1. Implementation of the Particle & Precursor Tagging Methodology (PPTM) for the CMAQ Modeling System: Mercury Tagging 5 th Annual CMAS Conference Research Triangle Park, NC 17 October 2006 Tom Braverman, EPA OAQPS Tom Myers, ICF International Dwight Atkinson, EPA OW EPA

2. Presentation Outline Background & objectives Overview of PPTM Implementation of PPTM for mercury in the CMAQ model Testing & example results Summary

3. Background & Objectives for Mercury Tagging Atmospheric deposition of mercury is a source of mercury contamination in surface waters As of 2005, more than 6,000 bodies of water were identified as mercury impaired and more than 2,000 were issued mercury fish advisories Key objective of mercury tagging is to quantify the contribution from selected sources/source categories to mercury deposition for bodies of water, hydrologic zones, and watershed regions

4. Overview of PPTM: Concepts Emissions (or initial/boundary condition) species are tagged in the emissions (or IC/BC) files and continuously tracked throughout the simulation Tags can be applied to source regions, source categories, individual sources, initial conditions, and/or boundary conditions PPTM quantifies the contribution of tagged sources to simulated species concentrations & deposition

5. Overview of PPTM: Concepts Within the model, tagging is accomplished by the addition of duplicate species (e.g., HG_t1, HG_t2) Tagged species have the same properties and are subjected to the same processes (e.g., advection, chemical transformation, deposition) as the actual species Base simulation results not affected by tagging

6. Overview of PPTM: Attributes and Limitations Attributes: Straightforward and true to modeled results (limited normalization or partitioning assumptions) Technique has been extensively tested and refined in REMSAD (over a period of 7 years) before being incorporated into CMAQ Limitations: Currently number of tags is limited by # of output species allowed by CMAQ (hard-coded in libraries) Mercury tagging applied separately (currently) CMAQ run times and file sizes are increased

7. Overview of PPTM: Attributes and Limitations Other Notes: Provides information about contribution, and not response to changes in emissions Difference between sum of all tags and overall concentration gives an estimate of the uncertainty effects in the contribution estimates Tags are additional species in the model, which allows postprocessing of the outputs using standard methods (applicable for any species)

8. Implementation of PPTM for CMAQ: Mercury CMAQ version 4.5.1 Tagged elements include: HG, HGIIGAS, HGIIAER, APHGI, APHGJ Key considerations/assumptions: Linear processes simulated directly (e.g., advection, dry deposition) Potentially non-linear processes (e.g., gas-phase chemistry, aqueous chemistry, particle dynamics) calculated for total species and apportioned to tags Simulation always includes the overall species tag and may include up to 7 additional tags; individual tags do not have to add up to the overall tag

9. Implementation of PPTM for CMAQ: Mercury CPU requirements increased by approximately 30 percent for 3 tags Documentation/user’s guide available from EPA or ICF as follows: Douglas, S., T. Myers and Y. Wei. 2006. “ Implementation of Mercury Tagging in the Community Multiscale Air Quality (CMAQ) Model.” Prepared for EPA, OAQPS, Research Triangle Park, NC. ICF International, San Rafael, California (06-051).

10. Testing of PPTM for Mercury: Model Inputs 2001 Penn State mesoscale meteorological model version 5 (MM5) 1999 NEI mercury emissions inventory, except 2002 NEI for MWI 2001 criteria pollutant emissions 36 km horizontal grid square resolution 14 vertical layers (surface layer – 38 meters) Harvard’s GEOS-CHEM global model used for inflow of pollutants to the modeling domain (varied horizontally and vertically every three hour period)

11. Testing of PPTM for Mercury Limited period test runs used to confirm Base simulation results are the same w/ & w/o tagging Location and footprint of tags is reasonable (consistent with tag specifications & met conditions) Various types of tags (geographic, source category & combinations, per requested examples) work correctly One-month test runs (July 2001) w/o tagging source-category tags (T1=EGU, T2=other, T3=IC/BC)

12. Example CMAQ PPTM Mercury Tagging Results: Elemental Hg Tag 1: EGU Tag 2: Other CMAQ Base Tag 3: IC/BC

13. Example CMAQ PPTM Mercury Tagging Results: Divalent Hg Tag 1: EGU Tag 2: Other CMAQ Base Tag 3: IC/BC

14. Example CMAQ PPTM Mercury Tagging Results: Particulate Hg Tag 1: EGU Tag 2: Other CMAQ Base Tag 3: IC/BC

15. Example CMAQ PPTM Mercury Tagging Results: Dry Deposition Tag 1: EGU Tag 2: Other CMAQ Base Tag 3: IC/BC

16. Example CMAQ PPTM Mercury Tagging Results: Dry Deposition IN26 MD13 PA13 FL34 Difference/ uncertainty

17. Example CMAQ PPTM Mercury Tagging Results: Dry Deposition IN26 FL34 PA13 MD13 Results vary considerably by site

18. Summary Mercury tagging has been implemented in version 4.5.1 of CMAQ Mercury tagging can be used to track the fate of mercury emissions from selected sources and to quantify the contribution of the emissions to CMAQ- derived concentration and deposition estimates Initial test results indicate that numerical effects (uncertainties) are small, compared to contribution estimates Plan to perform further mercury tagging work for other months and at 12 km grid square resolution