Abstract
ABSTRACT This paper presents a comprehensive set of ultrafine particles (UFPs) emission factors (EFs) for heavy duty vehicles (HDVs) as a function of vehicle flow rate, speed, and mode of operation (free flow and congestion) using 664 measurements of UFPs, carbon dioxide (CO2), meteorology and traffic conditions near a major roadway (average daily traffic 300,000 day–1). 5-min samples were collected for 2 to 3 hour time period on 60 days between 2015 and 2018. The average traffic-induced concentration of UFPs was 11,300 pt cm–3 for free flow and 12,400 pt cm–3 for congestion. Results demonstrate that HDVs produce significantly more dispersion (30x) than light duty vehicles (LDVs). The additional dispersion from HDVs results in the minimum pollutant concentrations occurring at the highest vehicle flow rate. EFs for UFPs are determined using inverse modeling based on the calculated CO2 dispersion. This eliminates the need to rely on air-quality models to estimate dispersion. The EFs for HDVs range from 4 × 1014 to 20 × 1014 (pt km–1 veh–1). The variations in EFs are correlated with variations in vehicle flow rate and speed. The average UFP EFs for HDVs are significantly higher (3x) for congestion compared to free flow. UFP EFs for HDVs are more sensitive to speed in congestion compare to in free flow conditions. Thus, even a moderate increase in HDVs speed or mitigation of congestion will have a significant impact on lowering UFP concentrations.
Highlights
Vehicle emissions are one of the main sources of urban air pollution and exposure to vehicle emissions have been associated with negative health effects
This paper presents near roadway light-duty vehicle (LDV) dispersion and ultrafine-particle (UFP) emission factors (EFs) as a function of vehicle flow rate, speed and mode of operation using 300 5-min measurements of carbon dioxide (CO2), ultrafine particles (UFPs), meteorology and traffic conditions near a LDV only roadway
The UFP EFs varied from 0.5 × 1013 to 1.5 × 1013 pt km–1 veh–1 for LDV (3x)
Summary
Vehicle emissions are one of the main sources of urban air pollution and exposure to vehicle emissions have been associated with negative health effects. There are two dispersion models that have been widely used, California Line Source Dispersion Model (CALINE4) (Benson, 1992) and AMS/EPA Regulatory Model (AERMOD) (Cimorelli et al, 2005). Both models assume that the vehicle emissions and turbulence are uniform across the road. AERMOD is an atmospheric dispersion model developed by the American Meteorology Society and EPA for application to most types of pollutant sources. AERMOD treats the line source as an area (or volume) source
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