5 th Annual CMAS Conference Research Triangle Park, NC 17 October 2006 Tom Braverman, EPA OAQPS

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

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 CMAQ Base Tag 2: Other Tag 3: IC/BC

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

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

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

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

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

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