Implications of Measured In-Use Light Duty Gasoline Vehicle Emissions for Emission Inventory Development at High Spatial and Temporal Resolution

The objective here is to evaluate the intra-and inter-vehicle variability in realworld light-duty gasoline vehicle emissions and assess implications for development of onroad vehicle emission inventories. A field study was conducted to characterize variability for selected vehicles for both total emissions and emission rates by routes, time of day, road grade, and among vehicles. Real-world data were collected using a portable emission measurement system (PEMS). The study area included two origin/destination pairs, each with three alternative routes. On an average trip basis, the total NO emissions differed by 24% when comparing alternative routes and increased by 19% when comparing congested versus less congested travel time periods. Positive road grades were associated with approximately a 20 percent increase in localized emissions rates, while negative road grades were associated with a similar relative decrease. The average NO vehicle-specific power based modal emission rates differed by more than 2 orders of magnitude when comparing different vehicles. The results demonstrate that alternative routing can significantly impact trip emissions. Road grade should be taken into account for localized emissions estimation. Furthermore, there are locations on the roadway network where one or more vehicles may have high proportions of its total trip emissions. The magnitude and location of these emissions hotspots can vary by vehicle, pollutant, and time of day. Micro-scale modeling may be needed to capture episodic emissions such as for near-road short-term human exposure assessment. Implications for emission inventory development are discussed.