1. 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

2. 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

3. 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

4. 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

5. 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

6. 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)

7. 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

8. 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

9. 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

10. 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 # -58
Minimum value set for Cl- in mercury version of AQCHEM
Cl- (aq)  HCl and ACLJ

11. 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

12. 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

13. Ozone: 10-day Maximum HAPs Model Multipollutant Model Mercury Model
All Hours (ppb)
MAX DIFF MIN DIFF
All Hours (ppb)
MAX DIFF MIN DIFF

14. 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
All Hours (ppb)
MAX DIFF MIN DIFF

15. Sulfate (10-day Average)
HAPs Model
Multipollutant Model
Mercury Model
(ug/m3)
MAX DIFF MIN DIFF
(ug/m3)
MAX DIFF MIN DIFF

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

17. 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

18. 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

19. 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

20. 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 DW 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.