Sheng Xiang, Yu Ting Yu, Zhice Hu, Kenneth E. Noll 

Department of Civil, Architecture and Environmental Engineering, Illinois Institute of Technology, Chicago, IL 60616, USA

Received: August 9, 2019
Revised: October 16, 2019
Accepted: October 19, 2019
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Cite this article:
Xiang, S., Yu, Y.T., Hu, Z. and Noll, K.E. (2019). Characterization of Dispersion and Ultrafine-particle Emission Factors Based on Near-roadway Monitoring Part II: Heavy Duty Vehicles. Aerosol Air Qual. Res. 19: 2421-2431.


  • CO2 and UFP concentrations were measured near a roadway with both LDVs and HDVs.
  • Ratio of HDV/LDV dispersion varied between 25 and 40 depending on traffic conditions.
  • Increase in dispersion due to HDVs provided added dispersion for vehicle emissions.
  • Lowest pollutant concentrations occurred at the maximum vehicle flow rate.



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.

Keywords: Air quality monitoring; Ultrafine particle; Dispersion; Heavy-duty vehicle emission; Free flow and congestion.

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