1. Testing the CBMhybrid chemical mechanism in TM5 Jason Williams Chemistry & Climate Division, KNMI The Netherlands Contributions from : A. Strunk ; R Scheele

2. 2 Motivation Positive Negative Modified CBM4 performs well but is out of date with respect to CBM development. Offline modeling diminishes in importance -> move towards CCM as standard Missing emission sources not included e.g. HCOOH and CH3OH. Long-lived organics under-represented. Too expensive currently for EC-earth application. Other CTMs typically include explicit hydrocarbons. More measurements becoming available. Additional tracers which are needed will slow code when used with online photolysis and M7 Continually tuning the model with emissions will never lead to good improvements in e.g. UTLS Manpower issues and funding for troubleshooting and development.

3. 3 CBM development (CB06) Yarwood et al, 9 th annual CMAS conf., 2010

4. 4 TM5 chemistry versions Benchmark (modified CBM4) Huijnen et al, GMD 2010 Online photolysis (modified CBM4) Williams et al, GMDD, 2011 Online photolysis (CBMhybrid Scheme) Modified CBM4 29 transported tracers 68 reaction rates 18 photolysis rates CBMhybrid 39 transported tracers (+35%) 101 reaction rates (+49%) 21 photolysis rates (+17%)

5. 5 Acetone in the CBM scheme OH + CH 3 C(O)CH 3 (+ O 2 )  CH 3 C(O)CH 2 O 2 HO 2 + CH 3 C(O)CH 2 O 2  ROOH CH 3 O 2 + CH 3 C(O)CH 2 O 2  0.5CH 3 OH + 0.5MGLY + 0.7HCHO + 0.5HO2 + 0.3CH 3 C(O)CH 2 OH + 0.2CH 3 C(O)O 2 NO + CH 3 C(O)CH 2 O 2  NO 2 + CH 3 C(O)O 2 + HCHO + HO 2 NO 2 + CH 3 C(O)CH 2 O 2  MPAN CH 3 C(O)CH 3 + hv  CH 3 C(O)O 2 + CH 3 O 2 (p,T dep) CH 3 C(O)CH 3 + hv  CO + products 2 extra tracers, 5 reactions, 1 photolysis rate (2 channels) (Ignore MPAN formation to simplify system, NO 3 reaction too slow) Still debate regarding the photolysis rate although JPL recommendation adopted in TM5

6. 6 Transported tracers InorganicNitrogen and Sulphur Organic C1Higher Organic Misc. O3 O3S H2O2 NOx HNO3 PAN ORGNTR NH3 NH4 SO2 H2SO4 DMS MSA NO3_A CO CH4 HCHO CH3OOH CH3OH HCOOH C2H6 C2H4 C3H8 C3H6 ALD2 ALDx OLE ROOH ISOP TERP MGLY ISPD C2H5OH C2H5OOH MCOOH ACET PAR Rn Pb PSC Modified CBM4 CBMHybrid

7. 7 Sample surface distributions: Methanol and Terpenes Pre-dominantly biogenic sources with large annual fluxes (>100 Tg yr -1 ) Methanol emission covers ~90% of land Terpene emission over forested regions

8. 8 Sample surface distributions Anthropogenic and biomass burning sources for Propene Anthopogenic, BB and biogenic sources for Acetone Surface concentrations seem too low. Too high J values ?? (10 -4 – 10 -5 ) Lifetime of Acetone seems too short as very little leaves the boundary layer: Has been previously measured and modelled in the UTLS

9. 9 UTLS acetone concentrations: CARIBIC vs LMDz-INCA Elias et al, ACP, 2011 [acetone] ranges between 100- 500 pptv at ~250hPa

10. 10 CO surface distribution Surface [CO] ↑ 5-25%. Near background stations ~10% increases. Comparisons against CBM4 show that improvements would occur near VOC sources

11. 11 CO vertical distribution Significant under-prediction of CO in the Free Troposphere using the CBM4 mechanism CBMhybrid improves on this for the free troposphere

12. 12 O 3 surface distribution : July 2001 Norway Netherlands France Spain

13. 13 O 3 vertical distribution Enhances O 3 over-estimation at the summer in the boundary layer at global scale. High differences in the Arctic troposphere during boreal summer +10% differences in the TTL

14. 14 Differences in OH: July 2001 Regional decreases over land; increases over ocean Small increases in BL ; decreases in FT

15. 15 HOx reservoirs TM5 benchmark TM5 online photolysis SCIAMACHY Williams et al, GMDD, 2011

16. 16 NOx reservoirs Large increases in PAN formation accounting for global increase in O 3 Also increases in HNO 3 in large regions Associated decreases in organic nitrate Complex picture of changes in short- lived reactive nitrogen compounds

17. 17 Dampening of nightime oxidation Large decreases in NO 3 over the NO x source regions. Large increases over the oceans (associated with extra PAN transport). No changes in the J value between the simulations ! Loss principally due to repatitioning of reactive nitrogen into PAN/HNO 3. Will also affect N 2 O 5 hydrolysis to HNO 3

18. 18 Conclusions CBMHybrid integrated with online photolysis routine (explicit description of C1-C3 organic compounds included). Surface distributions of species seem ok. The lifetime of acetone appears too short. Reason (sink or source term) has yet to be determined. The global distribution of both CO and O 3 increases in the order of ~5-20%. Coarse comparisions indicate over-estimations of both species in the chemical background at the surface. Improvements in CO in the free-troposphere. Significiant increases in both HO x and NO x reservoirs. Decreases in nightime oxidation over the land due to significant loss of the NO 3 radical. Regional differences in OH distribution (lower over land). Version is currently participating in the Polar Multi-Model intercomparison (MACC II) Budget analysis needs to be performed and compared to that using modified CBM4