On-Road Source Apportionment Studies
Johnson, J. P., D. B. Kittelson, W. F. Watts, Jr. 2009.
The Effect of Federal Fuel Sulfur Regulations on In-Use Fleets: On-Road Heavy-Duty Source Apportionment.Environ. Science & Technol, 43(14):5358-5364. Link To Paper
AbstractFrom 2002 to 2007 fuel sulfur content in the Minneapolis/St. Paul area decreased from about 325 ppm S to < 15 ppm S as a result of EPA regulations. We hypothesized that the reduction in fuel sulfur would result in a reduction of fuel specific heavy duty (HD) particle number emissions for the on-road diesel fleet. Fuel specific emissions were estimated by collecting on-road aerosol data, and exploiting the difference in the relative volumes of HD and light duty (LD) traffic on the roadway.
Fuel-specific particle number emissions for HD vehicles were measured to be 9.1±6.6×1015 and 3.2±2.8×1015 particles/kg of fuel burned, in 2006 and 2007, respectively, a reduction of 65%. In an earlier study in 2002 particle number emissions for the in-use HD fleet were 4.2±0.6×1015 particles/km compared to the current measurements of 2.8±2.1×1015 and 9.9±8.7×1014 particles/km in 2006 and 2007, respectively. The HD particle mass emission standard remained unchanged from 1994 through 2006 and few 2007 HD vehicles were on the road at the time of this study so the decreases in number observed emissions are more likely due to reductions in the sulfur content of the fuel than to changes in engine and aftertreatment design
Johnson, J. P., D. B. Kittelson, W. F. Watts, 2005.
Source Apportionment of Diesel and Spark Ignition Exhaust Aerosol Using On-Road Data from the Minneapolis, Metropolitan Area.Atmos. Environ. 39(11):2111-2121. Link To Paper
AbstractAir quality measurements were made on interstate highways in the Minneapolis metropolitan area. Gas and aerosol concentrations were measured on weekdays and weekends. By exploiting the difference in the relative volumes of heavy duty (HD) Diesel and light duty (LD) spark ignition (SI) vehicles on weekdays and weekends, we were able to estimate apportioned fuel specific emissions.
The on-road, apportioned, fuel-specific particle number emissions factors, estimated from Condensation Particle Counter (CPC) measurements were 1.34 ± 0.2 x 1016 particles kg-1 for Diesels and 7.1 ± 1.6 x 1015 particles kg-1 for spark ignition vehicles. Estimates from the Scanning Mobility Particle Sizer (SMPS) measurements were 2.1 ± 0.3 x 1015 particles kg-1 for Diesels and 3.9 ± 0.6 x 1014 particles kg-1 for SI vehicles. The difference between CPC and SMPS measurements is mainly due to different lower size detection limits of the instruments, ~3 and ~10 nm, respectively.
On a weekly weighted basis and on weekdays, the majority of particle number was attributed to HD Diesel traffic. Weekend production of particles can be primarily attributed to light duty SI automobiles. On a per vehicle basis, HD vehicles produced substantially greater numbers of particles. On a fuel specific basis, HD vehicles produce slightly higher concentrations of particles than light duty vehicles. The relative contribution of LD vehicles to particle number emissions increased as particle size decreased.
The HD apportioned size distributions were similar to size distributions measured during other on-road and laboratory studies. The LD apportioned size distribution was bounded by laboratory and on-road size distributions. Our work is representative of summer, highway cruise conditions. It is likely that under cold start and high load operating conditions LD emissions will increase relative to HD emissions.
Kittelson, D. B., W. F. Watts and J. P. Johnson. 2004.
Nanoparticle Emissions on Minnesota Highways.Atmos. Environ. 38:9-19. Link to Paper
AbstractThe objective of this project was to characterize on-road aerosol on highways surrounding the Minneapolis area. Data were collected under varying on-road traffic conditions and in residential areas to determine the impact of highway traffic on air quality. The study was focused on determining on-road nanoparticle concentrations, and estimating fuel-specific and particle emissions km-1.
On-road aerosol number concentrations ranged from 104 to 106 particles cm -3. The highest nanoparticle concentrations were associated with high-speed traffic. At high vehicular speeds engine load, exhaust temperature, and exhaust flow all increase resulting in higher emissions. Less variation was observed in particle volume, a surrogate measure of particle mass. Most of the particles added by the on-road fleet were below 50 nm in diameter. Particles in this size range may dominate particle number, but contribute little to particle volume or mass. Furthermore, particle number is strongly influenced by nucleation and coagulation, which have little or no effect on particle volume. Measurements made in heavy traffic, speeds < 32 km hr-1, produced lower number concentrations and larger particles.
Number concentrations measured in residential areas, 10-20 m from the highway, were considerably lower than on-road concentrations, but the size distributions were similar to on-road aerosol with high concentrations of very small (<20 nm) particles. Much lower number concentrations and larger particles were observed in residential areas located 500 to 700 m from the highway.
Estimated emissions of total particle number larger than 3 nm ranged from 1.9-9.9 x 1014 particles km-1 and 2.2-11 x 1015 particles (kg fuel)-1 for a gasoline-dominated vehicle fleet.
Kittelson, D, B., W. F. Watts and J. P. Johnson. 2001.
Fine Particle (Nanoparticle) Emissions on Minnesota Highways.Mn/DOT Report No. 2001-12, 87 pp. Link to Paper
AbstractThis 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 mph 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 500 to 700 m from the highway.
Fuel specific and particle/mi emission rates were estimated from data collected on two different days. The particle/mi emissions were about an order of magnitude 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 our increased estimates.