1. Vehicle generated nanoparticles are not an artifact! D. B. Kittelson, W.F. Watts, and J.P. Johnson Center for Diesel Research University of Minnesota 8th CONFERENCE ON ENVIRONMENTAL SCIENCE AND TECHNOLOGY PARTICULATES WORKSHOP 11th SEPTEMBER 2003 Lemnos Island, GREECE

2. Outline Size and composition On-road measurements –On-road measurements in mixed urban traffic –Weekday/weekend determinations of on-road emission factors –On-road characterization of post 2007 system Conclusions

3. Typical Engine Exhaust Particle Size Distributions, Number, Surface Area, and Mass Weightings Are Shown

4. Nuclei mode (~3 to 30 nm diameter) The nuclei mode contains most of the particle number Nuclei mode particles form mainly from volatile precursors 1 –The nuclei mode typically consists mainly of heavy hydrocarbons, mainly from lubricating oil, and sulfates –Although although the mode is mainly hydrocarbon, its formation is facilitated by sulfur in the fuel –Its formation is very dependent on dilution conditions, especially dilution rate and dilution air temperature –Its formation is favored by low solid carbon and high precursor concentration Solid nuclei mode particles may form from metals in the lube oil or fuel –Formed from oil under engine conditions that lead to little solid carbon formation. –Formed from fuel when metallic additives or high metal fuels are used. A volatile nuclei mode will be all that is left when solid particles are removed by exhaust filtration 1 - Sakurai, Hiromu, Herbert J. Tobias, Kihong Park, Darrick Zarling, Kenneth S. Docherty, David B. Kittelson, Peter H. McMurry, and Paul J. Ziemann, 2002. “On-Line Measurements of Diesel Nanoparticle Composition, Volatility, and Hygroscopicity,” Submitted to Atmospheric Environment

5. Accumulation mode (~30 to 500 nm) The accumulation mode contains most of the particle mass and “soot” Consists primarily of carbonaceous agglomerates and adsorbed OC Particles in this mode are strongly light absorbing and may influence global warming Most of the lubricating oil ash is found in this mode – this enhances soot oxidation in exhaust filters but eventually plugs them Density of accumulation mode particles decreases with increasing size 1 –Fractal like behavior –Low densities cause size to be underestimated by some methods Accumulation mode particles have been reduced sharply by better engine technology and will be eliminated by efficient filtration 1 - Park, Kihong, Feng Cao, David B. Kittelson, and Peter H. McMurry, 2002. “Relationship Between Particle Mass and Mobility, and Between Aerodynamic and Mobility Size Distributions for Diesel Exhaust Particles,” Submitted to Environmental Science & Technology

6. U of M Mobile Laboratory built to study formation of nanoparticles in the atmosphere for the CRC E-43 project Instruments (primary instruments highlighted in blue) –SMPS to size particles in 9 to 300 nm size range –ELPI to size particles in 30 to 2500 nm size range –CPC to count all particles larger than 3 nm –Diffusion Charger to measure total submicron particle surface area –Epiphaniometer to measure total submicron particle surface area –PAS to measure total submicron surface bound PAH equivalent –CO 2, CO, and NO analyzers for gas and dilution ratio determinations

7. On-highway measurements made on urban freeways in Minnesota show a large nuclei mode even in the absence of significant Diesel traffic Traffic speed has at least as much influence on the size of the nuclei mode as the presence of Diesel traffic Particle number increases and size decreases as traffic speed increases Particle volume (mass) is higher under low speed congested conditions It appears that slow moving congested traffic leads to storage of volatile materials in the exhaust system As vehicles speed up the exhaust system heats leading to the release of the materials which subsequently form nanoparticles Diesel No Diesel

8. Nuclei Mode Decays Rapidly Downwind of Roadways Modeling (Capaldo and Pandis, 2001) indicates –For typical urban conditions, characteristic times and transit distances for 90 % reduction of ultrafine concentrations are on the order of a few minutes and 100-1000 m, respectively. –For a given wind speed, ultrafine particles are expected to survive and travel a factor of ten greater distances in a rural flat area as compared to an urban downtown location. Mobile particle sources will influence the aerosol particle number concentrations mainly near roadways.

9. Nanoparticles Are Composed of Mainly Volatile Material 87-95% Reduction

10. On-Road Characterization of Real World Fleets: Weekday / Weekend On-Highway Apportionment Experiments Summertime urban freeway measurements Over-the-road aerosol, corrected for the background is contributed by vehicles in proportion to their traffic volume. Measuring traffic volumes and aerosol concentrations on days with differing SI to Diesel ratios gives a system of equations that can be solved for average Diesel and SI contribution on a per unit traffic volume basis Presented on a fuel specific (per kg of fuel) basis Principal uncertainties are in traffic counts and background corrections

11. Diesel/SI Ratio By Route And Day Route selected

12. Average Weekend vs. Weekday Size Distributions

13. Diesel and SI Apportioned Size Distributions on a Fuel Specific Basis

14. Diesel On-Highway Compared to CRC E-43 Fleet Average On a Fuel Specific Basis

15. Source Apportioned Highway Cruise SI Fleet Average Compared to Chase and Chassis Dyno Measurements

16. The proposed (by Swiss) EU standard of 10 11 particles/km corresponds to about 2 x 10 12 particles/kg fuel of solid particles If we assume all particles above 30 nm are solid our fleet emission factors are 5 x 10 14 and 9 x 10 13 particles/kg fuel for Diesel and SI, respectively These are a snapshot of Minnesota urban freeway fleets – more work is needed Fuel Specific Emissions – Diesel and SI Summertime Highway Cruise Dp > 3 nmDp > 10 nm

17. On-road characterization of post a 2007 aftertreatment system – we sniff our own exhaust plume Driver side sample point Passenger side sample point Background sample point Stacks

18. On road tests of particle filtration device – volume (mass) distributions Engine out with low S oil Filter with standard oil, August Filter with standard oil, October All tests done with 15 ppm S fuel (post 2006) with standard or low sulfur lubricant

19. On-road nanoparticle measurements for real world fleets On-road nanoparticles are real On-road submicron on-road aerosols are found in two principal size modes –A nuclei mode in the nanoparticle range containing most of the particle number –An accumulation mode in the ultrafine and fine range containing most of the particle mass. Most nuclei mode particles are volatile and very sensitive to dilution conditions, both on-road and in the laboratory Both Diesel and SI engines are important contributors to the on-road aerosol –Both engine types produce significant nuclei mode (nanoparticles) –SI particles are usually smaller –SI particle emissions are much more load dependent On-road measurements with post 2007 systems may show large nuclei mode with some systems More work should be done to determine nanoparticle formation with new engines and fuels and for a range of ambient and operating conditions

20. Acknowledgements We have had help from many collaborators –In the Center for Diesel Research Feng Cao, Marcus Drayton, Jason Johnson, Hee Jung Jung, Duane Paulsen, Winthrop Watts, Robert Waytulonis, Qiang Wei, Darrick Zarling –At Paul Scherrer Institute Nick Bukowiecki, Urs Baltensperger, Adelheid Kasper And many sponsors –Coordinating Research Council, U.S. Office of Heavy Vehicle Technologies, Engine Manufacturers Association, Southcoast Air Quality Management District, California Air Resources Board, BP/Amoco, Castrol, Corning, Cummins, Caterpillar, Perkins, and Volvo.