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
Global Lightning NOx Source Remains Uncertain�Constrain with Top-down Satellite Observations
SCIAMACHY
Tropospheric NO2 Columns
ACE-FTS
Limb HNO3 Measurements in the Upper Troposphere
OMI & MLS
Both instruments onboard Aura satellite
Tropospheric O3
Current Estimate of Annual Global NOx Sources�As Used In GEOS-Chem
1010 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
Tropospheric NO2 Columns Retrieved from SCIAMACHY
Retrieval Uncertainty
±(5x1014 molec cm-2 + 30%)
Tropospheric NO2 (1015 molecules cm-2)
Nov - Apr
May - Oct
NO/NO2 ↑ ↑
w Altitude
Data from Martin et al., 2006
Simplified Chemistry of Nitrogen Oxides�Exploit Longer Lifetimes in Upper Troposphere �
NO
NO2
NOx lifetime < day
Nitrogen Oxides (NOx)
Boundary
Layer
NO/NO2 ↑ ↑
with altitude
hv
NO
NO2
O3, RO2
hv
HNO3
NOx lifetime ~ week
lifetime ~ weeks
Ozone (O3)
lifetime ~ month
Upper Troposphere
Ozone (O3)
lifetime ~ days
HNO3
O3, RO2
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
Annual Mean NO2 Column at Locations & Months with >60% from Lightning, <25% from Surface Sources
Tropospheric NO2 (1014 molec cm-2)
Meridional Average
SCIAMACHY (Uses 15% of Tropical Observations)
GEOS-Chem with Lightning (8% bias, r=0.75)
GEOS-Chem without Lightning (-60% bias)
NO2 Retrieval Error ~ 5x1014 molec cm-2
GEOS-Chem with Lightning (6±2 Tg N yr-1)
SCIAMACHY
GEOS-Chem without Lightning
ACE HNO3 over 200-350 hPa for Feb 2004 – Feb 2006
HNO3 Mixing Ratio (pptv)
Data from Boone et al., 2005
GEOS-Chem Calculation of Contribution of Lightning to HNO3
HNO3 from Lightning
Fraction from Lightning
Focus on 200-350 hPa
HNO3 With Lightning (6±2 Tg N yr-1)
No Lightning
Fraction of HNO3 from Lightning
Jan
Jul
Annual Mean HNO3 Over 200-350 hPa at Locations & Months with > 60% of HNO3 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)
HNO3 Mixing Ratio (pptv)
ACE-FTS
GEOS-Chem with Lightning (6±2 Tg N yr-1)
GEOS-Chem without Lightning
HNO3 Retrieval Error ~35 pptv
OMI/MLS Tropospheric Ozone Column
Jan
Jul
Data from Ziemke et al. (2006)
Calculated Monthly Contribution of Lightning to O3 Column
O3 Column from Lightning
Column Fraction from Lightning
Annual Mean Tropospheric O3 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 O3 (Dobson Units)
OMI/MLS
GEOS-Chem with Lightning (6±2 Tg N yr-1)
GEOS-Chem without Lightning
O3 Retrieval Error < 5 Dobson Units
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. NO2)
- more observations (e.g. HNO3)
- model development to better represent processes (e.g. lightning NOx representation, vertical transport)
Acknowledgements
Supported by NASA’s Radiation Science Program