1. U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division October 21, 2009 Prakash Bhave, Ann Marie Carlton, Sergey Napelenok, Tad Kleindienst, John Offenberg, Michael Lewandowski, Mohammed Jaoui CMAS Conference Chapel Hill, NC October 19 – 21, 2009 Evaluation of CMAQ for Precursor-Specific Contributions to SOA in the Southeastern U.S.

2. U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division 1 Overview Background –Previous evaluations of CMAQ organic aerosol –Revised SOA treatment in CMAQ v4.7 Evaluation of current CMAQ results

3. U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division 2 CMAQ v4.5 Evaluation – OC & EC Summary of performance at all eastern U.S sites in 2001. Ref: K.W. Appel, et al. (2008), Atmos. Environ. 6057-6066. Across eastern U.S., CMAQ underpredicts OC & TC at most sites by ~1 μgC m -3 during summer factor of ~2 or more at many sites Median Bias (μgC m -3 )

4. U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division 3 Carbon Source Matrix

5. U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division 4 Modeled ÷ Observed Concentration Model Eval. – POA tracers (Jul’99) Bhave, Pouliot, & Zheng, Environ. Sci. Technol. (2007)

6. U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division 5 Radiocarbon Measurements ( 14 C) Technique takes advantage of fact that 14 C isotope is absent in fossil fuels PM 2.5 samples collected at Nashville on June 21 – July 13, 1999 were analyzed for 14 C C.W. Lewis et al., Atmos. Environ. (2004)

7. U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division 6 Model Eval. – Fossil-Fuel Carbon MSP sampler CMAQ 24h-avg Fireworks Excluding July 4 th influence, MB = -0.6  g/m 3 MB = Mean Bias

8. U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division 7 Model Eval. – Contemporary Carbon MSP sampler CMAQ 24h-avg Fireworks Excluding July 4 th influence, MB = -2.3  g/m 3 MB = Mean Bias

9. U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division 8 OC sec [  g/m 3 ] Legend: CMAQ results = solid line; empirical estimates = dashed line OC sec is underestimated in the Southeast during summer OC sec is overestimated in the west-coast states Model Evaluation – OC/EC Ratio Yu, Bhave, Dennis, & Mathur, Environ. Sci. Technol. (2007)

10. U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division 9 Missing Source(s) in CMAQ? (Summer OC in Southeast)

11. U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division 10 Tracer-Based Estimates of SOC Tracer-based method for estimating source contributions to ambient SOC Lab Experiments –Smog chamber irradiations of numerous VOC/NOx mixtures –Identified and quantified unique tracer compounds (e.g., methyl tetrols) using advanced GC/MS methods. –Computed tracer/SOC ratios for each SOA precursor (# tracers = 3 isop, 9 mono., 1 sesq., 1 arom.) Field Measurements –Collected 33 PM 2.5 samples in RTP throughout 2003 (2 – 5 day duration) –Quantified the same tracer compounds that were found in the chamber studies. –Estimated ambient SOC contribution from each VOC precursor, using the tracer/SOC ratios. See Kleindienst et al. (Atmos. Environ., 41: 8288-8300, 2007) for details. Greatest source of uncertainty: - Are the tracer/SOC ratios measured in the chamber equal to those in the atmosphere? Approach: -Accept the tracer estimates at face value until better information becomes available.

12. U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division 11 Tracer-Based EstimatesCMAQ v4.6 Results CMAQ v4.6 had… the wrong seasonal cycle for total SOC too much monoterpene SOC (especially in Spring & Fall) not enough aromatic SOC no isoprene or sesquiterpene SOC (also noted by Morris et al., 2006) Secondary Organic Carbon (μgC m -3 ) Kleindienst, Jaoui, Lewandowksi, Offenberg, Lewis, Bhave, & Edney, Atmos. Environ. (2007)

13. U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division 12 Organic PM 2.5 high-yield aromatics long alkanes ANTHROPOGENIC EMISSIONS low-yield aromatics ATOL1, ATOL2 AXYL1, AXYL2 SV_TOL1 SV_TOL2 ∙OH/NO SV_XYL1 SV_XYL2 ∙OH/NO monoterpene BIOGENIC EMISSIONS SV_TRP1 SV_TRP2 O 3 P, NO 3 ∙OH,O 3 ATRP1, ATRP2 Non-volatile EMISSIONS POA AALK SV_ALK ∙OH Pathways do not contribute to SOA SV_ISO1, SV_ISO2 SV_SQT O 3,O 3 P, or NO 3 ∙OH ∙OH,O 3, or NO 3 isoprene sesquiterpenes ASQT AISO1, AISO2 AISO3 H+H+ benzene ABNZ1, ABNZ2 SV_BNZ1 SV_BNZ2 ∙OH/NO AXYL3 ATOL3 ABNZ3 ∙OH/HO 2 AOLGB AOLGA AORGC ∙OH dissolution cloud water glyoxal methylglyoxal VOCs EMISSIONS CMAQ v4.7

14. U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division 13 CMAQ v4.6new SOA treatment Secondary Organic Carbon (μgC m -3 ) Did It Make a Difference? Model results from lowest layer are averaged by month 36km grid cell containing Research Triangle Park measurement site

15. U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division 14 CMAQ v4.6new SOA treatment Secondary Organic Carbon (μgC m -3 ) Did It Make a Difference? Model results from lowest layer are averaged by month 36km grid cell containing Research Triangle Park measurement site

16. U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division 15 Model Evaluation for 4 SOC Classes Tracer-Based EstimatesCMAQ – new SOA Model results are consistently low (29 out of 33 samples), especially during high-pollution episodes in Summer

17. U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division 16 Model Evaluation for 4 SOC Classes Tracer-Based Estimates [μgC m -3 ] CMAQ Model Results [μgC m -3 ]

18. U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division 17 Summary Despite significant updates, CMAQ results still fall short of observed SOC in Southeast during Summer Missing isoprene SOC –May be due to insufficient in- cloud formation Missing aromatic SOC –May require a VBS approach Monoterpene & sesquiterpene SOC are in the right ballpark Preliminary results from Midwest: –All 4 SOC types underestimated from May – Sept. –See poster by Napelenok et al. References Appel, K.W.; Bhave, P.V.; Gilliland, A.B.; Sarwar, G.; Roselle, S.J. Evaluation of the Community Multiscale Air Quality (CMAQ) Model Version 4.5: Sensitivities Impacting Model Performance; Part II – Particulate Matter, Atmospheric Environment, 2008, 42:6057-6066. Bhave, P.V.; Pouliot, G.A.; Zheng, M. Diagnostic Model Evaluation for Carbonaceous PM2.5 Using Organic Markers Measured in the Southeastern U.S., Environmental Science and Technology, 2007, 41:1577- 1583 Bhave, P. Yu, S.; Lewis, C. Evaluation of a Model for Predicting the Fossil-Fuel and Biogenic Contributions to Fine Particulate Carbon, American Association of Aerosol Research, 11B1, Austin, October 2005 Kleindienst, T.E.; Jaoui, M., Lewandowski, M.; Offenberg, J.H.; Lewis, C.W.; Bhave, P.V.; Edney, E.O. Estimates of the Contributions of Biogenic and Anthropogenic Hydrocarbons to Secondary Organic Aerosol at a Southeastern US Location, Atmospheric Environment, 2007, 41:8288-8300 Yu, S.; Bhave, P.V.; Dennis, R.L.; Mathur, R. Seasonal and Regional Variations of Primary and Secondary Organic Aerosols over the Continental United States: Semi- empirical estimates and model evaluation, Environmental Science and Technology, 2007, 41: 4690-4697

19. U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division 18 Extra Figures

20. U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division 19 Site Location – Aerial Photo RTP sampling site located at 35.894ºN and 78.877ºW

21. U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division 20 Site Location – Gridded Map w. Counties MM5 Land Use Categories Site is in NE corner of grid cell (121,50); ~4km from nearest neighboring cell. LEGEND Mixed Forest Cropland/Woodland Mosaic Evergreen Needleleaf Forest Dryland Cropland and Pasture Deciduous Broadleaf Forest