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

CMAQ

Chris Nolte

Atmospheric Modeling Division

National Exposure Research Laboratory

October 19, 2004

Acknowledgements

Prakash Bhave

Robin Dennis

K. Max Zhang

Tony Wexler

Lucille Bender

Charles Chang

Outline

• Characteristics of the CMAQ and CMAQ-AIM aerosol modules

• Approach

• Results

• Conclusions & Future Work

Comparison between CMAQ and CMAQ-AIM

Feature CMAQ CMAQ-AIM

Size representationModal

(3 lognormal modes)

Sectional

(currently 9 sections)

Mass transfer to

fine PMInstantaneous

equilibriumDynamic

Mass transfer to coarse PM

None Dynamic

Thermodynamics ISORROPIA AIM

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

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

Results: O3Average ozone concentrations are identical in the two models.

Results: O3Average ozone concentrations are identical in the two models.

Excellent agreement in average SO4 concentrations Results: SO4

Excellent agreement in average SO4 concentrations Results: SO4

O3 and SO4 Difference Plots(CMAQ-AIM minus CMAQ)

O3 and SO4 Difference Plots(CMAQ-AIM minus CMAQ)

Results: Total NO3

Results: Total NO3

TNO3 Difference Plots (CMAQ-AIM minus CMAQ)

Results: Fine NO3

Results: Fine NO3

Fine NO3 Difference Plots (CMAQ-AIM minus CMAQ)

Results: HNO3

Results: HNO3

HNO3 Difference Plots(CMAQ-AIM minus CMAQ)

Results: NH4

Results: NH4

NH4 Difference Plots(CMAQ-AIM minus CMAQ)

Conclusions• Initial comparisons of CMAQ and CMAQ-AIM show

good agreement.

• Differences in nitrate partitioning may be due to:(1) Equilibrium assumption vs. dynamic mass transfer(2) Different thermodynamics - activity coefficients

(3) 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 Commerce’s 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.