NOx Source Composition Climate Earth System Lightning Chemistry

NOx 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

Overview NOx Source Composition Climate Earth System • Formation of nitrogen oxides (NOx) – 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

How is NO formed? • Heating in lightning channel NOx Source Composition O 2 N 2 Climate Earth System O + O (498 k. J. mol-1) N + N (941 k. J. mol-1) • Plasma formation – High levels of O, N, OH, NO • Rapid cooling preserves NO – NOx 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

Where is NO formed? NOx Source Vertical Distribution Composition • Model-based estimates – – Climate Earth System 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 8 km Pickering et al. , 1998

How much NO is formed? NOx Source Cannot be measured directly; need to estimate using: Composition Climate Earth System Flash extrapolation 5 (0. 6 -13) Tg. N/yr • Base on flash energy, flash length or flash rate • Typical flash: 2 -40× 1025 molecules NO • Global flash rate from OTD: 44 s-1 Storm extrapolation 5 (1 -25) Tg. N/yr • Observational assessment of ΔNO (0. 3 -1. 9 ppbv) • Estimate number of storms (1800 concurrently) • Estimate mean anvil outflow Global Models 5 (2 -8) Tg. N/yr • Base on NOx, O 3 and NOy deposition Best estimate: 5± 3 Tg. N/yr (uncertain!) Detailed summary of methods in Schumann and Huntrieser, ACP, 2007

Global NOx Sources Global NO Emissions Present-day NOx Sources (Tg. N/yr) NOx Source Composition Climate Fossil Fuel 28 Earth System Biomass Fires 10 Soil 5. 5 Lightning Free Troposphere NO Emissions 5 Aircraft 0. 7 Stratosphere 0. 5 Total ~50 Lightning contribution ~10% of current NOx source ~40% of preindustrial source Latitude

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

Source Distribution Annual total NO source NOx Source kg. N/km 2/yr Composition Climate Earth System CTM with ECMWF met flashes/km 2/yr LIS flash frequency

Tropospheric Fate of NO NOx Source Composition Climate Chemical transformation and deposition HO 2 OH RNO 3, N 2 O 5 hydrolysis Earth System NO OH NO 2 HNO 3 Lifetime 10 -20 days Wet and dry deposition R hv PAN O 3 Lifetime 1 -100 days Dry deposition Altitude Dependence Altitude NOx Lifetime O 3 Prod. Eff. 8 -12 km 10 days 50 4 -8 km 5 days 15 0 -4 km 1 day 5

Response to Lightning NOx Source • Impact on Global Tropospheric Chemistry Composition Climate With Lightning Without Lightning Δ due to Lightning 309 262 15% O 3 Production (Tg/yr) 4950 4250 14% O 3 Deposition (Tg/yr) 945 875 7% NOy Deposition (Tg/yr) 50 45 10% CH 4 Lifetime (yr) 8. 7 10. 3 -18% Earth System O 3 Burden (Tg)

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

Effects on NOy Deposition Lightning NO Source NOx Source NOy Deposition January July Composition Climate Earth System kg. N/km 2/month

Effects on Surface O 3 Lightning NO Source NOx Source Surface O 3 January July Composition Climate Earth System kg. N/km 2/month ppbv

Effects on O 3 Deposition Lightning NO Source NOx Source O 3 Deposition January July Composition Climate Earth System kg. N/km 2/month kg/km 2/month

Lightning and Climate NOx Source Composition Climate Earth System • Interactions through greenhouse gas O 3 – Contribution of lightning ~45 -50 Tg O 3 in troposphere – Radiative forcing ~+0. 2 Wm-2 (42 m. W m-2 DU-1, IPCC) – Direct short-term warming from O 3 • Implications: – Positive climate feedback NO • 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) A temperature increase of 2°C may give extra 1. 5 Tg. N/yr: more than increase in air traffic! Climate O 3 External Forcing

Lightning and Climate NOx Source Composition Climate Earth System • 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 m. W m-2 ppb-1 IPCC) Also reduces O 3 RF by ~⅓ • Implications NO – Counteracts O 3 warming – No positive feedback cycle • Net effect of lightning NO CH 4 – Small radiative cooling! Climate O 3

Lightning and Climate Integrated Radiative Forcing from NO Sources NOx Source Composition Climate Fossil Fuel Responses to 0. 5 Tg. N/yr Biomass Earth System Tropics Net Warming Aircraft Net Cooling Lightning Earlier studies with a 10% change of lightning NO show an integrated net cooling (only aircraft NO causes a warming) [Wild et al. , 2001]

Earth System Interactions NOx Source Composition Climate Earth System • Nitrogen fertilization – Wet and dry deposition of NOy – Provides nutrients to vegetation and marine ecosystems • Vegetation damage – O 3 deposition causes leaf damage • Implications – – Ozone damage to potato leaves Crop production Species distributions Uptake of CO 2 VOC emissions Smaller impacts than from fossil fuel usage, but full interactions have not been quantified! UDA-ARS Air Quality Program, NCSU

Earth System Interactions NOx Source Composition Climate Earth System • 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 NOx, CO, VOC, CO 2, aerosols • Direct and indirect effects; albedo changes – Influence on vegetation patterns • Effects on carbon cycling • Sensitivity to climate change

Conclusions NOx Source Composition Climate Earth System • Major environmental impacts – – Important role in tropospheric composition Climate: O 3, CH 4 (net cooling) Vegetation: O 3 and NOy deposition Fire: O 3, NOy, 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. , Met. Office Had. GEM 3, NERC QUEST ESM]