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Space-based Insight into Global Nitrogen Oxides and Tropical Tropospheric Ozone

This study provides space-based insights into the sources of nitrogen oxides (NOx) and their implications for tropical tropospheric ozone. The research uses satellite observations and modeling to evaluate and improve global NOx emission inventories.

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Space-based Insight into Global Nitrogen Oxides and Tropical Tropospheric Ozone

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  1. Space-based insight into the global sources of nitrogen oxides with implications for tropical tropospheric ozone Randall Martin Dalhousie University With contributions from Bastien Sauvage, Neil Moore, Thomas Walker: Dalhousie University Christopher Sioris: Environment Canada Christopher Boone and Peter Bernath: University of Waterloo Jerry Ziemke: NASA Goddard Lyatt Jaegle: University of Washington Xiong Liu, Kelly Chance: Harvard-Smithsonian Center for Astrophysics

  2. Stratopause Tropopause Tropospheric Ozone is a Key Species in Climate and Air Quality • Major greenhouse gas • Largely controls atmospheric oxidation • Primary constituent of smog Mesosphere Stratosphere Ozone layer Half of all Americans live in regions that exceed the surface ozone standard Troposphere

  3. Global Budget of Tropospheric Ozone Driven By Production in the Troposphere Ozone Production is Largely NOx-Limited hv hv,H2O Nitrogen oxides (NOx) CO, Volatile Organic Compounds (VOCs) Ozone (O3) Hydroxyl (OH) Fires Biosphere Human activity

  4. How Do We Evaluate and Improve A Priori Bottom-up Inventories? Bottom-up Estimates for Global NOxEmissions (Range) in Tg N yr-1 for 2000 Fossil Fuel 24 (20-33) Biomass Burning 6 (3-13)Soils 7 (4-21)Lightning 6 (1-20)

  5. Top-Down Information from Satellite Observations • Nadir-viewing solar backscatter instruments including ultraviolet and visible wavelengths • GOME 1995-2003 • Spatial resolution 320x40 km2 • Global coverage in 3 days • SCIAMACHY 2002-present • Spatial resolution 60x30 km2 • Global coverage in 6 days • OMI 2004-present • Spatial resolution up to 13x24 km2 • Daily global coverage • GOME-2 2006-present • Spatial resolution up to 40x80 km2 • Daily global coverage

  6. Retrieve NO2 Columns To Map Surface NOx Emissions NOx = NO + NO2 Tropospheric NO2 column ~ ENOx BOUNDARY LAYER hv NO2 NO/NO2  W ALTITUDE NO O3 lifetime <1 day HNO3 Emission NITROGEN OXIDES (NOx)

  7. Spectral Fit of NO2 Solar Io Distinct NO2 Spectrum Ozone Backscattered intensity IB NO2 Scattering by Earth surface and by atmosphere Albedo A O2-O2 Nonlinear least-squares fitting Fitting Uncertainty 5-10x1014 molec cm-2 Martin et al., JGR, 2002, 2006

  8. Total NO2 Slant Columns Observed from SCIAMACHY Dominant stratospheric background (where NO2 is produced from N2O oxidation)Also see tropospheric hot spots (fossil fuel and biomass burning) May-October 2004 Uncertainty in Stratospheric Removal 2-10x1014 molec cm-2

  9. Perform an Air Mass Factor (AMF) Calculation to Account for Viewing Geometry and Scattering Cloud Radiance Fraction IB,c / (IB,o + IB,c) IB,c IB,o • GOMECAT (Kurosu) & FRESCO Clouds Fields [Koelemeijer et al., 2002] • Surface Reflectivity [Koelemeijer et al., 2003] • LIDORT Radiative Transfer Model [Spurr et al., 2002] • GEOS-CHEM NO2 & aerosol profiles Io q Rc Ro Pc AMF Uncertainty40% dt Rs Martin et al., JGR, 2002, 2003, 2006

  10. Cloud-filtered Tropospheric NO2 Columns Retrieved from SCIAMACHY Mean Uncertainty ±(5x1014 + 30%) NO/NO2  W ALTITUDE May 2004 – Apr 2005 Martin et al., JGR, 2006

  11. ICARTT Campaign Over and Downwind of Eastern North America in Summer 2004 Aircraft Flight Tracks and Validation LocationsOverlaid on SCIAMACHY Tropospheric NO2 Columns NASA DC-8 NOAA WP-3D

  12. GEOS-Chem Chemical Transport Model 41 tracers ~90 species 300 reactions • Assimilated Meteorology (NASA GMAO) • 2ox2.5o horizontal resolution, 30 vertical layers • O3-NOx-VOC chemistry • SO42--NO3--NH4+-H2O, dust, sea-salt, organic & elemental carbon aerosols • Interactive aerosol-chemistry Solve continuity equation for individual gridboxes • Sources: • emissions • chemical prod. Sinks: - chemical loss - deposition Transport flux divergence Accumulation Dx ~ 200 km Dz ~ 1 km

  13. Air Mass Factor Calculation in SCIAMACHY Retrieval Needs External Info on Shape of Vertical Profile Increased Lightning NOx Emissions Improves GEOS-CHEM Simulation of Midlatitude NO2 Profiles Remaining Discrepancy In Vertical Profile of NOx Emissions In Situ 0.4 Tg N yr-1 1.6 Tg N yr-1 Midlatitude lightning Mean Bias in AMF: 0.4 Tg N yr-1 12% 9% 3% 1.6 Tg N yr-1 1% 5% 3% Martin et al., JGR, 2006

  14. Enhanced Midlatitude Lightning Reduces Discrepancy with SCIAMACHY over North AtlanticProfile of NOx Emissions (lifetime) Contributes to Remaining Discrepancy SCIAMACHY NO2 (1015 molec cm-2) GEOS-Chem NO2 (1015 molec cm-2) 1.6 Tg N in Midlat GEOS-Chem NO2 (1015 molec cm-2) 0.4 Tg N in Midlat Martin et al., JGR, 2006 May-Oct 2004

  15. Significant Agreement Between Coincident Cloud-Filtered SCIAMACHY and In-Situ Measurements r = 0.77 slope = 0.82 1:1 line Cloud-radiance fraction < 0.5 In-situ measurements below 1 km & above 3 km Assume constant mixing ratio below lowest measurement Add upper tropospheric profile from mean obs Cohen (DC-8) Ryerson (WP-3D) Horizontal bars show 17th & 83rd percentiles Martin et al., JGR, 2006

  16. Conduct a Chemical Inversion For NOx Emissions min cost function A Priori NOx Emissions (xa) SCIAMACHY NO2 Columns (y) 1011 molec N cm-2 s-1 1015 molec N cm-2 GEOS-CHEM model F(x) Sa A posteriori emissions x Error weighting Top-Down Emissions Sy

  17. Significant Agreement Between A Priori and A PosterioriLargest Discrepancy in East Asia and Major Urban Centers (2000) r2=0.82 Martin et al., JGR, 2006

  18. A Posteriori NOx Emissions from East Asia Exceed Those from Either North America or EuropeImplications for North American Air Quality A priori (38 Tg N/yr) A posteriori (46 Tg N/yr) Martin et al., JGR, 2006

  19. INTEX-B: Long-Range Transport to North AmericaAverage over April – May 2006 Ozone Column (Dobson Units) ΔOzone Column (Dobson Units) Sensitivity to Asian Emissions Sensitivity to Lightning Whistler, BC Sensitivity at 750 hPa to PAN ΔOzone (ppbv) standard No Asian NOx No lightning Thomas Walker

  20. Direct Retrieval of Tropospheric Ozone from GOMEUsing Optimal Estimation in Ultraviolet with TOMS V8 a priori GOME GEOS-CHEM Tropospheric Ozone Column (Dobson Units) Liu et al., JGR, 2006

  21. In Situ Data Used for Tropical Evaluation 1.MOZAIC programme 1994-2005 2.SHADOZ ozone sonde network (Thompson et al., 2003a;b): 1998-2004 MOZAIC & SHADOZ sites used for model evaluation > 9000 vertical profiles within the Tropics (30°N-30°S)

  22. Northern Tropics Remain a Challenge for Satellites and ModelsScan-Angle Method (Kim et al., 2005) UV Method That Best Captures In Situ Seasonal Variation Comparison with MOZAIC Ozone Measurements Liu et al., JGR, 2006

  23. Fuel Combustion 1. Spatial location of FF-dominated regions in a priori (>90%) 1 2 Biomass Burning 2. Spatiotemporal distribution of fires used to separate BB/soil VIRS/ATSR fire counts Soils No fires + background Algorithm for partitioning top-down NOx inventory (2000) GOME NOx emissions 8.9 Algorithm tested using synthetic retrieval Jaeglé et al., 2005

  24. Largest soil emissions: seasonally dry tropical + fertilized cropland ecosystems Speciated Inventory for Soil emissions A posteriori 70% larger than a priori! A priori A posteriori r2= 0.62 (±90%) (±200%) North Eq. Africa East Asia Soils Soils Onset of rainy season: Pulsing of soil NOx! Jaeglé et al., 2005

  25. Improved Bottom-up Inventoryfor Soil NOx Emissions Developments of soil temp/soil moisture, pulsing, fertilizer application Change in NOx Emissions Soil NOx Emissions molec cm-2 s-1 Δ molec cm-2 s-1 Δ Global Total = +1.9 Tg N/yr Global Total = 7.8 Tg N/yr Neil Moore

  26. Top-down Constraint on Biomass Burning NOx Emissions GOME Model constrained Model original DJF MAM NO2 Column (1015 molec cm-2) Observed Improved simulation of lower tropospheric O3 versus aircraft measurements Pressure (hPa) Top-down Bottom-up Sauvage et al., ACP, 2007 O3 Mixing Ratio (ppbv)

  27. Global Lightning NOx Source Remains UncertainConstrain with Top-down Satellite Observations SCIAMACHY Tropospheric NO2 Columns ACE-FTS Limb HNO3 Measurements in the Upper Troposphere OMI & MLS Tropospheric O3 10-year Mean Flash Rate from the OTD & LIS Satellite Instruments Global rate 44±5 flash/sec [Christian et al. 2003] 30 – 500moles NO per flash Flashes km-2 min-1

  28. Current Estimate of Annual Global NOx SourcesAs Used In GEOS-Chem 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 1010 molecules N cm-2 s-1

  29. Simplified Chemistry of Nitrogen OxidesExploit Longer Lifetimes in Upper Troposphere Upper Troposphere hv NO Ozone (O3) NO2 O3,RO2 lifetime ~ month NOx lifetime ~ week HNO3 lifetime ~ weeks NO/NO2  with altitude Boundary Layer hv NO2 Ozone (O3) NO O3,RO2 lifetime ~ days NOx lifetime < day HNO3 Nitrogen Oxides (NOx)

  30. 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

  31. Simulated Monthly Contribution of Lightning, Soils, and Biomass Burning to NO2 Column

  32. Annual Mean NO2 Column at Locations & Months with >60% from Lightning, <25% from Surface Sources SCIAMACHY (Uses 15% of Tropical Observations) Meridional Average GEOS-Chem with Lightning (6±2 Tg N yr-1) SCIAMACHY GEOS-Chem with Lightning (8% bias, r=0.75) GEOS-Chem without Lightning (-60% bias) GEOS-Chem without Lightning NO2 Retrieval Error ~ 5x1014 molec cm-2 Tropospheric NO2 (1014 molec cm-2) Martin et al., 2007

  33. ACE HNO3 over 200-350 hPa for Feb 2004 – Feb 2006 HNO3 Mixing Ratio (pptv) Data from Boone et al., 2005

  34. GEOS-Chem Calculation of Contribution of Lightning to HNO3 HNO3 With Lightning (6±2 Tg N yr-1) Focus on 200-350 hPa Fraction of HNO3 from Lightning No Lightning HNO3 from Lightning Fraction from Lightning Jan Jul

  35. Annual Mean HNO3 Over 200-350 hPa at Locations & Months with > 60% of HNO3 from Lightning ACE (Uses 83% of Tropical Measurements) Meridional Average GEOS-Chem with Lightning (6±2 Tg N yr-1) ACE-FTS GEOS-Chem with Lightning (-12% bias, r=0.75) GEOS-Chem without Lightning GEOS-Chem without Lightning (-80% bias) HNO3 Retrieval Error ~35 pptv Martin et al., 2007 HNO3 Mixing Ratio (pptv)

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

  37. Calculated Monthly Contribution of Lightning to O3 Column O3 Column from Lightning Column Fraction from Lightning Martin et al., 2007

  38. Annual Mean Tropospheric O3 Columns at Locations & Months with > 40% of Column from Lightning OMI/MLS (Uses 15% of Tropical Measurements) Meridional Average GEOS-Chem with Lightning (6±2 Tg N yr-1) GEOS-Chem with Lightning (-1% bias, r=0.85) OMI/MLS GEOS-Chem without Lightning (-45% bias) GEOS-Chem without Lightning O3 Retrieval Error < 5 Dobson Units Martin et al., 2007 Tropospheric O3 (Dobson Units)

  39. Spatial Distribution of GEOS-Chem Lightning NOx Source Local Scaling to Match 10-year HRAC Seasonal OTD-LIS Climatology Scaled version Original version DJF DJF JJA JJA Lightning NOx emissions (109 molec N cm-2 s) Same intensity: 6 Tg N yr-1 Sauvage et al., ACP, 2007

  40. Ozone Sensitivity to Spatial Distribution of Lightning NOx Snapshot of the model evaluation Original Modified In situ Scaled Pressure (hPa) Pressure (hPa) O3 (ppbv) O3 (ppbv) -O3 highly sensitive in the MT-UT -O3 simulations improved by 5-15 ppbvversus In situ -Main influence near subsidence areas: South America; Middle East; Atlantic Sauvage et al., ACP, 2007

  41. Ozone sensitivity to Lightning NOx 4 TgN/yr; 6 TgN/yr; 8 TgN/yr Scaled Scaled Scaled Pressure (hPa) Pressure (hPa) O3 (ppbv) Evaluation for the Tropics 8Tg N/yr  O3 over estimation 4Tg N/yr  O3under estimation 6±2Tg N/yrgeneral agreement Sauvage et al., ACP, 2007 O3 (ppbv)

  42. Lightning NOx Dominant Source for Tropical Tropospheric Ozone Sensitivity to decreasing NOx emissions by 1% for each source 6 Tg N/yr 6 Tg N/yr DJF 6 Tg N/yr MAM JJA SON ΔDU Lightning Ozone Production Efficiency = 3 times OPE of each surface source Atmospheric OxidationLargely Controlled by Lightning NOx Source Sauvage et al., JGR, in press

  43. S. Am. Africa NOx ppb 1/Surface emissions of O3 precursors 2/Injection of NOx (mostly from lightning) into the upper troposphere 3/O3 production during transport and subsidence over South Atlantic basin Simulated Annual Mean Characteristics O3 ppb Sauvage et al., JGR, in press

  44. Conclusions Growing confidence in top-down constraints on NOx emissions South Atlantic Maximum largely results from lightning NOx due to high ozone production efficiency Global lightning NOx source likely between 4 – 8 Tg N / yr 6 Tg N / yr is a best estimate Further refinement of lightning source will require - stronger constraints on midlatitude source - improved satellite retrieval accuracy (e.g. NO2) - more observations (e.g. HNO3) - model development to better represent processes (e.g. lightning NOx representation, vertical transport) Acknowledgements Supported by NASA, CFCAS, and NSERC

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