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Enhancing Aerosol Size Distribution Modeling for Improved Air Quality Assessments

Explore the impact of changes to particle emissions and nucleation on aerosol size distribution performance. Discuss the significance of size distribution modeling in assessing health effects, with a focus on ultrafine PM2.5 drivers. Analyze the CMAQ simulation results and observational datasets from PNW 2001, highlighting the challenges in emission size distribution modeling and the importance of accounting for nucleation processes. Evaluate the implications of different nucleation models and methods for improving emissions size distributions at a 4 km scale. Understand the sensitivity of emissions on aerosol size parameters and learn how to enhance modeling accuracy for better air quality assessments.

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Enhancing Aerosol Size Distribution Modeling for Improved Air Quality Assessments

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  1. Aerosol Size Distribution Performance Based on Changes to Particle Emissions and Nucleation Robert A. Elleman & David S. Covert Department of Atmospheric Sciences University of Washington

  2. Importance of Size Distribution Modeling • Health Effects in Ultrafine Size Distribution PM2.5 Drivers.com www.eere.energy.gov

  3. CMAQ Simulation • CMAQ v4.4 (September 2004) • 4 km horizontal resolution • 22 levels -- lowest layer is ~30 meters • 4 day spin-up • 3 day simulation • 00 UTC 08/26 – 00 UTC 08/29, 2001 Observational Datasets PNW 2001 Pacific 2001

  4. CMAQ v4.4 Number Concentrations Flight track Pacific Standard Time = UTC - 8

  5. Ternary Number Concentrations Flight track Pacific Standard Time = UTC - 8

  6. Emission Size Distribution • Can cause consistent number underprediction • Outdated science in model biases fewer, larger particles • Nucleation mode • Not all nucleated particles survive to be observed and included in Aitken mode

  7. “Condensation Sink” = H2SO4 Growth Rate Process Nano-mode Kerminen, V.-M., and M. Kulmala, 2002: Analytical formulae connecting the “real” and the “apparent” nucleation rate and the nuclei number concentration for atmospheric nucleation events. J. Aerosol Sci., 33, 609-622. • Few 1 nm particles survive to Aitken mode

  8. Nucleation Model # Concentrations Ternary Ternary w/Proc obs Binary/None Ternary Ternary w/Proc Binary/None

  9. Nucleation Model Size Distributions • Ternary nucleation with processing to 10 nm best simulates the shape of the size distribution and the Aitken mode diameter

  10. Emission Size Distribution • Can cause consistent number underprediction • Outdated science in model biases fewer, larger particles • Nucleation mode • Not all nucleated particles survive to be observed and included in Aitken mode

  11. 4 km Improve Emissions Size Distributions • Scale to 4 km grid • All processes < 4 km scale must be parameterized • Use “urban background” measurements to constrain model • Mostly from traffic Emissions Sensitivity Matrix

  12. Effect of Emission Size Distribution Number Enhancement Size Parameters

  13. Ternary Ternary w/Processing Emission Size Distribution CMAQ v4.4 Conclusion

  14. Contact Information: Robert Elleman rob@atmos.washington.edu University of Washington (206) 543-9144 Department of Atmospheric Sciences Seattle, WA, USA

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