1. GMI Box Model Intercomparison Update D. B. Considine, J. R. Olson, P. S. Connell GMI Science Team Meeting Fall, 2003

2. History GMI needs a strat/trop combined chemical mechanism/ solver to create a combined version of GMI. NASA LaRC has such a mechanism which is currently incorporated into two global models. Science team decided 11/2002 that box model intercomparison with other combined mechanisms/ GMI-trop/GMI-strat was appropriate 1st step. What are the differences between LaRC mechanism and others Are differences reasonable and understandable?

3. Summary of Recent Activities Ported “GMI Box Model” to LaRC Fixed a few coding errors in model Completed initial comparison of GMI trop chem mechanism with LaRC combined solver Implemented “Carter 4-product” isoprene scheme in LaRC solver Completed box model testing of isoprene scheme, currently doing global model testing.

4. Box Model Intercomparison Description 9 scenarios: 5 “baseline,” 4 “non-methane hydrocarbon” Standardized photolysis coefficients from Kawa lookup Some standardized reaction rates - JPL 00 Scenarios run for 10 days, no emissions, start at 00 Z GMI box model with trop chem scheme Same reactions as global model Solver is “DLSODE,” Hindmarsh’s stiff ODE scheme instead of SMVGEAR (both GEAR solvers) LaRC box model with LaRC combined scheme Not a Gear solver - PCE assumptions, families, etc. 1/2 hr time step 55 transported species, 86 calculated 220 thermal rxns, 50 photolysis rxns NMHC scheme different from Harvard approach

5. Scenario Descriptions RunMonthAltitudeInit O3Init NOxInit HC BL 1JulySurfaceMediumHighNo BL 2NovSurfaceLowHighNo BL 3NovSurfaceMediumHighNo BL 4JulySurfaceMediumLowNo BL 5Nov236 hPaHighLowNo HC 1NovSurfaceMediumHigh HC 2JulySurfaceMediumHigh HC 3Nov365.5 hPaMediumHigh HC 4Mar694.7 hPaMediumLow Temperature = 15 o C except in lofted cases

6. LaRC Run Versions Peroxide oxidation branching matched to GMI Organic nitrate production matched to GMI RO2 + NO branching matched to GMI Standard Revised 1: Remove NO3 + peroxy radical rxns Revised 2: Revised 1 +... I have the specific changes if you want to see them...

7. Nov Med O3 High NOx Nov Low O3 High NOx July, Med O3, High NOx July Med O3 Low NOx Nov, 236 mbar High O3 Low NOx Nov, Med O3,High NOx July Med O3 High NOx 365.5 mbar Nov Med O3 High NOx March Med O3 Low NOx Low NMHC 694.7 mbar

8. LaRC is within ~10% of GMI in all cases after 10 days. BL2 case (low O3, low sun), shows sunrise/set discrepancies. BL 5 case (low NOx, low sun, mid troposphere) shows very close agreement. HC 3 case (urban lofted, low sun) disagrees in trend. LaRC more frequently underestimates O3 relative to GMI.

10. LaRC NO2 diurnal cycle typically agrees well with GMI. Revision 1 improves nighttime agreement substantially. HC3, HC4 cases do not agree well.

11. NO3 nightime agreement improved by revision 1 in baseline 1, 3, and hydrocarbon 2. Agreement worsened in hydrocarbon 1,3, 4.

12. OH generally agrees well between LaRC and GMI mechanisms. In HC 1 and HC 3 cases LaRC OH is higher (Note - in these cases HO2 is lower).

13. CH3OOH agreement is sometimes good, and sometimes substantially underpredicted by LaRC compared to GMI (HC1, HC3). This is likely due to higher OH/HO2 ratio.

17. Summary and Conclusions LaRC O3 time series in good agreement with GMI-Trop: Differences ~ ±10% after 10 day simulation Largest discrepancies in urban lofted case substantially improved by kinetic revisions Suggests differences are understandable and not related to formulation (species choices, etc). High sensitivity to basic assumptions about NMHC reactions Additional scenarios to test isoprene mechanism, addition of emissions could be undertaken. LaRC combined chemical scheme is a viable candidate for inclusion in GMI Global. Intercomparison of (tropospheric) solvers in global model following box model intercomp publishible?