Development of a Multipollutant Version of the Community Multiscale Air Quality (CMAQ) Modeling System Shawn Roselle, Deborah Luecken, William Hutzell, Russell Bullock, Golam Sarwar, and Kenneth Schere U.S. EPA/ORD/NERL; NOAA/OAR/ARL Atmospheric Modeling Division Research Triangle Park, NC

Background Humans and ecosystems can be exposed to multiple pollutants at the same time Chemistry, transport and fate of pollutants are interrelated CMAQ was developed to provide a “one-atmosphere” approach for air quality modeling State-of-science capabilities for modeling multiple air quality issues, including tropospheric ozone, fine particles, hazardous air pollutants (HAPs), acid deposition, and visibility degradation

Background (continued) CMAQ utilized by EPA/OAR/OAQPS to evaluate benefits and effectiveness of various control programs: Clean Air Interstate Rule (CAIR) Clean Air Mercury Rule (CAMR) Clean Air Visibility Rule (CAVR) Increasing interest for modeling multipollutants, including criteria and hazardous air pollutants, in a single modeling framework for air quality management Predict ozone, PM, mercury, and other HAPs concentrations and interactions all within the same model simulation Ability to examine co-benefits of emission reductions

Current Capabilities (CMAQv4.6) Several configurations available for CMAQ Base model1 Carbon Bond ’05 (CB05) and SAPRC99 Aerosol module version 4 (aero4 or AE4) Cloud chemistry HAPs1 Includes gas-phase HAPs, toxics metals, and diesel PM CB05-HAPs chemical mechanism includes chlorine chemistry SAPRC99 version is also available Mercury1 CB05-Mercury mechanism includes chlorine chemistry Additional gas-phase species Elemental mercury and reactive gaseous mercury Aerosol species Particulate Hg (Aitken and Accumulation mode) Additional gas-phase reactions Major modifications to aqueous phase chemistry 1Although versions exist for CB4 and aero3 (AE3), these will no longer be supported beginning with the 2008 CMAQ release

Approach Merge capabilities from HAPs and mercury model versions Differences in model results were related to chlorine emissions and chemistry Normalize results across the different model configurations

Number of Species for Different Model Configurations Gas-phase Aerosol Non-reactive Total Species (total transported) Base CB05 cb05_ae4_aq 56 34 12 102 (79) CB05 w/ Chlorine cb05cl_ae4_aq 62 11 107 (82) CB05 Mercury cb05hg_ae4_aq 65 36 112 (88) CB05 HAPs cb05cltx_ae4_aq 73 58 33 164 (141) CB05 Multipollutant cb05txhg_ae4_aq 76 60 169 (147)

Multipollutant Model Tests Model platform Simulation period: July 22-31, 2001 Domain: continental U.S.; 36 km grid resolution; 14 layers Meteorological Data MM5 Simulations (36 km grid resolution; 34 layers) Emissions Merged existing emissions files for criteria air pollutants (CAPs), HAPs and mercury (1999 NEI; added mercury emissions) Simulations: Multipollutant, HAPs, mercury, CB05 w/ chlorine chemistry, and base-CB05 Other model sensitivity tests

Max diff over all hours: Multipollutant vs. HAPs Ozone (10-day Maximum) HAPs Model Multipollutant Model Mercury Model Max diff over all hours: Multipollutant vs. HAPs Differences caused by Cl2 emissions being zeroed-out in HAPs Model to keep O3 same as base CB05

Chlorine (10-day Average) HAPs Model Multipollutant Model Mercury Model Note scale difference CB05 w/ Chlorine Chem. Model Cl2 emissions were not included in HAPs Model

Hydrochloric Acid (10-day Average) HAPs Model Multipollutant Model Mercury Model CB05 w/ Chlorine Chem. Model Cl2 emissions not included in HAPs model HAPs model includes reaction: <CL21> HCL + OH = CL # 6.58E-13^1.16 @ -58 Minimum value set for Cl- in mercury version of AQCHEM Cl- (aq)  HCl and ACLJ

Hydrochloric Acid (10-day Average) HAPs Model w/ Cl2 emis Multipollutant w/ AQCHEM mod Mercury Model CB05 w/ Chlorine Chem. Model Multipollutant w/ AQCHEM mod & with HCl emissions Cl2 emissions now included in HAPs model Minimum value for Cl- reduced by several orders of magnitude in multi-pollutant version of AQCHEM None of the models include HCl emissions

Summary of the Normalization Process Turned on Cl2 emissions in HAPs model Turned on HCl emissions in all models with chlorine chemistry: HAPs, Mercury, CB05 with chlorine chemistry, and Multipollutant Reduced background aqueous Cl- concentration in aqueous chemistry to improve mass balance (in multipollutant and mercury models) Added HCl+OH gas phase reaction to mercury model and CB05 w/ chlorine chemistry model

Ozone: 10-day Maximum HAPs Model Multipollutant Model Mercury Model All Hours (ppb) MAX DIFF MIN DIFF 0.456 -0.081 All Hours (ppb) MAX DIFF MIN DIFF 0.063 -0.037

CB05 w/ Chlorine Chem. Model Ozone: 10-day Maximum CB05 w/ Chlorine Chem. Model Multipollutant Model Base CB05 Model All Hours (ppb) MAX DIFF MIN DIFF 0.471 -0.073 All Hours (ppb) MAX DIFF MIN DIFF 36.55 -0.995

Sulfate (10-day Average) HAPs Model Multipollutant Model Mercury Model (ug/m3) MAX DIFF MIN DIFF 0.032 -0.026 (ug/m3) MAX DIFF MIN DIFF 0.001 -0.001

Sulfate (10-day Average) CB05 w/ Chlorine Chem. Model Multipollutant Model Base CB05 Model (ug/m3) MAX DIFF MIN DIFF 0.030 -0.028 (ug/m3) MAX DIFF MIN DIFF 0.023 -0.051

Average Elapsed CPU Time (minutes) per Simulation Day* Model Chemical Solver ros3 ebi Base CB05 19.9 16.6 CB05 w/ chlorine chemistry 22.2 18.9 CB05 mercury 23.8 20.7 CB05 HAPs 33.7 30.7 CB05 Multipollutant 35.9 32.0 *SGI-Altix 4700, 8 PEs

Summary A multipollutant version of CMAQ has been developed and tested An internal version of the model is being applied and evaluated by OAQPS Sharon Phillips will present results from multipollutant model applications in Session 8 Multipollutant model will be included in next release

2008 CMAQ Release Based on current model test results, plan to use a version of CB05 w/chlorine chemistry as the base configuration for the next model release Consistent results for the different model configurations Requires emissions for Cl2 and HCl Next release Fall 2008

Disclaimer: 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 DW13921548. This work constitutes a contribution to the NOAA Air Quality Program. It has not been reviewed by EPA or NOAA and has not been approved for publication, and does not necessarily reflect their views or policies.