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NARSTO Workshop on Innovative Methods for Emission Inventory Development and Evaluation University of Texas, Austin October 14-17, 2003 |
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Temporal Patterns in Nitrogen Oxide Emissions from Diesel Engines
Robert Harley
Department of Civil and Environmental Engineering, University of California at Berkeley
A fuel-based approach to estimating on-road diesel engine exhaust emissions will be described that relies on fuel sales rather than distance traveled. Changes in NOx emissions between 1990 and 2000 are assessed. Diesel exhaust is now the dominant mobile source of NOx emissions. While NOx emissions from gasoline-powered passenger vehicles decreased during the last decade, emissions from diesel engines increased in both relative and absolute terms. This state of affairs is due to rapid growth in the total amount of diesel fuel consumed, a focus on controlling emissions from light-duty vehicles, and ineffective controls that failed to achieve intended reductions in diesel NOx emissions during the 1990s.
Weigh-in-motion traffic count data are used to define the temporal distribution of emissions on fine time scales. Compared to light-duty passenger vehicles, diesel truck traffic is found to have different temporal distributions of emissions on diurnal and weekly time scales. Large decreases in diesel truck traffic on weekends cause a significant perturbation to the NOx budget for urban areas. These changes can be an important contributor to weekday-weekend differences in photochemical air pollution.