Using CMAQ-AIM to Evaluate the Gas-Particle Partitioning Treatment in CMAQ

1
Using CMAQ-AIM to Evaluate the Gas-Particle
Partitioning Treatment in CMAQ

• Chris Nolte
• Atmospheric Modeling Division
• National Exposure Research Laboratory
• October 19, 2004

2
Acknowledgements

• Prakash Bhave
• Robin Dennis
• K. Max Zhang
• Tony Wexler
• Lucille Bender
• Charles Chang

3
Outline

• Characteristics of the CMAQ and CMAQ-AIM aerosol
  modules
• Approach
• Results
• Conclusions Future Work

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Comparison between CMAQ and CMAQ-AIM
Feature CMAQ CMAQ-AIM
Size representation Modal (3 lognormal modes) Sectional (currently 9 sections)
Mass transfer to fine PM Instantaneous equilibrium Dynamic
Mass transfer to coarse PM None Dynamic
Thermodynamics ISORROPIA AIM
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Comparison between CMAQ and CMAQ-AIM (continued)
Feature CMAQ CMAQ-AIM
Equilibrium State Metastable Stable
Sea salt No Yes
N2O5 ? HNO3 heterogeneous conversion No No
Coagulation Yes No
6
Approach

• Model to model comparison
• Continental US domain, 32 km grid cell size, 24
  vertical layers, SAPRC 99 chemical mechanism
• Summer (Jun 24 Jul 31, 2001) and winter (Dec 24
  Jan 31, 2002) modeling periods

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Results O3
Average ozone concentrations are identical in the
two models.
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Results O3
Average ozone concentrations are identical in the
two models.
9
Excellent agreement in average SO4 concentrations
Results SO4
10
Excellent agreement in average SO4 concentrations
Results SO4
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O3 and SO4 Difference Plots(CMAQ-AIM minus CMAQ)
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O3 and SO4 Difference Plots(CMAQ-AIM minus CMAQ)
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Results Total NO3
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Results Total NO3
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TNO3 Difference Plots (CMAQ-AIM minus CMAQ)
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Results Fine NO3
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Results Fine NO3
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Fine NO3 Difference Plots (CMAQ-AIM minus CMAQ)
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Results HNO3
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Results HNO3
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HNO3 Difference Plots(CMAQ-AIM minus CMAQ)
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Results NH4
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Results NH4
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NH4 Difference Plots(CMAQ-AIM minus CMAQ)
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Conclusions

• Initial comparisons of CMAQ and CMAQ-AIM show
  good agreement.
• Differences in nitrate partitioning may be due
  to
• Equilibrium assumption vs. dynamic mass transfer
• Different thermodynamics - activity coefficients
• Coarse mode sink for NO3
• Future work will involve trying to evaluate these
  differences independently
• (1) Run CMAQ-AIM without sea-salt emissions
• (2) Run CMAQ-AIM with ISORROPIA

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 Commerces National Oceanic
and Atmospheric Administration (NOAA) and under
agreement number DW13921549. Although it has
been reviewed by EPA and NOAA and approved for
publication, it does not necessarily reflect
their policies or views.