GMI Box Model Intercomparison Update

D. B. Considine, J. R. Olson, P. S. ConnellGMI Science Team Meeting

Fall, 2003

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?

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.

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

Scenario Descriptions

Run Month Altitude Init O3 Init NOx Init HC

BL 1 July Surface Medium High No

BL 2 Nov Surface Low High No

BL 3 Nov Surface Medium High No

BL 4 July Surface Medium Low No

BL 5 Nov 236 hPa High Low No

HC 1 Nov Surface Medium High High

HC 2 July Surface Medium High High

HC 3 Nov 365.5 hPa Medium High High

HC 4 Mar 694.7 hPa Medium Low Low

Temperature = 15oC except in lofted cases

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 wantto see them ...

NovMed O3High NOx

NovLow O3High NOx

July, Med O3, High NOx

JulyMed O3Low NOx Nov, 236 mbar

High O3Low NOx

Nov, Med O3,High NOx

July Med O3High NOx

365.5 mbarNov Med O3High NOx

MarchMed O3Low NOxLow NMHC

694.7 mbar

• 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.

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

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

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

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

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?