Tropospheric NO2 columns as a Top-down Constraint on NOx Emission Inventories Randall Martin Dalhousie University Harvard-Smithsonian Center for Astrophysics With contributions from Lok Lamsal, Neil Moore, Bastien Sauvage: Dalhousie Univeristy Christopher Sioris: Environment Canada Rob Pinder: US EPA

Uncertainty in Emissions Remains a Major Weakness in Current Models Estimates of Global NOx Emissions (Range) in Tg N yr-1 for 2000 Fossil Fuel 25 (21-28) Biomass Burning 6 (3-10) Soils 6 (4-17) Lightning 6 (2-8)

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)

Conduct a Chemical Inversion For NOx Emissions Need Information on NOx Lifetime, NOx to NO2 Column, Transport SCIAMACHY NO2 Columns A Priori NOx Emissions 2004-2005 1011 molec N cm-2 s-1 1015 molec N cm-2 GEOS-CHEM model A posteriori emissions Top-Down Emissions

Local Relationship Between NOx Emissions and NO2 Columns Can Assume Linearity Around A Priori January o Nonlinear __ Linear July * Nonlinear --- Linear Martin et al., JGR, 2006

Significant Agreement Between A Priori and A Posteriori Largest Discrepancy in Rapidly Developing Regions (2000) r2=0.82 Most Recent Edgar Emissions for 2000 Martin et al., JGR, 2006

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

Bottom-up Inventory for 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 Global Total = 7 Tg N/yr Neil Moore

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

Large Differences in NO2 Columns Reduced With Revised AMF Eastern China BIRA/KNMI BIRA/KNMI + Dalhousie AMF Tropospheric NO2 (1015 molec/cm2) van Noije et al., 2006 Aaron van Donkelaar

NOx emissions Inferred from OMI DJF MAM JJA SON Priori = 40 Tg N, Std – 61 Tg, r=0.86; nrt = 53Tg, r=0.88 Lok Lamsal

Seasonal Variation in Inferred Emissions OMI (standard) OMI (NRT) A priori (NEI2002) OMI (standard) OMI (NRT) A priori (EMEP2003) March 2006 – Feb 2007 Lok Lamsal

Ongoing Work at Higher Resolution Accurate Representation of the Free Troposphere Remains a Challenge SCIAMACHY CMAQ CMAQ (<2km) + GEOS-Chem (>2km) June - August 2004 Rob Pinder

Air Mass Factor Calculation in NO2 Retrieval Needs External Info on Shape of Vertical Profile Increased Lightning NOx Emissions Improves GEOS-CHEM Simulation of Midlatitude NO2 Profiles Remaining Discrepancy: Profile of 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

Enhanced Midlatitude Lightning Reduces Discrepancy with SCIAMACHY over North Atlantic Remaining Discrepancy: Profile of NOx Emissions (lifetime) 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 May-Oct 2004 Martin et al., JGR, 2006

Global Lightning NOx Source Remains Poorly Constrained 10-year Mean Flash Rate from the OTD & LIS Satellite Instruments Global rate 44±5 flash/sec [Christian et al. 2003] DJF 30 – 500 moles NO per flash JJA Flashes km-2 min-1

Current Estimate of Annual Global NOx Sources As 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

Tropospheric NO2 Columns Retrieved from SCIAMACHY Nov - Apr NO/NO2   w Altitude May - Oct Retrieval Uncertainty ±(5x1014 molec cm-2 + 30%) Tropospheric NO2 (1015 molecules cm-2)

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

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

Simulated Monthly Contribution of Lightning, Soils, and Biomass Burning to NO2 Column Martin et al., 2007

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 Martin et al., 2007 Tropospheric NO2 (1014 molec cm-2)

Annual Mean HNO3 Over 200-350 hPa at Locations & Months with > 60% of HNO3 from Lightning Annual Mean Tropospheric O3 Columns at Locations & Months with > 40% of Column from Lightning Meridional Average Meridional Average GEOS-Chem with Lightning (6±2 Tg N yr-1) GEOS-Chem with Lightning (6±2 Tg N yr-1) ACE-FTS OMI/MLS GEOS-Chem without Lightning GEOS-Chem without Lightning HNO3 Retrieval Error ~35 pptv O3 Retrieval Error < 5 Dobson Units Martin et al., 2007

Sensitivity to decreasing NOx emissions by 1% for each source Lightning NOx Dominant Source for Tropical Tropospheric Ozone Sensitivity to decreasing NOx emissions by 1% for each source DJF 6 Tg N/yr 6 Tg N/yr 6 Tg N/yr MAM JJA SON ΔDU Ozone Production Efficiency from lightning = 3 times that of each surface source Sauvage et al., JGR, 2007

Objectives for Tropospheric NO2 Retrievals Accuracy of 1x1014 molec cm-2 Resolve seasonal variation over northern midlatitudes Challenges for Models Accurate representation of tropospheric NO2 vertical profile NO2 columns / NOx emissions Acknowledgements Supported by NASA and NSERC