1. Constraints on the Production of Nitric Oxide by Lightning as Inferred from Satellite Observations Randall Martin Dalhousie University With contributions from Bastien Sauvage & Ian Folkins: Dalhousie Univeristy Christopher Sioris: University of Saskatchewan Christopher Boone and Peter Bernath: University of Waterloo Jerry Ziemke: NASA Goddard

2. Global Lightning NOx Source Remains Uncertain Constrain with Top-down Satellite Observations SCIAMACHY Tropospheric NO 2 Columns ACE-FTS Limb HNO 3 Measurements in the Upper Troposphere OMI & MLS Both instruments onboard Aura satellite Tropospheric O 3

3. Current Estimate of Annual Global NOx Sources As Used In GEOS-Chem 10 10 molecules N cm -2 s -1 Lightning Global: 6.0 Tg N yr -1 Tropics: 4.4 Tg N yr -1 Other NOx sources: (fossil fuel, biofuel, biomass burning, soils) 39 Tg N yr -1

4. Tropospheric NO 2 Columns Retrieved from SCIAMACHY Retrieval Uncertainty ±(5x10 14 molec cm -2 + 30%) Tropospheric NO 2 (10 15 molecules cm -2 ) Nov - Apr May - Oct NO / NO2   w Altitude Data from Martin et al., 2006

5. Simplified Chemistry of Nitrogen Oxides Exploit Longer Lifetimes in Upper Troposphere NO NO 2 NOx lifetime < day Nitrogen Oxides (NO x ) Boundary Layer NO / NO2   with altitude hv NO NO 2 O 3, RO 2 hv HNO 3 NOx lifetime ~ week lifetime ~ weeks Ozone (O 3 ) lifetime ~ month Upper Troposphere Ozone (O 3 ) lifetime ~ days HNO 3 O 3, RO 2

6. Strategy 1) Use GEOS-Chem model to identify species, regions, and time periods dominated by the effects of lightning NOx production 2) Constrain lightning NOx source by interpreting satellite observations in those regions and time periods

7. Simulated Monthly Contribution of Lightning, Soils, and Biomass Burning to NO 2 Column

8. Tropospheric NO 2 (10 14 molec cm -2 ) Annual Mean NO 2 Column at Locations & Months with >60% from Lightning, 60% from Lightning, <25% from Surface Sources Meridional Average SCIAMACHY (Uses 15% of Tropical Observations) GEOS-Chem with Lightning (8% bias, r=0.75) GEOS-Chem without Lightning (-60% bias) NO 2 Retrieval Error ~ 5x10 14 molec cm -2 GEOS-Chem with Lightning (6±2 Tg N yr -1 ) SCIAMACHY GEOS-Chem without Lightning

9. ACE HNO 3 over 200-350 hPa for Feb 2004 – Feb 2006 HNO 3 Mixing Ratio (pptv) Data from Boone et al., 2005

10. GEOS-Chem Calculation of Contribution of Lightning to HNO 3 HNO 3 from LightningFraction from Lightning Focus on 200-350 hPa HNO 3 With Lightning (6±2 Tg N yr -1 ) No Lightning Fraction of HNO 3 from Lightning Jan Jul

11. Annual Mean HNO 3 Over 200-350 hPa at Locations & Months with > 60% of HNO 3 from Lightning Meridional Average ACE (Uses 83% of Tropical Measurements) GEOS-Chem with Lightning (-12% bias, r=0.75) GEOS-Chem without Lightning (-80% bias) HNO 3 Mixing Ratio (pptv) ACE-FTS GEOS-Chem with Lightning (6±2 Tg N yr -1 ) GEOS-Chem without Lightning HNO 3 Retrieval Error ~35 pptv

12. OMI/MLS Tropospheric Ozone Column Jan Jul Data from Ziemke et al. (2006)

13. Calculated Monthly Contribution of Lightning to O 3 Column O 3 Column from LightningColumn Fraction from Lightning

14. Annual Mean Tropospheric O 3 Columns at Locations & Months with > 40% of Column from Lightning Meridional Average OMI/MLS (Uses 15% of Tropical Measurements) GEOS-Chem with Lightning (-1% bias, r=0.85) GEOS-Chem without Lightning (-45% bias) Tropospheric O 3 (Dobson Units) OMI/MLS GEOS-Chem with Lightning (6±2 Tg N yr -1 ) GEOS-Chem without Lightning O 3 Retrieval Error < 5 Dobson Units

15. Conclusions Global lightning NOx source likely between 4 – 8 Tg N / yr 6 Tg N / yr is a best estimate Further refinement will require - stronger constraints on midlatitude source - improved satellite retrieval accuracy (e.g. NO 2 ) - more observations (e.g. HNO 3 ) - model development to better represent processes (e.g. lightning NOx representation, vertical transport) Acknowledgements Supported by NASA’s Radiation Science Program