Fine Particle (Nanoparticle) Emissions on Minnesota Highways

Status:  Complete
Report Date:  11/28/2001


This study examined the physical characteristics of combustion aerosols found on Minnesota highways. It emphasized the characterization of nanoparticles (less than 50 nm) with the goal of providing real-world data for the development of engine laboratory test methods. On-road particulate matter emissions ranged between 104 to 106 particles/cm3 with the majority of the particles by number being less than 50 nm in diameter. High-speed traffic produced high nanoparticle number concentrations, and diesel traffic further increased number concentrations. At high vehicular speeds, particulate matter emissions increase because of higher engine load and fuel consumption. Measurements made at speeds less than 20 miles per hour showed lower number but higher volume concentrations and larger particles. Measurements made 10-30 m from the highway in residential areas approached on-road concentrations with similar size distributions and high concentrations of nanoparticles. Lower concentrations and larger particles were observed in residential areas from 500 to 700 m from the highway. Researchers estimated fuel specific and particle/mi emission rates from data collected on two different days. The particle/mi emissions were greater than published figures but mass emission rates compared well with published values. However, colder temperatures, different dilution, and sampling conditions and different instrumentation could explain the increased estimates.

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