1. 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

2. 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)

3. 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)

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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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 % 9% 3%
1.6 Tg N yr % 5% 3%
Martin et al., JGR, 2006

15. 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

16. 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

17. 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

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

19. Simplified Chemistry of Nitrogen Oxides Exploit Longer Lifetimes in Upper Tropospherehv 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)

20. 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

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

22. 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)

23. 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

24. 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

25. 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