Toxic Emissions from Mobile Sources: A Total Fuel-Cycle Analysis for Conventional and Alternative Fuel Vehicles

ABSTRACT

Mobile sources are among the largest contributors of four hazardous air pollutants—benzene, 1,3-butadiene, acetal-dehyde, and formaldehyde—in urban areas. At the same time, federal and state governments are promoting the use of alternative fuel vehicles as a means to curb local air pollution. As yet, the impact of this movement toward alternative fuels with respect to toxic emissions has not been well studied. The purpose of this paper is to compare toxic emissions from vehicles operating on a variety of fuels, including reformulated gasoline (RFG), natural gas, ethanol, methanol, liquid petroleum gas (LPG), and electricity. This study uses a version of Argonne National Laboratory's Greenhouse Gas, Regulated Emissions, and Energy Use in Transportation (GREET) model, appropriately modified to estimate toxic emissions. The GREET model conducts a total fuel-cycle analysis that calculates emissions from both downstream (e.g., operation of the vehicle) and upstream (e.g., fuel production and distribution) stages of the fuel cycle. We find that almost all of the fuels studied reduce 1,3-buta-diene emissions compared with conventional gasoline (CG). However, the use of ethanol in E85 (fuel made with 85% ethanol) or RFG leads to increased acetaldehyde emissions, and the use of methanol, ethanol, and compressed natural gas (CNG) may result in increased formaldehyde emissions. When the modeling results for the four air toxics are considered together with their cancer risk factors, all the fuels and vehicle technologies show air toxic emission reduction benefits.     

A Comparative Analysis of Emissions Deterioration for In-Use Alternative Fuel Vehicles

Abstract

Although there have been several studies examining emissions from in–use alternative fuel vehicles (AFVs), little is known about the deterioration of these emissions over vehicle lifetimes and how this deterioration compares with deterioration from conventional vehicles (CVs). This paper analyzes emissions data from 70 AFVs and 70 CVs operating in the federal government fleet to determine whether AFV emissions deterioration differs significantly from CV emissions deterioration. An analysis is conducted on three alternative fuel types (natural gas, methanol, and ethanol) and on four pollutants (carbon monoxide, total hydrocarbons, non-methane hydrocarbons, and nitrogen oxides). The results indicate that for most cases studied, deterioration differences are not statistically significant; however, several exceptions (most notably with natural gas vehicles) suggest that air quality planners and regulators must further analyze AFV emissions deterioration to properly include these technologies in broader air quality management schemes.     

A New Alternative Fuel for Reduction of Polycyclic Aromatic Hydrocarbon and Particulate Matter Emissions from Diesel Engines

Abstract

This study investigated the emissions of polycyclic aromatic hydrocarbons (PAHs), carcinogenic potential of PAH and particulate matter (PM), brake-specific fuel consumption (BSFC), and power from diesel engines under transient cycle testing of six test fuels: premium diesel fuel (PDF), B100 (100% palm biodiesel), B20 (20% palm biodiesel + 80% PDF), BP9505 (95% paraffinic fuel + 5% palm biodiesel), BP8020 (80% paraffinic fuel + 20% palm biodiesel), and BP100 (100% paraffinic fuel; Table 1). Experimental results indicated that B100, BP9505, BP8020, and BP100 were much safer when stored than PDF. However, we must use additives so that B100 and BP100 will not gel as quickly in a cold zone. Using B100, BP9505, and BP8020 instead of PDF reduced PM, THC, and CO emissions dramatically but increased CO₂ slightly because of more complete combustion. The CO₂-increased fraction of BP9505 was the lowest among test blends. Furthermore, using B100, B20, BP9505, and BP8020 as alternative fuels reduced total PAHs and total benzo[a]pyrene equivalent concentration (total BaP_eq) emissions significantly. BP9505 had the lowest decreased fractions of power and torque and increased fraction of BSFC. These experimental results implied that BP9505 is feasible for traveling diesel vehicles. Moreover, paraffinic fuel will likely be a new alternative fuel in the future. Using BP9505 instead of PDF decreased PM (22.8%), THC (13.4%), CO (25.3%), total PAHs (88.9%), and total BaP_eq (88.1%) emissions significantly.     

A Probabilistic Production Costing Analysis of SO2 Emissions Reduction Strategies for Ohio: Emissions,Cost, and Employment Tradeoffs

A new approach for state- and utility-level analysis of the cost and regional economic impacts of strategies for reducing utility SO₂ emissions is summarized and applied to Ohio. The methodology is based upon probabilistic production costing and economic input-output analysis. It is an improvement over previous approaches because it: (1) accurately models random outages of generating units, “must-run” constraints on unit output, and the distribution of power demands; and (2) runs quickly on a microcomputer and yet considers the entire range of potential control strategies from a systems perspective. The input-output analysis considers not only the economic effects of utility fuel use and capital investment, but also those of increased electric rates. Two distinct strategies are found to be most attractive for Ohio. The first, more flexible one, consists of emissions dispatching (ED) alone to meet short run emissions reduction targets. A 75 percent reduction can then be achieved by the turn of the century by combining ED and fuel switching (FS) with flue gas desulfiirization, limestone Injection multistage burners, and physical coal cleaning at selected plants. The second is a scrubber-based strategy which includes ED. By the year 2000, energy conservation becomes a cost effective component of these strategies. In order to minimize compliance costs, acid rain legislation which facilitates emissions trading and places regional tonnage limits on emissions is desirable.     

Some Technical and Economic Aspects of Residual Fuel Oil Desulfurization

Combustion of residual, the most common type of fuel oil used in industrial and commercial steam generating plants, accounts for about 600,000 tons or 37 percent of the sulfur oxide emissions in New York state. On the average, residual oil available in New York state contains about 2.2 percent sulfur and is consumed at an annual rate of approximately 85 million barrels. The removal of sulfur from many types of residuals should become economically feasible as a result of the development of the HDS and H-Oil hydrodesulfurization processes. From studies recently made, these methods of desulfurization have been estimated to vary from a minimum of no appreciable increase in overall cost to a maximum of about one cent per gallon. The by-product distillates produced in hydrodesulfurization are a very significant factor in making the process economical and the demand for these is increasing at a greater rate than residual.     

Tagging Diesel and Residential Oil Furnace Emissions in Roanoke,Virginia, with Enriched Isotopes of Samarium

Stable isotopic tracers were used in Roanoke, Virginia, to tag particulate emissions from diesel trucks and residential oil furnaces, two sources of soot and PAHs which cannot be differentiated on the basis of known constituents. Approximately 1.6 g of enriched ¹⁴⁹Sm were used to tag 264 m³ of diesel fuel burned by the city bus and truck fleets; 0.39 g of ¹⁵⁰Sm were used to tag 106 m³ of residential heating oil. Picogram amounts of the tracers were determined simultaneously by thermal-ionization mass spectrometry in fine particles collected within the city at signal-to-noise ratios as large as 6000. These results demonstrate the feasibility of tracing particles from multiple combustion sources with stable, separated isotopes.     

Modeling to Evaluate Contribution of Oil and Gas Emissions to Air Pollution

Oil and gas production in the Western United States has increased considerably over the past 10 years. While many of the still limited oil and gas impact assessments have focused on potential human health impacts, the typically remote locations of production in the Intermountain West suggests that the impacts of oil and gas production on national parks and wilderness areas (Class I and II areas) could also be important. To evaluate this, we utilize the Comprehensive Air quality Model with Extensions (CAMx) with a year-long modeling episode representing the best available representation of 2011 meteorology and emissions for the Western United States. The model inputs for the 2011 episodes were generated as part of the Three State Air Quality Study (3SAQS). The study includes a detailed assessment of oil and gas (O&G) emissions in Western States. The year-long modeling episode was run both with and without emissions from O&G production. The difference between these two runs provides an estimate of the contribution of the O&G production to air quality. These data were used to assess the contribution of O&G to the 8 hour average ozone concentrations, daily and annual fine particulate concentrations, annual nitrogen deposition totals and visibility in the modeling domain. We present the results for the Class I and II areas in the Western United States. Modeling results suggest that emissions from O&G activity are having a negative impact on air quality and ecosystem health in our National Parks and Class I areas.

Implications: In this research, we use a modeling framework developed for oil and gas evaluation in the western United States to determine the modeled impacts of emissions associated with oil and gas production on air pollution metrics. We show that oil and gas production may have a significant negative impact on air quality and ecosystem health in some national parks and other Class I areas in the western United States. Our findings are of particular interest to federal land managers as well as regulators in states heavy in oil and gas production as they consider control strategies to reduce the impact of development.     

Characterization of Real-World Activity,Fuel Use,and Emissions for Selected Motor Graders Fueled with Petroleum Diesel and B20 Biodiesel

Abstract

Motor graders are a common type of nonroad vehicle used in many road construction and maintenance applications. In-use activity, fuel use, and emissions were measured for six selected motor graders using a portable emission measurement system. Each motor grader was tested with petroleum diesel and B20 biodiesel. Duty cycles were quantified in terms of the empirical cumulative distribution function of manifold absolute pressure (MAP), which is an indicator of engine load. The motor graders were operated under normal duty cycles for road maintenance and repair at various locations in Wake and Nash Counties in North Carolina. Approximately 3 hr of quality-assured, second-by-second data were obtained during each test. An empirical modal-based model of vehicle fuel use and emissions was developed, based on stratifying the data with respect to ranges of normalized MAP, to enable comparisons between duty cycles, motor graders, and fuels. Time-based emission factors were found to increase monotonically with MAP. Fuel-based emission factors were mainly sensitive to differences between idle and non-idle engine operation. Cycle average emission factors were estimated for road “resurfacing”, “roading,” and “shouldering” activities. On average, the use of B20 instead of petroleum diesel leads to a negligible decrease of 1.6% in nitric oxide emission rate, and decreases of 19– 22% in emission rates of carbon monoxide, hydrocarbons, and particulate matter. Emission rates decrease significantly when comparing newer engine tier vehicles to older ones. Significant reductions in tailpipe emissions accrue especially from the use of B20 and adoption of newer vehicles.     

Comparison of Particle Size Distributions and Elemental Partitioning from the Combustion of Pulverized Coal and Residual Fuel Oil

ABSTRACT

U.S. Environmental Protection Agency (EPA) research examining the characteristics of primary PM generated by the combustion of fossil fuels is being conducted in efforts to help determine mechanisms controlling associated adverse health effects. Transition metals are of particular interest, due to the results of studies that have shown cardiopulmonary damage associated with exposure to these elements and their presence in coal and residual fuel oils. Further, elemental speciation may influence this toxicity, as some species are significantly more water-soluble, and potentially more bio-available, than others. This paper presents results of experimental efforts in which three coals and a residual fuel oil were combusted in three different systems simulating process and utility boilers. Particle size distributions (PSDs) were determined using atmospheric and low-pressure impac-tion as well as electrical mobility, time-of-flight, and light-scattering techniques. Size-classified PM samples from this study are also being utilized by colleagues for animal instillation experiments.

Experimental results on the mass and compositions of particles between 0.03 and >20 μm in aerodynamic diameter show that PM from the combustion of these fuels produces distinctive bimodal and trimodal PSDs, with a fine mode dominated by vaporization, nucleation, and growth processes. Depending on the fuel and combustion equipment, the coarse mode is composed primarily of unburned carbon char and associated inherent trace elements (fuel oil) and fragments of inorganic (largely calcium-alumino-silicate) fly ash including trace elements (coal). The three coals also produced a central mode between 0.8- and 2.0-μm aerodynamic diameter. However, the origins of these particles are less clear because vapor-to-particle growth processes are unlikely to produce particles this large.

Possible mechanisms include the liberation of micron-scale mineral inclusions during char fragmentation and burnout and indicates that refractory transition metals can contribute to PM <2.5 μm without passing through a vapor phase. When burned most efficiently, the residual fuel oil produces a PSD composed almost exclusively of an ultrafine mode (~0.1 μm). The transition metals associated with these emissions are composed of water-soluble metal sulfates. In contrast, the transition metals associated with coal combustion are not significantly enriched in PM <2.5 μm and are significantly less soluble, likely because of their association with the mineral constituents. These results may have implications regarding health effects associated with exposure to these particles.     

Real-World In-Use Activity,Fuel Use,and Emissions for Nonroad Construction Vehicles: A Case Study for Excavators

Abstract

A study design was developed and demonstrated for deployment of a portable emission measurement system (PEMS) for excavators. Excavators are among the most commonly used vehicles in construction activities. The PEMS measured nitric oxide, carbon monoxide, hydrocarbons, carbon dioxide, and opacity-based particulate matter. Data collection, screening, processing, and analysis protocols were developed to assure data quality and to quantify variability in vehicle fuel consumption and emissions rates. The development of data collection procedures was based on securing the PEMS while avoiding disruption to normal vehicle operations. As a result of quality assurance, approximately 90% of the attempted measurements resulted in valid data. On the basis of field data collected for three excavators, an average of 50% of the total nitric oxide emissions was associated with 29% of the time of operation, during which the average engine speed and manifold absolute pressure were significantly higher than corresponding averages for all data. Mass per time emission rates during non-idle modes (i.e., moving and using bucket) were on average 7 times greater than for the idle mode. Differences in normalized average rates were influenced more by intercycle differences than intervehicle differences. This study demonstrates the importance of accounting for intercycle variability in real-world in-use emissions to develop more accurate emission inventories. The data collection and analysis methodology demonstrated here is recommended for application to more vehicles to better characterize real-world vehicle activity, fuel use, and emissions for nonroad construction equipment.     

Field Measurements of Particulate Matter Emissions,Carbon Monoxide,and Exhaust Opacity from Heavy-Duty Diesel Vehicles

ABSTRACT

Diesel particulate matter (PM) is a significant contributor to ambient air PM₁₀ and PM_2.5 particulate levels. In addition, recent literature argues that submicron diesel PM is a pulmonary health hazard. There is difficulty in attributing PM emissions to specific operating modes of a diesel engine, although it is acknowledged that PM production rises dramatically with load and that high PM emissions occur during rapid load increases on turbocharged engines. Snap-acceleration tests generally identify PM associated with rapid transient operating conditions, but not with high load. To quantify the origin of PM during transient engine operation, continuous opacity measurements have been made using a Wager 650CP full flow exhaust opacity meter. Opacity measurements were taken while the vehicles were operated over transient driving cycles on a chassis dynamometer using the West Virginia University (WVU) Transportable Heavy Duty Vehicle Emissions Testing Laboratories. Data were gathered from Detroit Diesel, Cummins, Caterpillar, and Navistar heavy-duty (HD) diesel engines. Driving cycles used were the Central Business District (CBD) cycle, the WVU 5-Peak Truck cycle, the WVU 5-Mile route, and the New York City Bus (NYCB) cycle. Continuous opacity measurements, integrated over the entire driving cycle, were compared to total integrated PM mass. In addition, the truck was subjected to repeat snap-acceleration tests, and PM was collected for a composite of these snap-acceleration tests. Additional data were obtained from a fleet of 1996 New Flyer buses in Flint, MI, equipped with electronically controlled Detroit Diesel Series 50 engines. Again, continuous opacity, regulated gaseous emissions, and PM were measured. The relationship between continuous carbon monoxide (CO) emissions and continuous opacity was noted. In identifying the level of PM emissions in transient diesel engine operation, it is suggested that CO emissions may prove to be a useful indicator and may be used to apportion total PM on a continuous basis over a transient cycle. The projected continuous PM data will prove valuable in future mobile source inventory prediction.     

Effects of Fuel Type,Driving Cycle,and Emission Status on In-Use Vehicle Exhaust Reactivity

ABSTRACT

The introduction of reformulated gasolines significantly reduced exhaust hydrocarbon (HC) mass emissions, but few data are available concerning how these new fuels affect exhaust reactivity. Similarly, while it is well established that high-emitting vehicles contribute a significant portion of total mobile source HC mass emissions, it is also important to evaluate the exhaust reactivity from these vehicles. The objective of this study was to evaluate the relative influence on in-use vehicle exhaust reactivity of three critical factors: fuel, driving cycle, and vehicle emission status. Nineteen in-use vehicles were tested with seven randomly assigned fuel types and two driving cycles: the Federal Test Procedure (FTP) and the Unified Cycle (UC). Total exhaust reactivity was not statistically different between the FTP and UC cycles but was significantly affected by fuel type. On average, the exhaust reactivity for California Phase 2 fuel was the lowest (16 % below the highest fuel type) among the seven fuels tested for cold start emissions. The average exhaust reactivity for high-emitting vehicles was significantly higher for hot stabilized (11%) and hot start (15%) emissions than for low-emitting vehicles. The exhaust reactivities for the FTP and UC cycles for light-end HCs and carbonyls were significantly different for the hot stabilized mode. There was a significant fuel effect on the mean specific reactivity (SR) for the mid-range HCs, but not for light-end HCs or carbonyls, while vehicle emission status affected the mean SR for all three HC compound classes.     

Electricity from Fossil Fuels without CO2 Emissions: Assessing the Costs of Carbon Dioxide Capture and Sequestration in U.S. Electricity Markets

ABSTRACT

The decoupling of fossil-fueled electricity production from atmospheric CO₂ emissions via CO₂ capture and sequestration (CCS) is increasingly regarded as an important means of mitigating climate change at a reasonable cost. Engineering analyses of CO₂ mitigation typically compare the cost of electricity for a base generation technology to that for a similar plant with CO₂ capture and then compute the carbon emissions mitigated per unit of cost. It can be hard to interpret mitigation cost estimates from this plant-level approach when a consistent base technology cannot be identified. In addition, neither engineering analyses nor general equilibrium models can capture the economics of plant dispatch. A realistic assessment of the costs of carbon sequestration as an emissions abatement strategy in the electric sector therefore requires a systems-level analysis. We discuss various frameworks for computing mitigation costs and introduce a simplified model of electric sector planning. Results from a “bottom-up” engineering-economic analysis for a representative U.S. North American Electric Reliability Council (NERC) region illustrate how the penetration of CCS technologies and the dispatch of generating units vary with the price of carbon emissions and thereby determine the relationship between mitigation cost and emissions reduction.     

Emissions tradeoffs among alternative marine fuels: total fuel cycle analysis of residual oil, marine gas oil, and marine diesel oil

Worldwide concerns about sulfur oxide (SOx) emissions from ships are motivating the replacement of marine residual oil (RO) with cleaner, lower-sulfur fuels, such as marine gas oil (MGO) and marine diesel oil (MDO). Vessel operators can use MGO and MDO directly or blended with RO to achieve environmental and economic objectives. Although expected to be much cleaner in terms of criteria pollutants, these fuels require additional energy in the upstream stages of the fuel cycle (i.e., fuel processing and refining), and thus raise questions about the net impacts on greenhouse gas emissions (primarily carbon dioxide [CO2]) because of production and use. This paper applies the Total Energy and Environmental Analysis for Marine Systems (TEAMS) model to conduct a total fuel cycle analysis of RO, MGO, MDO, and associated blends for a typical container ship. MGO and MDO blends achieve significant (70-85%) SOx emissions reductions compared with RO across a range of fuel quality and refining efficiency assumptions. We estimate CO2 increases of less than 1% using best estimates of fuel quality and refinery efficiency parameters and demonstrate how these results vary based on parameter assumptions. Our analysis suggests that product refining efficiency influences the CO2 tradeoff more than differences in the physical and energy parameters of the alternative fuels, suggesting that modest increases in CO2 could be offset by efficiency improvements at some refineries. Our results help resolve conflicting estimates of greenhouse gas tradeoffs associated with fuel switching and other emissions control policies.     

Sensitivity Analysis and Evaluation of MicroFacCO: A Microscale Motor Vehicle Emission Factor Model for CO Emissions

ABSTRACT

This paper presents a sensitivity analysis of a microscale emission factor model (MicroFacCO) for predicting realtime site-specific motor vehicle CO emissions to input variables, as well as a limited field study evaluation of the model. The sensitivity analysis has shown that MicroFacCO emission estimates are very sensitive to vehicle fleet composition, speed, and ambient temperature. For the present U.S. traffic fleet, the CO emission rate (g/mi) is increased by more than 500% at 5 mph in comparison with a speed greater than 40 mph and by ~67% at ambient temperatures of 45 °F and ≥95 °F in comparison with an ambient temperature of 75 °F.     

Biofilter Treatment of Volatile Organic Compound Emissions from Reformulated Paint: Complex Mixtures,Intermittent Operation,and Startup

Abstract

Two biofilters were operated to treat a waste gas stream intended to simulate off-gases generated during the manufacture of reformulated paint. The model waste gas stream consisted of a five-component solvent mixture containing acetone (450 ppm_v), methyl ethyl ketone (12 ppm_v), toluene (29 ppm_v), ethylbenzene (10 ppm_v), and p-xylene (10 ppm_v). The two biofilters, identical in construction and packed with a polyurethane foam support medium, were inoculated with an enrichment culture derived from compost and then subjected to different loading conditions during the startup phase of operation. One biofilter was subjected to intermittent loading conditions with contaminants supplied only 8 hr/day to simulate loading conditions expected at facilities where manufacturing operations are discontinuous. The other biofilter was subjected to continuous contaminant loading during the initial start period, and then was switched to intermittent loading conditions. Experimental results demonstrate that both startup strategies can ultimately achieve high contaminant removal efficiency (>99%) at a target contaminant mass loading rate of 80.3 g m^?3 hr^?1 and an empty bed residence time of 59 sec. The biofilter subjected to intermittent loading conditions at startup, however, took considerably longer to reach high performance. In both biofilters, ketone components (acetone and methyl ethyl ketone) were more rapidly degraded than aromatic hydrocarbons (toluene, ethylbenzene, and p-xylene). Scanning electron microscopy and plate count data revealed that fungi, as well as bacteria, populated the biofilters.     

The effects of Orimulsion and Fuel Oil #6 on the hatching success of copepod resting eggs in the seabed of Tampa Bay,Florida

A 3-month microcosm study was conducted to observe the potential effects of two fuels, Orimulsion and Fuel Oil #6, on the hatching success of copepod resting eggs in the seabed of Tampa Bay, Florida. Microcosms were dosed with one of five hydrocarbon treatments via hydrocarbon-coated sand and compared with controls. Acartia tonsa eggs were nonviable in all treatments after only a few weeks of incubation, as evidenced by a marked decline in the abundance of nauplii. However, there was no evidence that exposure to simulated spills of 700 or 7000 ppm of either fuel led to significant increases in resting egg mortality as compared with controls. The results further indicate that, regardless of environmental conditions, resting eggs of A. tonsa do not remain viable in the sediment for extended periods of time.