economy. This study aimed to assess the environmental impacts of converting forest residues into two renewable fuels, cellulosic ethanol and biomethane, by different biochemical conversion pathways. The energy balances and environmental impacts, including acidification, eutrophication, global warming, and photochemical ozone formation, of the two biorefinery approaches were addressed. This work illustrated the advantages of converting forest residues into biomethane from energy and environmental perspectives. The tradeoff between the economic benefits and potential environmental issues need to be carefully considered.

Abstract  Expanding the domestic bioeconomy can help diversify the use of national resources and reduce emissions. Evaluating the sustainability of a growing bioeconomy, however, is inherently complex since it spans several sectors and supply chains. It requires a comprehensive, integrated analysis framework to assess the developments across the traditional sustainability dimensions. Further, the assessment of bioeconomy developments requires a robust baseline of historic data and trends. In this paper, we analyze the evolution of the biofuel portion of the US bioeconomy, focusing on two fuels that had an exponential growth in the last two decades: corn ethanol and soybean biodiesel. For this purpose, we created a novel time series of harmonized environmentally-extended input-output (EEIO) tables based on a publicly available model from the US Environmental Protection Agency and expanded its disaggregation to reflect the main supply chains of the biofuels sectors. The EEIO time series provides the historical evolution of these biofuels relative to the rest of the economy as well as on an energy-unit basis. We find that, except for energy use, the broader US economy declined in both resource intensity and most environmental impacts when normalized per one million dollars of gross domestic product. Deviating from this trend are freshwater ecotoxicity and human toxicity, mainly attributable to the expansion of commodity crops and the increase of domestic oil and gas extraction respectively. We also find that the biofuel industry's total socioeconomic, resource use and environmental impacts grew with their production increases over time. However, the industry's maturation and scale-up, combined with higher feedstock yields, contributed to a reduction of most impacts on an energy-unit basis over time.

Abstract  Using Greenhouse Gas Reporting Program data (GHGRP) and National Emissions Inventory data from 2014, we investigate U.S. refinery greenhouse gas (GHG) emissions (CO2, CH4, and N2O) and criteria air pollutant (CAP) emissions (VOC, CO, NOx, SO2, PM10, and PM2.5). The study derives (1) combustion emission factors (EFs) of refinery fuels (e.g., refinery catalyst coke and refinery combined gas), (2) U.S. refinery GHG emissions and CAP emissions per crude throughput at the national and regional levels, and (3) GHG and CAP emissions attributable to U.S. refinery products. The latter two emissions were further itemized by source: combustion emission, process emission, and facility-wide emission. We estimated U.S. refinery product GHG and CAP emissions via energy allocation at the refinery process unit level. The unit energy demand and unit flow information were adopted from the Petroleum Refinery Life Cycle Inventory Model (PRELIM version 1.1) by fitting individual U.S. refineries. This study fills an important information gap because it (1) evaluates refinery CAP emissions along with GHG emissions and (2) provides CAP and GHG emissions not only for refinery main products (gasoline, diesel, jet fuel, etc.) but also for refinery secondary products (asphalt, lubricant, wax, light olefins, etc.).

Abstract  Alkali and alkaline earth metal impurities found in diesel fuels are potential poisons for diesel exhaust catalysts. Using an accelerated aging procedure, a set of production exhaust systems from a 2011 Ford F250 equipped with a 6.7L diesel engine have been aged to an equivalent of 150,000 miles of thermal aging and metal exposure. These exhaust systems included a diesel oxidation catalyst (DOC), selective catalytic reduction (SCR) catalyst, and diesel particulate filter (DPF). Four separate exhaust systems were aged, each with a different fuel: ULSD containing no measureable metals, B20 containing sodium, B20 containing potassium and B20 containing calcium. Metals levels were selected to simulate the maximum allowable levels in B100 according to the ASTM D6751 standard. Analysis of the aged catalysts included Federal Test Procedure emissions testing with the systems installed on a Ford F250 pickup, bench flow reactor testing of catalyst cores, and electron probe microanalysis (EPMA). The thermo-mechanical properties of the aged DPFs were also measured. EPMA imaging of aged catalyst parts found that both the Na and K penetrated into the washcoat of the DOC and SCR catalysts, while Ca remained on the surface of the washcoat. Bench flow reactor experiments were used to measure the standard NOx conversion, NH3 storage and NH3 oxidation for each of the aged SCR catalysts. Flow reactor results showed that the first inch of the SCR catalysts exposed to Na and K had reduced NOx conversion through a range of temperatures and also had reduced NH3 storage capacity. The SCR catalyst exposed to Ca had similar NOx conversion and NH3 storage performance compared to the catalyst aged with ULSD. Using a chassis dynamometer, vehicle emissions tests were conducted with each of the aged catalyst systems installed onto a Ford F250 pickup. Regardless of the evidence of catalyst deactivation seen in flow reactor experiments and EPMA imaging, the vehicle successfully passed the 0.2 gram/mile NOx emission standard with each of the four aged exhaust systems. This indicates that total catalyst volume is adequate to accommodate the catalyst activity loss observed in the flow reactor experiments.

Abstract  A pilot study was performed to explore the effects of PM Index, low and high molecular weight aromatics, and ethanol content on particulate matter (PM) emissions from light-duty Tier 2 gasoline vehicles. Four test vehicles from model years 2007-2009 were tested on seven fuels spanning PM Index values from 0.9 to 2.7, aromatic content from 14 to 38%, and ethanol content from 0 to 15%. Three of the test vehicles were port fuel injected (PFI) while the fourth featured gasoline direct injection (GDI). In an earlier program, two of the PFI vehicles demonstrated high sensitivity of PM emissions to fuel property changes while the third showed low sensitivity. The sensitivity of the GDI vehicle to fuel property changes was not known prior to this study. The vehicles were tested over the LA92 and US06 test cycles at 24°C (75°F). PM and regulated gaseous emissions were measured by test phase. Second-by-second tailpipe soot emissions were measured using the AVL Micro Soot Sensor. The results of this study support the theory behind the PM Index that low volatility compounds, particularly heavy aromatics, have the strongest influence on PM emissions from gasoline vehicles. In addition, the presence of ethanol was found to have a reinforcing interaction with PM Index in PFI vehicles, consistent with results reported in a companion paper [1]. The GDI vehicle generally produced higher PM emissions than the PFI vehicles, most notably during operation on the lower-PM-Index fuels.

Abstract  Forest residue is a major potential feedstock for second generation biofuel, however little knowledge exists about environmental impacts of development and production of biofuel from such a feedstock. Using a high-resolution regional air quality model, we estimate the air quality impacts of an aviation biofuel supply chain scenario in the Pacific Northwest of the United States that uses forest residue as the feedstock. Pollutant emissions for the major supply chain components including feedstock harvesting, transportation, and biorefinery operations were compiled. Using two potential supply chain regions, we find that biomass and biofuel hauling activities will add <1% of vehicle miles travelled to existing traffic, but the biorefineries will add significant local sources of NOxand CO. Simulations of various biomass utilization scenarios show that while the regional average increase of PM2.5and O3from the supply chain is small, the 8-hour maximum summer time O3can increase by 1-2 ppb and 24-hr average maximum PM2.5by 2 µg/m3. We also show that these increased PM2.5concentrations from the supply chain are much smaller compared to slash pile burning, which can increase average PM2.5by 2-5 µg/m3. Using BenMAP, a health impact assessment tool, we show that there are health benefits associated with avoided slash pile burning, and results indicate a decrease in premature deaths as well as several other non-fatal and minor health effects. In general, the aviation biofuel supply chain using forest residue as a feedstock is expected to have an overall air quality benefit that results primarily from the avoided slash pile burning emissions.

Abstract  The application of nitrification inhibitors (NIs) is effective in suppressing nitrification and N2O emissions while promoting crop yields in many agroecosystems. However, the inhibitory effects of different NIs for vegetable production under soil and environmental conditions in China are not fully understood. To evaluate the effects of chemical and biological NIs on N2O emissions and the nitrogen use efficiency (NUE), a 2-yr field experiment with four treatments (regular urea (Urea), urea + dicyandiamide (DCD), urea + nitrapyrin (CP) and urea + biological nitrification inhibitor (BNI)) performed in triplicate was carried out in an intensive vegetable field using the static chamber and gas chromatography method. The results showed that the CP and BNI treatments shifted the main form of soil inorganic nitrogen (N) from nitrate (NO3-), which was the case for the Urea and DCD treatments, to ammonium (NH4+). The variations in soil temperature, moisture and NO3- content regulated the seasonal fluctuations of N2O emissions. Moreover, the DCD treatment did not significantly affect N2O or agronomic NUE relative to the Urea treatment, while CP and BNI significantly decreased annual N2O emissions by 16.5% and 18.1% and improved NUE by 12.6% and 6.7%, respectively. Thus, a markedly lower global warming potential (GWP) and greenhouse gas intensity (GHGI) was observed in the CP and BNI treatments relative to the Urea and DCD treatments. The results demonstrated that the NIs played important roles in enhancing yields and reducing N2O emissions from the vegetable ecosystem and that the CP and BNI treatments are suitable for marketing in China. (C) 2014 Elsevier B.V. All rights reserved.

Abstract  This paper describes the development of (1) a formula correlating the variation in overall refinery energy efficiency with crude quality, refinery complexity, and product slate; and (2) a methodology for calculating energy and greenhouse gas (GHG) emission intensities and processing fuel shares of major U.S. refinery products. Overall refinery energy efficiency is the ratio of the energy present in all product streams divided by the energy in all input streams. Using linear programming (LP) modeling of the various refinery processing units, we analyzed 43 refineries that process 70% of total crude input to U.S. refineries and cover the largest four Petroleum Administration for Defense District (PADD) regions (I, II, III, V). Based on the allocation of process energy among products at the process unit level, the weighted-average product-specific energy efficiencies (and ranges) are estimated to be 88.6% (86.2%-91.2%) for gasoline, 90.9% (84.8%-94.5%) for diesel, 95.3% (93.0%-97.5%) for jet fuel, 94.5% (91.6%-96.2%) for residual fuel oil (RFO), and 90.8% (88.0%-94.3%) for liquefied petroleum gas (LPG). The corresponding weighted-average, production GHG emission intensities (and ranges) (in grams of carbon dioxide-equivalent (CO2e) per megajoule (MJ)) are estimated to be 7.8 (6.2-9.8) for gasoline, 4.9 (2.7-9.9) for diesel, 2.3 (0.9-4.4) for jet fuel, 3.4 (1.5-6.9) for RFO, and 6.6 (4.3-9.2) for LPG. The findings of this study are key components of the life-cycle assessment of GHG emissions associated with various petroleum fuels; such assessment is the centerpiece of legislation developed and promulgated by government agencies in the United States and abroad to reduce GHG emissions and abate global warming.