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Weekly UpdatesABSTRACT
The Coordinating Research Council, Inc. (CRC) held its 17th On-Road Vehicle Emissions Workshop in March 2007, where results of the most recent on-road vehicle emissions research were presented. We summarize ongoing work from researchers who are engaged in improving our understanding of the role and contribution of mobile sources to ambient air quality and emission inventories. Participants in the Workshop discussed efforts to improve mobile source emission models, light- and heavy-duty vehicle emissions measurements, on-and off-road emissions measurements, effects of fuels and lubricating oils on emissions, as well as emerging issues and topics for future research.
INTRODUCTION
The 17th Coordinating Research Council Inc. (CRC) On-Road Vehicle Emissions Workshop was held March 26-28, 2007, in San Diego, CA. These workshops, which began in 1990, provide a forum for presenting and discussing the most recent results on improving our understanding of the role and contribution of mobile sources to air quality. More than 200 representatives from Austria, Belgium, Canada, China, Denmark, Finland, Japan, Korea, Portugal, Sweden, the United Kingdom, and the United States representing industry, government, academia, and consulting groups took part in the Workshop. The objectives of the Workshop were to present the most recent results from research on:
* Emission modeling;
* On-road gasoline and diesel vehicle emissions;
* Off-road emissions;
* Fuel effects on vehicle emissions;
* Measurement methods;
* Particulate matter emissions;
* Portable emission monitoring systems; and
* Emission control measures.
There were 60 presentations in nine sessions, 29 displays in poster sessions, and 8 equipment demonstrations during the Workshop. Brent Bailey, Chris Tennant, and the CRC staff, with Steven Cadle of General Motors (GM) and Mani Natarajan of Marathon Petroleum serving as Workshop co-chairmen, provided Workshop coordination. Robert Sawyer, who at the time was Chairman of the California Air Resources Board (CARB), was the keynote speaker at the Workshop. Session chairs were Fred Minassian of the South Coast Air Quality Management District (SCAQMD), John Koupal of the U.S. Environmental Protection Agency (EPA), Alberto Ayala of CARB, Rob Graze of Caterpillar, Inc., Mani Natarajan, Kevin Black of the Federal Highway Administration (FHWA), Chris Tennant, Hannah Murray from Toyota, and Doug Lawson of the National Renewable Energy Laboratory (NREL).
The complete Workshop proceedings are available from CRC Inc., 3650 Mansell Road, Suite 140, Alpharetta, GA 30022; phone: 678-795-0506; fax: 678-795-0509; e-mail: jantucker@crcao.org. This paper summarizes presentations given in each session at the Workshop. Summaries of the CRC workshops have been published in the Journal of the Air & Waste Management Association; the three most recent summaries are found in Vol. 55, pp 130-146, Vol. 56, pp 121-136, and Vol. 57, pp 139-145.
In addition to the technical papers and posters presented at the Workshop, several vendors provided on-site demonstrations of mobile laboratory and emissions measurement equipment.
EMISSION MODELING
New research compared and contrasted methods for generating emission inventories using a fuel sales-based approach versus a vehicle-miles-traveled (VMT) approach. The VMT-based methods were reported to be more robust for emission inventory development because of the ability to incorporate travel demand inputs; however, it is recommended that future application should combine the merits of both approaches.
A demonstration version of EPA's Motor Vehicle Emission Simulator (MOVES) model was released in spring 2007, with a draft version of the full on-road model scheduled for release in 2008. Light-duty (LD) exhaust hydrocarbons (HCs), carbon monoxide (CO), and nitrogen oxides (N[O.sub.x]) emissions data from inspection and maintenance (inspection and maintenance [I/M]) programs or I/M program assessments in several cities are being evaluated for suitability to provide MOVES emission rates. Research on estimates of particulate matter (PM) emissions from brake wear is focusing on new methods to better account for braking severity and to allocate brake emissions to braking events using the MOVES modal approach.
CARB plans to build a toolbox of mobile source emissions models that might include: (1) its EMFAC model for statewide and regional inventory development, (2) a link-based model for corridor and subregional analyses, and (3) a modal model to estimate emissions at the local scale. A link-level model is under development that integrates emission rates from EMFAC with travel demand model activity. CARB is also evaluating modal emission models including MOVES (EPA), Heavy Heavy-Duty Diesel Vehicle Mobile Emissions Model (HHDDV-MEM; Georgia Tech) and Comprehensive Mobile Emission model (CMEM; University of California at Riverside). CARB staff have studied N[O.sub.x] emissions from heavy-duty (HD) trucks, finding that emissions vary between modal and EMFAC models from -80 to +180% and -80 to +100%, depending on-road type. They found that each model estimates fewer emissions on negative road grades than positive road grades for all five driving cycles, with the HHDDV-MEM and CMEM models being more sensitive to road grade than MOVES.
CARB is also improving estimates of emissions from HD truck goods movement by breaking out fleet and activity characteristics of trucks for three types of activities in California: in-state hauls, interstate hauls conducted by California registered trucks, and interstate hauls conducted by non-California trucks. CARB is also updating their OFFROAD model to include spatial and temporal features for improved accuracy.
Research is being conducted that models fuel consumption and/or emissions on the basis of a vehicle specific power (VSP) approach. One effort focused on fuel consumption for transit buses in the United States and Portugal, including a prototype hydrogen fuel cell bus--under real-world operating conditions absolute errors between trip fuel consumption estimates and actual fuel use were generally under 10%. Another effort evaluated modeling approaches to developing vehicle-specific microscale fuel use and emissions rate models on the basis of portable emission measurement systems (PEMS), finding that these models typically produced relatively greater variations than MOBILE6. A third effort quantified modal emission rates for a selected hybrid vehicle under hot-stabilized conditions using VSP-based modal average fuel consumption rates estimated using a dynamometer database. Evaluation of model predictions for when the hybrid engine is running demonstrates close agreement between the model and the independent evaluation data.
A project conducted in the Atlanta area recorded license plate data from five highway locations during the morning rush hour to improve the characterization of Atlanta's vehicle fleet composition. Once completed, the revised fleet composition estimates will be input into the MOBILE model to observe the changes in emissions outputs relative to national default estimates.
GASOLINE VEHICLE EMISSIONS AND EMISSION INVENTORY
Emissions from gasoline engines contribute a significant amount to current urban emission inventories, even though new vehicles' emissions are extremely low. High-emitting vehicles are significant contributors to on-road gasoline emissions. In warm, stable operating conditions, a single high emitter can produce mobile source air toxic emissions equivalent to approximately 1000 new vehicles. Tunnel studies continue to be a reliable way to measure on-road vehicle emissions under hot-stabilized operating conditions. Between 1997 and 2007, vehicle emissions measured in California's Caldecott Tunnel showed vast reductions from the LD and HD fleets: N[O.sub.x] emission reductions of 67 and 27%, respectively, whereas [PM.sub.2.5] emissions were reduced 36 and 56%, respectively.
A multiyear remote sensing program sponsored by CRC has reported decreasing on-road HC and CO emissions, with the highest 1% of the fleet producing at least 25% of the measured HC and CO on-road fleet emissions. Measurements were made at fixed locations in several cities. Deterioration rates appear to be much lower than those used in MOBILE. Engine lubricating oil is receiving additional scrutiny as a producer of mobile source emissions. Recent work has identified the role of lubricating oil in producing PM emissions, but the role of fuel versus lubricating oil in producing PM and semivolatile emissions needs to be better understood. Hopanes, steranes, and polycyclic aromatic hydrocarbons (PAH) can serve as markers of lubricating oil and fuels in quantifying their influence on emissions.
Environment Canada has evaluated hybrid vehicle emissions at 20 and -18[degrees]C, reporting significantly higher CO and nonmethane HC levels at lower vehicle operating temperatures. N[O.sub.x] also increased slightly at cold temperatures, but not as significantly; however, the hybrids at lower temperatures are still relatively clean. For example, the vehicles at 20[degrees]C still emitted less CO than the EPA Tier 2 Bin 3 full useful-life vehicle standard.
An area of continuing research is evaporative or nontailpipe emissions and their contribution to emission inventories. Future inventories predict that non-tailpipe HC emissions will contribute roughly half of the total HC emissions from on-road mobile sources. CRC and EPA continue to sponsor projects that characterize evaporative emission rates and mechanisms. The goal is to characterize the relative importance of emissions from leaks, fuel vapor venting (from diurnal temperature changes), and permeation losses. There is a need to properly evaluate non-tailpipe HC emissions, given that near-zero evaporative emissions are required from 2004 and later model year vehicles.
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