1. Regional Modeling of The Atmospheric Fate and Transport of Benzene and Diesel Particles with CMAQ Christian Seigneur, Betty Pun Kristen Lohman, and Shiang-Yuh Wu AER San Ramon, CA

2. Acknowledgments Project A-42-1 funded by the Coordinating Research Council (CRC) and the U.S. DOE Office of FreedomCAR and Vehicle Technologies through the National Renewable Energy Laboratory (NREL)

3. Air Toxics Regional Model CMAQ –with benzene chemistry –with “diesel particles” species

4. Benzene Chemistry C 6 H 6 + OH Products k = 1.3 x 10 -12 cm 3 molec -1 s -1 at 298 K Benzene half-life of about 1 week OH concentrations from CMAQ chemistry (CBM-IV)

5. Diesel Particles A fixed bimodal distribution of diesel particles was assumed for the emitted and ambient diesel particles, with modes centering around 0.055 and 0.5  m. Dry deposition is simulated using the algorithm of Venkatram and Pleim (1999)

6. Application to the Northeast Domain: Northeastern United States Period: July 11-15, 1995 Models: 3-D nested regional model (modified CMAQ) with 12 and 4 km horizontal resolution

7. Nested Modeling Domains 47

8. Emission Inventories Benzene: National Toxics Inventory (1996) with spatial resolution by county and annual resolution Diesel particles: National Emission Inventory (1996) with spatial resolution by county and annual resolution SMOKE emission processing –surrogate files for spatial distribution (e.g., major highways, population) –temporal profiles (seasonal, weekday/weekend, diurnal) according to SCC

9. Emissions of Benzene (moles/hr)

10. Benzene Concentrations (ppm) 15 July 1995, 6 a.m., 12 km resolution

11. Benzene Concentrations (ppm) 15 July 1995, 6 a.m., 4 km resolution

12. Comparison of Simulated Urban and Rural Benzene Concentrations (ppm)

13. Benzene (ppb) Simulation vs. Measurements LocationSimulationMeasurements (1) Urban1 - 50.9 - 26 Suburban - Rural 0.1 – 0.6 Remote< 0.10.008 – 0.2 (1) Finlayson-Pitts & Pitts, 1999 0.1 - 0.5

14. Model Performance for Benzene Concentrations 12 km resolution domain 4 km resolution domain Number of data pairs 6735 Normalized error53%64% Normalized bias8%40% Correlation coefficient 0.190.50

15. Emissions of Diesel Particles (kg/hr)

16. Diesel Concentrations (  g/m 3 ) 15 July 1995, 6 a.m., 12 km resolution

17. Diesel Concentrations (  g/m 3 ) 15 July 1995, 6 a.m., 4 km resolution

18. Comparison of Simulated Urban and Rural Diesel Concentrations (  g/m 3 )

19. Elemental Carbon (1) (  g/m 3 ) Simulation vs. Measurements LocationSimulation (2) Measurements (3) Urban1 - 210.8 – 20 Suburban - Rural 0.2 – 2 Remote0.005 – 0.5 (1) Elemental carbon (EC) is an operational definition of the analytical measurement technique (2) assuming 50% EC in diesel particles (3) Seinfeld and Pandis, 1998 0.5 - 2 0.05 - 0.2

20. Elemental Carbon (1) (  g/m 3 ) Simulation vs. Measurements on July 15 LocationSimulation (2) Measurements (3) E. Forsythe, NJ0.531.16 Washington, D.C.1.511.89 (1) Elemental carbon (EC) is an operational definition of the analytical measurement technique (2) assuming 50% EC in diesel particles (3) IMPROVE

21. Conclusion CMAQ was modified to simulate two air toxics: –Benzene –Diesel particles Regional model gives realistic atmospheric concentrations for benzene and diesel particles Regional background can have a significant impact on peak urban concentrations Elemental carbon (EC) is not a good surrogate for diesel particles because of other EC sources