1. Using CMAQ-AIM to Evaluate the Gas-Particle Partitioning Treatment in CMAQ Chris Nolte Atmospheric Modeling Division National Exposure Research Laboratory October 19, 2004

2. Acknowledgements Prakash Bhave Robin Dennis K. Max Zhang Tony Wexler Lucille Bender Charles Chang

3. Outline Characteristics of the CMAQ and CMAQ-AIM aerosol modules Approach Results Conclusions & Future Work

4. Comparison between CMAQ and CMAQ-AIM FeatureCMAQCMAQ-AIM Size representation Modal (3 lognormal modes) Sectional (currently 9 sections) Mass transfer to fine PM Instantaneous equilibrium Dynamic Mass transfer to coarse PM NoneDynamic ThermodynamicsISORROPIAAIM

5. Comparison between CMAQ and CMAQ-AIM (continued) FeatureCMAQCMAQ-AIM Equilibrium StateMetastableStable Sea saltNoYes N 2 O 5 → HNO 3 heterogeneous conversion No CoagulationYesNo

6. Approach Model to model comparison Continental US domain, 32 km grid cell size, 24 vertical layers, SAPRC 99 chemical mechanism Summer (Jun 24 – Jul 31, 2001) and winter (Dec 24 – Jan 31, 2002) modeling periods

7. Results: O3 Average ozone concentrations are identical in the two models.

8. Results: O3 Average ozone concentrations are identical in the two models.

9. Excellent agreement in average SO 4 concentrations Results: SO4

10. Excellent agreement in average SO 4 concentrations Results: SO4

11. O 3 and SO 4 Difference Plots (CMAQ-AIM minus CMAQ)

13. Results: Total NO 3

15. TNO 3 Difference Plots (CMAQ-AIM minus CMAQ)

16. Results: Fine NO 3

18. Fine NO 3 Difference Plots (CMAQ-AIM minus CMAQ)

19. Results: HNO 3

21. HNO 3 Difference Plots (CMAQ-AIM minus CMAQ)

22. Results: NH 4

24. NH 4 Difference Plots (CMAQ-AIM minus CMAQ)

25. Conclusions Initial comparisons of CMAQ and CMAQ-AIM show good agreement. Differences in nitrate partitioning may be due to: (1) Equilibrium assumption vs. dynamic mass transfer (2) Different thermodynamics - activity coefficients (3) Coarse mode sink for NO 3 Future work will involve trying to evaluate these differences independently (1) Run CMAQ-AIM without sea-salt emissions (2) Run CMAQ-AIM with ISORROPIA The research presented here was performed under the Memorandum of Understanding between the U.S. Environmental Protection Agency (EPA) and the U.S. Department of Commerce’s National Oceanic and Atmospheric Administration (NOAA) and under agreement number DW13921549. Although it has been reviewed by EPA and NOAA and approved for publication, it does not necessarily reflect their policies or views.