1. NO x Source Composition Climate Earth System Lightning, Chemistry and the Impacts on Climate Oliver Wild Department of Environmental Science Lancaster University Royal Meteorological Society: The Electrifying Atmosphere, 12 th Dec 2007

2. NO x Source Composition Climate Earth System Overview Formation of nitrogen oxides (NO x ) –How, where, how much? Effects on atmospheric composition –Oxidation, lifetimes, deposition Implications for climate –Greenhouse gas abundance Implications for the Earth System –Role in global change

3. NO x Source Composition Climate Earth System How is NO formed? Heating in lightning channel O 2 O + O ( 498 kJ.mol -1 ) N 2 N + N ( 941 kJ.mol -1 ) Plasma formation –High levels of O, N, OH, NO Rapid cooling preserves NO –NO x observed in outflow –Also in lab (Cavendish, 1785) Minor products –O 3, N 2 O, HNO 3, H 2 O 2, CO –Enhancements not observed Result: Fixation of atmos. N Olivier Staiger

4. NO x Source Composition Climate Earth System Where is NO formed? Model-based estimates –Atmospheric observations –Cloud-resolving model –Estimate flash rate, yield –Convective redistribution Features –Detrainment in anvils Clearly observed –Downdrafts to surface Assumed, not observed –About 65% above 8km Pickering et al., 1998 Vertical Distribution

5. NO x Source Composition Climate Earth System How much NO is formed? Cannot be measured directly; need to estimate using: Flash extrapolation5 (0.6-13) TgN/yr Base on flash energy, flash length or flash rate Typical flash: 2-40×10 25 molecules NO Global flash rate from OTD: 44 s -1 Storm extrapolation5 (1-25) TgN/yr Observational assessment of ΔNO (0.3-1.9 ppbv) Estimate number of storms (1800 concurrently) Estimate mean anvil outflow Global Models5 (2-8) TgN/yr Base on NO x, O 3 and NO y deposition Best estimate: 5±3 TgN/yr (uncertain!) Detailed summary of methods in Schumann and Huntrieser, ACP, 2007

6. NO x Source Composition Climate Earth System Global NO x Sources Lightning contribution ~10% of current NO x source ~40% of preindustrial source Present-day NO x Sources (TgN/yr) Fossil Fuel 28 Biomass Fires 10 Soil5.5 Lightning 5 Aircraft0.7 Stratosphere0.5 Total~50 Global NO Emissions Free Troposphere NO Emissions Latitude

7. NO x Source Composition Climate Earth System Source Distribution Distribute based on lightning occurrence –Flash observationsreal distribution –Cloud top height –Convective mass fluxderived distribution –Convective precipitation Results shown here use FRSGC/UCI Chemical Transport Model (CTM) with ECMWF met data and convective updraft mass flux CTM with ECMWF met Annual total NO source kgN/km 2 /yr

8. NO x Source Composition Climate Earth System Source Distribution CTM with ECMWF met flashes/km 2 /yr LIS flash frequency Annual total NO source kgN/km 2 /yr

9. NO x Source Composition Climate Earth System Tropospheric Fate of NO Chemical transformation and deposition AltitudeNO x LifetimeO 3 Prod. Eff. 8-12 km10 days50 4-8 km 5 days15 0-4 km1 day 5 Altitude Dependence NONO 2 HNO 3 PAN RNO 3, N 2 O 5 Wet and dry deposition HO 2 OH O3O3 hv Lifetime 10-20 days Lifetime 1-100 days Dry deposition OH R hydrolysis

10. NO x Source Composition Climate Earth System Response to Lightning Impact on Global Tropospheric Chemistry With Lightning Without Lightning Δ due to Lightning O 3 Burden (Tg) 309 26215% O 3 Production (Tg/yr)4950425014% O 3 Deposition (Tg/yr) 945 875 7% NO y Deposition (Tg/yr) 50 4510% CH 4 Lifetime (yr) 8.710.3-18%

11. NO x Source Composition Climate Earth System Effects of Lightning NO x Change in O 3 Chemistry Change in CH 4 ChemistryPercent Change in O 3 Distribution Lightning NO Source Tg/day Mg/day % 15 km 10 km 5 km 2 km 0 km Production Loss

12. NO x Source Composition Climate Earth System Effects on NO y Deposition NO y DepositionLightning NO Source kgN/km 2 /month January July

13. NO x Source Composition Climate Earth System Effects on Surface O 3 January July Lightning NO Source kgN/km 2 /monthppbv January July Surface O 3

14. NO x Source Composition Climate Earth System Effects on O 3 Deposition O 3 DepositionLightning NO Source kgN/km 2 /monthkg/km 2 /month January July

15. NO x Source Composition Climate Earth System Lightning and Climate Interactions through greenhouse gas O 3 –Contribution of lightning ~45-50 Tg O 3 in troposphere –Radiative forcing ~+0.2 Wm -2 (42 mW m -2 DU -1, IPCC) –Direct short-term warming from O 3 Implications: –Positive climate feedback Increased O 3, warmer climate More convection and lightning? –Sensitivity very uncertain Lightning source increase? Model estimates ~15% K -1 Δ Humidity reduces P(O 3 ) NO O3O3 Climate External Forcing A temperature increase of 2°C may give extra 1.5 TgN/yr: more than increase in air traffic!

16. NO x Source Composition Climate Earth System Lightning and Climate Interactions through greenhouse gas CH 4 –Equilibrium response: need to consider CH 4 changes –Lifetime drops from 10.3 to 8.7 years (ΔCH 4 : -500 ppb) –Radiative forcing ~-0.2 Wm -2 (0.37 mW m -2 ppb -1 IPCC) –Also reduces O 3 RF by ~ Implications –Counteracts O 3 warming –No positive feedback cycle Net effect of lightning NO –Small radiative cooling! NO O3O3 Climate CH 4

17. NO x Source Composition Climate Earth System Lightning and Climate Earlier studies with a 10% change of lightning NO show an integrated net cooling (only aircraft NO causes a warming) Integrated Radiative Forcing from NO Sources Lightning Aircraft Tropics Biomass Fossil Fuel Net Cooling Net Warming [Wild et al., 2001] Responses to 0.5 TgN/yr

18. NO x Source Composition Climate Earth System Earth System Interactions Nitrogen fertilization –Wet and dry deposition of NO y –Provides nutrients to vegetation and marine ecosystems Vegetation damage –O 3 deposition causes leaf damage Implications –Crop production –Species distributions –Uptake of CO 2 –VOC emissions Ozone damage to potato leaves UDA-ARS Air Quality Program, NCSU Smaller impacts than from fossil fuel usage, but full interactions have not been quantified!

19. NO x Source Composition Climate Earth System Earth System Interactions Lightning ignition of wildfires –Small effect in tropics due to moist conditions –Accounts for 10-50% of fires over N. America Typically more than half of area burned Implications –Potential feedbacks on climate Emissions of NO x, CO, VOC, CO 2, aerosols Direct and indirect effects; albedo changes –Influence on vegetation patterns Effects on carbon cycling Sensitivity to climate change

20. NO x Source Composition Climate Earth System Conclusions Major environmental impacts –Important role in tropospheric composition –Climate: O 3, CH 4 (net cooling) –Vegetation: O 3 and NO y deposition –Fire: O 3, NO y, aerosol, vegetation damage Big challenges remain –Improved quantification of NO emissions Uncertainties in magnitude, location, response Better integration of observations and models –Quantification of environmental impacts Role of lightning in global change Requires new generation of Earth System Models [e.g., MetOffice HadGEM3, NERC QUEST ESM]