1. Processes driving O 3 within the troposphere The Tropics / The Atlantic Bastien Sauvage et al.

2. MOZAIC+SHADOZ (1994-2004) zonal cross section O3 (ppbv) Ozone within the Tropics Martin et al., JGR 2002 O 3 maximum “zonal wave-one” 40W-60E  Observed since the 80’s Logan and Kirchhoff, 1986; Fishman et al. 1987  In the middle upper troposphere  maximum radiative effect (de Forster, 1997) Key role on the oxidizing power of the atmosphere (Jacob et al, JGR 1996)  Attributed to various anthropogenic and natural sources from Fishman et al. 1987… Thompson et al. 2000;2003… to Wang et al 2006 Pressure (hPa) Sauvage et al., JGR 2006 longitude Goal: Quantify what controls tropical O 3 / in the Atlantic? SON TOMS tropospheric O 3 columns (1997) WE

3. (1) Overview Tools Tropospheric ozone chemistry The Tropics: chemical and dynamical context (2) Methodology (3) Model evaluation: -Chemistry : Constraint on lightning and fire emissions -Dynamic (4) What controls the zonal wave one? (5) Conclusions

4. Coupled approach observations/model MOZAIC programme ( Marenco et al., 1998 … Volz-Thomas 2005 ) : 1994-present Automatic measurements O 3, H 2 O + CO, NO y High temporal and spatial resolution and distribution overall O 3 precision ± [2 ppbv]. +26000 Flights In Situ Models Satellite instruments GOME SCIAMACHY OMI Spectrometers backscattered solar radiations O 3 / NO 2 / HCHO OTD/LIS Lightning flashes LAGRANTO FLEXPART Méso-NHGEOS-Chem ACE Fourier Transform Spectrometer/ Solar occultation

5. FiresBiosphereAnthropogenic activity Nitrogen oxides (NO x ) CO, Hydrocarbons Ozone (O 3 ) Hydroxyl (OH) hvhv,H 2 O O 3 production primarily NO x limited Issues: the Tropics (chemistry) STE Tropics: -Higher tropospheric reservoir -Photochemical activity exacerbated (High UV and relative humidity) -Numerous O 3 precursor sources Spatial distribution ~known Uncertainty on emission’s magnitude

6. Soils Natural source : NO x (pulses) through bacterial nitrification Monsoon season: Africa; North India; May-June ~ 70% soil NO x emitted within the Tropics Global production : 4-21 Tg N/yr …uncertain! Issues the Tropics (sources) 1/ Biogenic emissions

7. Emissions: NOx (NO>75%) Lightning density (1995-2004) OTD & LIS Flash number km -2 min -1 DJF JJA Lightning activity mainly located within the Tropics (~65% of Li- NOx) ! Global production : 1-13 Tg N/yr …uncertain! Issues: the Tropics (sources) 2/ lightning emissions (Li-NOx)

8. Source of NO x, VOCs … #fires 2005 (MODIS) NOx: ~70% within the Tropics Global production : 3-13 Tg N/yr …uncertain! Issues: the Tropics (sources) 3/ biomass burning emissions 501001500

9. Issues: the Tropics (sources) 3/ biomass burning emissions: seasonal variations Active fires AVHRR

10. St. Elena H Trades Monsoon East African Low level jet Harmattan Streamlines 850hPa (ECMWF) EQUATORIAL Africa and the Atlantic JANUARY JULY Harmattan St. Elena H Saharan High Trades Issues: Dynamical context Inter tropical front (ITF) Fires

11. Issues: Dynamical context African EJ Tropical Easterly Jet N Hadley S Hadley SW monsoon NE HARMATTAN EQUATOR 10°N20°N 30°N 600hPa 100hPa Schematic circulation over West Africa monsoon season (JJA) ITCZ ITF Sahara Meridional cross section 5°S

12. LAGOS / DJF LAGOS (Gulf of Guinea ) / DJF MOZAIC (1994-2005) MOZAIC data (1994-2005) 600650700750800850900950 Pressure (hPa) u,v <0/Harmattan LAGOS fire pixels (ATSR) 600650700750800850900950 Pressure (hPa) u<0, v=0/AEJ LAGOS fire pixels (ATSR) Sauvage et al., ACP, 2005 Issues: Role of dynamic Pressure (hPa)

13.  Lower tropospheric transport (trades, jets)  affects O 3 distribution (link between emissions and in situ measurements)  Transport and creation of high O 3 and CO concentrations from fires ( >70 ppbv & 500 ppbv in monthly mean!) Sauvage et al., ACP, to be submitted Altitude (km) Meridional baroclinic cells (surface gradients role) T+ /H-T- /H+ latitude Issues: Role of the dynamic Meridional circulation Equivalent potential temperature (K) Méso-NH simulation eeee

14.  Convection ITCZ  Affects O 3 distribution Hadley cells role  redistribution fires + Li-NOx emissions  Convection role in the Tropics 1/ Efficient and rapid vertical redistribution of precursors and species in the UT (longer lifetime) 2/ Global redistribution 3/ HO x impact  UT reactivity O3 meridional gradients MOZAIC transects 300-180hPa Latitude Hadley cells Sauvage et al GRL, in press Issues: Role of the dynamic Europe South Africa

15. Necessity to evaluate emissions and dynamic to better understand what controls O 3 distributions Issues: summary 1/ Important O 3 precursor emissions in the Tropics  But uncertain (intensity / processes) 2/ Importance of dynamics in the Tropics  Lower troposphere (LT) and upper troposphere (UT) transport 3/ Importance of tropospheric ozone in the Tropics  High O3 and precursors concentrations in the LT and UT

16. (1) Overview Tropospheric ozone chemistry Tropics: chemical and dynamical context (2) Methodology (3) Model evaluation: -Chemistry : Constraint on lightning and fire emissions -Dynamic (4) What controls the zonal wave one? (5) Conclusions

17. Methodology Understand O 3 In the Tropics CTM (GEOS-Chem) Original version 1 Constrained Model Quantification (sources / regions) O3 maximum 3 2Constraint and modifications (in situ and satellites)  Lightning: local redistribution OTD-LIS  Soils: NO x a posteriori inventory GOME (Jaeglé et al., Farad., 2005)  Fires: top-down inventory NO x & VOCs / GOME Evaluation O3/RH/CO 4

18. (1) Overview Tropospheric ozone chemistry Tropics: chemical and dynamical context (2) Methodology (3) Model evaluation: -Chemistry : Constraint on lightning and fire emissions -Dynamic (4) What controls the zonal wave one? (5) Conclusions

19. Lightning NOx (Li-NOx) constraint Ozone sensitivity

20. Space-based constraint on Li-NOx spatial distribution Calculation of rescaling factor (R) OTD-LIS climatologies (1995-2004)  spatial lightning redistribution (local approach) for simulated convective events GEOS-Chem simulations exhibited different spatial distribution of lightning compared to satellite -Factors are applied each month for the given season to retain monthly variation -If there is no deep convection in GEOS-Chem, no flashes, R = 1 -No large episodic injection were apparent as convection as low temporal variability

21. Modified version OTD/LIS LiNO x simulated original version -Important regional differences (seasonal latitudinal variation allowed) / Higher oceanic emissions -Same intensity: 6 Tg N yr -1 Space-based constraint on Li-NOx spatial distribution DJF JJA NOx emissions (10 9 molec N/cm 2 /s)

22. In situ data used to evaluate simulation (O3/CO/RH) 1.MOZAIC programme 1994-2005 MOZAIC & SHADOZ sites used for model evaluation 2.SHADOZ ozone sonde network ( Thompson et al., 2003a;b ) : 1998-2004 > 9000 O 3 / RH vertical profiles within the Tropics (30°N-30 ° S)

23. O3 sensitivity to Lightning NOx spatial distribution -O 3 highly sensitive in the MT-UT -O 3 simulations improved by 5-15 ppbv / In situ -Main influence near subsidence areas: South America; Middle East; Atlantic Pressure (hPa) O 3 (ppbv) Original Modified In situ Snapshot of the model evaluation

24. O3 sensitivity to LiNOx intensity 4 TgN/yr; 6 TgN/yr; 8 TgN/yr Evaluation for the Tropics 8Tg N/yr  O 3 over estimation 4Tg N/yr  O 3 under estimation 6±2Tg N/yr  general agreement (including ICARTT results Hudman et al; 2006 ) Pressure (hPa) O 3 (ppbv) Sauvage et al., ACPD 2006 O 3 (ppbv)

25. O 3 sensitivity to LiNO x intensity using different satellite observations 6TgN/yr in agreement with model/satellite study NO 2 /HNO 3 /O 3 Martin et al., JGR, in press  6±2Tg N/yr NO 2 SCIAMACHY O 3 OMI HNO 3 (ACE) HNO 3 (pptv) WE Model 6TgN/yr 4TgN/yr 8TgN/yr Annual meridional mean HNO 3 (200-350hPa) Simulated HNO 3 / LiNO x between 4 and 8TgN/yr longitude No lightning No wave-one pattern

26. Biomass burning emissions constraint O 3 sensitivity Savanna fires (SAFARI 2000)

27. How to use remote-sensed data to constrain emissions? NO h O3O3 NO 2 HNO 3 Lifetime hours VOC OH HCHO h hours CO hours PBL Emissions NO x VOC Free troposphere NO NO 2 O 3, HO 2 hv HNO 3 NOx lifetime ~ week O3O3 lifetime ~ month O3O3 lifetime ~ hours Tropospheric NO 2 column ~ E NOx Tropospheric HCHO column ~ E VOC GOME: 320x40 km 2

28. GOME NO 2 original model NO 2 Constrained model NO 2 Better agreement during biomass burning season 10 15 molec cm -2 NO x emissions / Tropics: 4.8TgN/yr  5.8TgN/yr DJF MAM JJA SON Space-based constraint on biomass burning emissions: NO x Better spatial correlations between GOME and model NO 2 columns R 2 > 0.86

29. Space-based constraint on biomass burning emissions: VOC GEOS-Chem tropospheric HCHO presented systematic bias with GOME over biomass burning region GEOS-Chem original (Andreae and Merlet 2001) Andreae compilation (2005) (Bertschi et al. 2003…Yokelson et al., 2003) Alkenes0.3g/kg 1.4  0.6 g/kg HCHO0.36g/kg 0.7  0.4g/kg 1-Evidence of higher reactive VOC EF from literature Tentatively attribute bias to HCHO and alkenes biomass burning emissions

30. Seasonal HCHO tropospheric columns (10 16 molecules/cm 2 ) GOME 2000 GEOS-Chem with MEGAN 2000 2-Bias not corrected using MEGAN Space-based constraint on biomass burning emissions: VOC  Use of GOME HCHO to constrain VOC over biomass burning regions

31. GOME HCHO  fires VOC emissions : HCHO and alkenes increased x 2 GOME HCHOContrained model HCHOoriginal model HCHO Space-based constraint on biomass burning emissions: VOC Better spatial correlations between GOME and model HCHO columns R 2 > 0.7 Better agreement during biomass burning season

32. O3 (ppbv) Pressure (hPa) Top-down improves lower tropospheric O3 from 5-20 ppbv during biomass burning season Main influence over Africa DJF-JJA; India MAM O 3 sensitivity to fire emissions (NOx and VOCs)  Original  Constraint  In Situ Model problems in reproducing meso scale processes (monsoon flow) Lagos Nigeria DJF Abidjan Ivory Coast DJF Congo-Brazzaville JJA Pressure (hPa)

33. Dynamic sensitivity

34. Convection effect GEOS3/GEOS4 GEOS3GEOS4 1.Convection Weak divergence - + 2.Cloud Top Height +- 3.Cloud Optical Depth +- Folkins et al., 2006 Detrainment and entrainment (upward+downward) / cloudy column 20S-20N Deep outflow layer GEOS4 Convection affects vertical distribution of species, especially in the outflow detrainment entrainment Liu et al; 2006; Wu et al;2006;

35. Role of convection: Role of convection: chemical species as convection tracers MOZAIC transect Latitude (25S-25N) Convection tracers (ITCZ) O 3 - / RH + / CO +  GEOS3 weak deep outflow / Weak convective detrainment CO (ppbv) O3 (ppbv) RH (%) MOZAIC GEOS4 GEOS3 ITCZ Further comparison with daily flights

36. GEOS3 vs GEOS4  GEOS3 weak deep outflow  Convection affects ozone but also Li-NOx does (vertical placement) and radiative effect (photolysis frequencies) Pressure (hPa) Ozone (ppbv)RH (%) In situ GEOS 4 GEOS 3

37. 3. What controls O3 maximum in the Atlantic? O 3 maximum ?

38. Atlantic O 3 budget/ Sensitivity to sources O 3 sensitivity to NO x emissions  NO x decreased by 1% for each source (non linear chemistry) ΔDU Lightning  main tropical and Atlantic influence / Surface sources  local influence DJF Influence on the Atlantic (no emissions): LiNOx: >36% tropical Atlantic O 3 Soils >7%; Fires > 9% …half of lightning (despite similar NOx intensity) ’Background’ 30% SON ΔO 3 tropospheric Lightning Ozone Production Efficiency (OPE)= 3 time each surface source OPE 4TgN/yr3TgN/yr5TgN/yr

39. ΔDU >20%>15%>6% DJF MAM JJA SON ΔO 3 tropospheric Atlantic O 3 budget / sensitivity to regions Sensitivity to decreasing NO x emissions by 1% over regions

40. “zonal-wave one” “zonal-wave one” Zonal/Vertical cross-section / O 3 (ppbv) O 3 flux (kg/s) DJF MAM JJA SON subsidence AfricaSouth Am.

41. Dynamic of the O 3 maximum O3O3 ppb NO x ppb 3/O 3 buildup during transport and subsidence over South Atlantic high area Zonal transport 1/Surface emissions of O 3 precursors S. Am.Africa 2/Injection of NOx into the MT-UT with lightning emissions and uplift into ITCZ Model 2000 SHADOZ+ MOZAIC 1994-2005 O 3 (ppbv) 4/ zonal transport Meridional Transport AFRICAATLANTIC SN O 3 (ppbv)

42. Oxidizing capacity of the tropical troposphere Tropical OHΔOH lightning ΔOH surface Annual mean 10 6 molec cm -3 s -1 ) 1.510.540.40 Spivakovsky et al. (2000): Tropical OH: 1.41 10 6 molec cm -3 s -1 (climatologies)  Model over estimation by 6% LiNOx dominates oxidizing capacity within the Tropics (>35% vs >26% for total surface sources)

43. EAST AFRICA South America > 21%> 36%NO x surface sourcesSTE ~ 6% Conclusions: processes driving the O 3 max Engine: convergence & subsidence Fuel: in majority Li-NO x, with higher OPE >6% >20% >15%

44. Acknowledgements : Randall V. Martin, Aaron van Donkelaar, Ian Folkins, Dalhousie University Paul I. Palmer, Edinburgh University Kelly Chance, Xiong Liu Harvard-Smithsonian May Fu, Shiliang Wu, Bob Yantosca and all the GEOS-Chem community Harvard University MOZAIC team, LA, FZJ Meinrat.O. Andreae, MPI Dennis Boccippio, Jerry Ziemke, NASA Anne M. Thompson, Pennsylvania University Peter Bernath, Toronto University Lyatt Jaeglé, Washington University Supported by NASA atmospheric composition program