1. Plume-in-Grid Modeling for PM & Mercury Prakash Karamchandani, Krish Vijayaraghavan, Shu-Yun Chen & Christian Seigneur AER San Ramon, CA 5th Annual CMAS Conference October 16–18, 2006 Chapel Hill, NC

2. Why Use Plume-in-Grid Approach? Plume Size vs Grid Size (from Godowitch, 2004) Artificial dilution of stack emissions Unrealistic near-stack plume concentrations Incorrect representation of plume chemistry Incorrect representation of plume transport Limitations of Purely Grid-Based Approach

3. Plume Chemistry & Relevance to PM and Mercury Modeling Early Plume Dispersion NO/NO 2 /O 3 chemistry 1 2 Mid-range Plume Dispersion Reduced VOC/NO x /O 3 chemistry — acid formation from OH and NO 3 /N 2 O 5 chemistry Long-range Plume Dispersion 3 Full VOC/NO x /O 3 chemistry — acid and O 3 formation Possible reduction of Hg II to Hg 0

4. Mercury Chemistry in Power Plant Plumes Evidence of Hg II reduction in power plant plumes (Edgerton et al., ES&T, 2006; Lohman et al., ES&T, 2006) Reduction of Hg II by SO 2 (possibly via heterogeneous reaction on particles) is compatible with the global Hg cycling budget (Seigneur et al., J. Geophys. Res., in press)

5. CMAQ-MADRID-APT-Hg Based on CMAQ v 4.5.1, March 2006 release MADRID: Model of Aerosol Dynamics, Reaction, Ionization and Dissolution APT: Advanced Plume Treatment with embedded plume model SCICHEM (state-of-the science treatment of stack plumes at the sub-grid scale) Mercury treatment included Consistent treatments for chemical transformations (gas- and aqueous-phase) and PM in the host model and the embedded plume model

6. Model Components CMAQ v. 4.5.1 MADRID PM Treatment with Mercury CMAQ-MADRID-Hg SCICHEM-MADRID-Hg PM and Hg Treatment based on CMAQ-MADRID-Hg CMAQ-MADRID-APT-Hg

7. SCICHEM Three-dimensional puff-based model Second-order closure approach for plume dispersion Puff splitting and merging Treatment of plume overlaps Optional treatment of building downwash Optional treatment of turbulent chemistry PM, gas-phase and aqueous-phase chemistry treatments consistent with host model

8. Atmospheric Mercury Mercury is present mostly as three “species” in the atmosphere –Elemental mercury (Hg 0 ) –Divalent gaseous mercury: HgCl 2, Hg(OH) 2, HgO, etc. referred to collectively as Hg II or reactive gaseous mercury (RGM) –Particulate-bound mercury: Hg II or Hg 0 adsorbed on PM mostly divalent referred to collectively as Hg p

9. Atmospheric Chemistry of Mercury

10. Application to Southeastern U.S. Simulation period: 2002 Grid resolution: 12 km x 12 km, 19 layers (up to ~15 km) Meteorology and emissions inventory from Georgia EPD and VISTAS Non-Hg ICs/BCs from Georgia EPD –5 day model spinup for each quarter Two annual simulations with CMAQ-MADRID-APT-Hg –With SO 2 + Hg II reduction reaction –Without this reaction

11. Modeling Domain and Locations of APT sources

12. Boundary Conditions for Mercury Species Boundary conditions (BCs) for mercury were obtained from a 2001 simulation conducted over the United States with the Trace Element Analysis Model (TEAM) Spatially and temporally (hourly) varying BCs of Hg 0, Hg II, and Hg p

13. Preliminary Results from Plume Event Evaluations Several power plant plume events observed at SEARCH monitoring locations (Edgerton et al., ES&T, 2006) To compare the modeled plume events with observations, the plume information in the embedded plume model is used to calculate subgrid-scale concentrations downwind of the power plant impacting a SEARCH monitoring location Plume concentrations are sampled at an array of receptors along an arc; the center of the arc is the power plant of interest and the arc extends to 30 o on each side of the monitoring location The receptor location with the closest match of modeled SO 2 peak increment to the observed peak increment is used for comparison purposes

14. Placement of Receptors for Plume Event Evaluations

15. Monitoring Stations in SEARCH network http://www.atmospheric-research.com/studies/SEARCH/index.html operated by Atmospheric Research & Analysis, Inc. (ARA)

16. Comparison of Measured and Simulated Peak SO 2 Increments Date Monitoring Location Measured Peak (ppb) Simulated Peak (ppb) MADRIDMADRID-APT July 5YRK491942 July 18PNS121121 July 19PNS944 July 20BHM111611 July 21YRK671221 July 21BHM131< 1 July 27CTR34313 July 30BHM191119 July 31BHM101513 July 31YRK858

17. Comparison of Measured and Simulated Peak SO 2 Increments Date Monitoring Location Measured Peak (ppb) Simulated Peak (ppb) MADRIDMADRID-APT Jan 3YRK18810 Jan 4YRK944 Jan 7YRK737 Jan 9YRK11813 Jan 10YRK1654 Jan 11CTR115 Jan 15YRK877

18. Plume Event on July 5, 2002 Hg Plume Increments Model Hg 0 (pg m -3 )Hg II (pg m -3 )Hg II /(Hg 0 + Hg II ) Obs.ModelObs.ModelObs.Model MADRID-APT-Hg with Hg II reduction reaction 4111904690.10.05 MADRID-APT-Hg without Hg II reduction reaction 41160461190.10.67 MADRID-Hg with Hg II reduction reaction 4112046230.10.54 MADRID-Hg without Hg II reduction reaction 4112046270.10.58 Source: Plant Bowen; Monitoring Location: Yorkville

19. Plume Event on July 21, 2002 Hg Plume Increments Model Hg 0 (pg m -3 )Hg II (pg m -3 )Hg II /(Hg 0 + Hg II ) Obs.ModelObs.ModelObs.Model MADRID-APT-Hg with Hg II reduction reaction 1887079420.290.37 MADRID-APT-Hg without Hg II reduction reaction 1886079960.290.62 Source: Plant Bowen; Monitoring Location: Yorkville

20. Power-Plant Contributions to 24 hr Average Sulfate Concentrations on July 5 CMAQ-MADRID-HgCMAQ-MADRID-APT-Hg

21. Power-Plant Contributions to 24 hr Hg Total Deposition on July 5 CMAQ-MADRID-HgCMAQ-MADRID-APT-Hg

22. Conclusions Observed plume events are better captured in the plume-in-grid approach than in the purely gridded approach Preliminary evaluation results suggest that observed RGM to TGM ratios during plume events are well simulated only when a plume-in-grid approach is used and a pathway for reducing Hg II to Hg 0 by SO 2 is included A purely gridded approach typically overestimates power plant contributions to PM 2.5 because SO 2 to sulfate and NO x to nitrate conversion rates are overestimated (Karamchandani et al., Atmos. Environ., in press) A purely gridded approach will also overestimate power plant contributions to RGM concentrations and depositions if a mechanism exists to reduce Hg II to Hg 0 in power plant plumes

23. Ongoing Work Complete simulations for entire calendar year Complete model performance evaluation: –SEARCH: Continuous gas, PM mass and components, Hg –Other air quality networks: AQS, IMPROVE, CASTNET –Wet deposition: NADP, MDN Control scenario simulations

24. Acknowledgements Funding: –EPRI (Eladio Knipping, Leonard Levin) –Southern Company (John Jansen) Input Files: –Georgia Environmental Protection Division (James Boylan, Maudood Khan) –VISTAS (Pat Brewer) SEARCH Plume Measurements: –Atmospheric Research & Analysis, Inc. (Eric Edgerton)