1. A multi-model analysis of the tropospheric ozone budget David Stevenson 1, F.J. Dentener 2, M.G. Schultz 3, K. Ellingsen 4, T.P.C. van Noije 5, O. Wild 6, G. Zeng 7, M. Amann 8, C.S. Atherton 9, N. Bell 10, D.J. Bergmann 9, I. Bey 11, T. Butler 12, J. Cofala 8, W.J. Collins 13, R.G. Derwent 14, R.M. Doherty 1, J. Drevet 11, H.J. Eskes 5, A.M. Fiore 15, M. Gauss 4, D.A. Hauglustaine 16, L.W. Horowitz 15, I.S.A. Isaksen 4, M.C. Krol 2, J.- F. Lamarque 17, M.G. Lawrence 12, V. Montanaro 18, J.-F. Müller 19, G. Pitari 18, M.J. Prather 20, J.A. Pyle 7, S. Rast 3, J.M. Rodriguez 21, M.G. Sanderson 13, N.H. Savage 7, D.T. Shindell 10, S.E. Strahan 21, K. Sudo 6, and S. Szopa 16 1. University of Edinburgh, School of GeoSciences, Edinburgh, United Kingdom. 2. Joint Research Centre, Institute for Environment and Sustainability, Ispra, Italy. 3. Max Planck Institute for Meteorology, Hamburg, Germany. 4. University of Oslo, Department of Geosciences, Oslo, Norway. 5. Royal Netherlands Meteorological Institute (KNMI), Atmospheric Composition Research, De Bilt, the Netherlands. 6. Frontier Research Center for Global Change, JAMSTEC, Yokohama, Japan. 7. University of Cambridge, Centre of Atmospheric Science, United Kingdom. 8. IIASA, International Institute for Applied Systems Analysis, Laxenburg, Austria. 9. Lawrence Livermore National Laboratory, Atmos. Science Div., Livermore, USA. 10. NASA-Goddard Institute for Space Studies, New York, USA. 11. Ecole Polytechnique Fédéral de Lausanne (EPFL), Switzerland. 12. Max Planck Institute for Chemistry, Mainz, Germany. 13. Met Office, Exeter, United Kingdom. 14. rdscientific, Newbury, UK. 15. NOAA GFDL, Princeton, NJ, USA. 16. Laboratoire des Sciences du Climat et de l'Environnement, Gif-sur-Yvette, France. 17. National Center of Atmospheric Research, Atmospheric Chemistry Division, Boulder, CO, USA. 18. Università L'Aquila, Dipartimento di Fisica, L'Aquila, Italy. 19. Belgian Institute for Space Aeronomy, Brussels, Belgium. 20. Department of Earth System Science, University of California, Irvine, USA 21. Goddard Earth Science & Technology Center (GEST), Maryland, Washington, DC, USA.

2. Tropospheric ozone budget Ozone is an important greenhouse gas and air pollutant Ozone budget and lifetime crucial for: –Long-range transport –Global Warming Potentials –Oxidising capacity –Climate-Chemistry (radiative forcing and feedbacks) Previous intercomparisons (e.g. IPCC TAR literature survey) of modelled tropospheric ozone budget hampered by: –Definition of P O3 and L O3 –Definition of troposphere –Differences in emissions What we really want to understand are differences due to model formulation (chemistry, convection, resolution, mixing, boundary conditions…)

3. Defining the O 3 or O x budget NO 2 L: O 3 + HO 2 O 3 + OH O( 1 D) + H 2 O O 3 + alkenes O 3 deposition O 3 O( 3 P) O( 1 D) Stratospheric input PAN HNO 3 HO 2 NO 2 NO 3 N2O5N2O5 dep NO P: NO + RO 2 + other net loss terms Some studies use wider definition; should make only minor difference Different model chemical schemes – potential source of differences

4. ACCENT Intercomparison Prescribed anthropogenic emissions –but modellers used their own natural emissions, so still some emissions uncertainty Defined O 3 budget terms –but some modellers used their own definitions, specific to chemical scheme –requested 3D monthly mean P and L –also O 3 deposition; inferred stratospheric input Defined tropopause O 3 =150 ppbv –centralised analysis

5. 20 Models supplied O 3 budgets CHASER_CTM CHASER_GCM FRSGC/UCI GEOS-CHEM GMI/CCM3 GMI/DAO GMI/GISS LLNL-IMPACT LMDz/INCA-CTM LMDz/INCA-GCM MOZ2-GFDL MOZART4 MOZECH MOZECH2 STOCHEM-HadAM3 STOCHEM-HadGEM TM4 TM5 ULAQ UM_CAM CTMs driven by analyses CTMs driven by GCM output CTMs coupled to GCMs

6. Year 2000 Tropospheric O 3 budget Tg(O 3 )/yr PLDS inf B/Tg(O 3 )  /days ACCENT51004670100055034022 IPCC TAR 34203470770 30024

7. Zonal Annual Mean Ozone chemical production Relatively high values through whole troposphere Relatively low values in tropical UT Differences at poles Ozone chemical production mainly reflects NO x distributions

8. Zonal Annual Mean Ozone chemical destruction Ozone chemical destruction mainly reflects H 2 O distribution (also O 3 distribution)

9. Zonal Annual Mean Ozone net chemical production

10. Surface level O 3 Net Chemical Production

11. Multi-model ensemble mean ozone P, L, NCP  = 0.997 Surface Ship NO x

12. Multi-model ensemble mean ozone P, L, NCP  = 0.975

13. Multi-model ensemble mean ozone P, L, NCP  = 0.930

14. Multi-model ensemble mean ozone P, L, NCP  = 0.870

15. Multi-model ensemble mean ozone P, L, NCP  = 0.792 Mid-trop net destruction

16. Multi-model ensemble mean ozone P, L, NCP  = 0.700 Mid-trop net destruction

17. Multi-model ensemble mean ozone P, L, NCP  = 0.600 Mid-trop net destruction

18. Multi-model ensemble mean ozone P, L, NCP  = 0.505

19. Multi-model ensemble mean ozone P, L, NCP  = 0.422

20. Multi-model ensemble mean ozone P, L, NCP  = 0.355 Upper-trop net production lightning

21. Multi-model ensemble mean ozone P, L, NCP  = 0.300 Upper-trop net production lightning

22. Multi-model ensemble mean ozone P, L, NCP  = 0.250 Upper-trop net production lightning

23. Multi-model ensemble mean ozone P, L, NCP  = 0.200 Upper-trop net production lightning

24. Multi-model ensemble mean ozone P, L, NCP  = 0.150 Upper-trop net production lightning

25. Multi-model ensemble mean ozone P, L, NCP  = 0.099 Upper-trop net production lightning

26. Global O 3 budget terms O 3 lifetime / days O 3 burden / Tg(O 3 ) Results for a single model, several scenarios Colours signify different models Ensemble mean model (offset) Higher burden goes with longer lifetime Climate change shortens lifetime but burden can rise/fall As emissions rise, burden increases, lifetime falls MFR A2

27. Conclusions First well-constrained analysis of several model’s ozone budgets, with consistent definitions of budget terms, tropospheric domain, and anthropogenic emissions Broadly consistent gross features Production reflects NO x distribution Destruction reflects H 2 O (and O 3 ) distribution Some inter-model differences in lightning NO x /convection; isoprene; H 2 O; polewards transport; BL Quite large differences compared to IPCC TAR –NO x and isoprene emissions –Stratospheric input Deposition also crucial; most of the O 3 budget is in BL

28. Further information Dentener et al., in press, Env. Sci. Tech. –Overview of intercomparison Stevenson et al., in press, JGR –Tropospheric O 3 and CH 4 Van Noije et al., in press, ACPD –NO 2 columns, modelled & GOME Shindell et al., submitted, JGR –CO, modelled & MOPITT Dentener et al., submitted, GBC –Deposition of N and S Ellingsen et al., in prep. –Surface O 3 air quality +probably more dstevens@staffmail.ed.ac.uk