NO x Source Compositio n 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
Mar 28, 2015
NOx Source
Composition
Climate
Earth System
Lightning, Chemistry and the Impacts on Climate
Oliver WildDepartment of Environmental Science
Lancaster University
Royal Meteorological Society: The Electrifying Atmosphere, 12th Dec 2007
NOx Source
Composition
Climate
Earth System
Overview
• 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
NOx Source
Composition
Climate
Earth System
How is NO formed?
• Heating in lightning channel O2 O + O (498 kJ.mol-1)
N2 N + N (941 kJ.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– O3, N2O, HNO3, H2O2, CO
– Enhancements not observed
• Result: Fixation of atmos. NOlivier Staiger
NOx 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
NOx Source
Composition
Climate
Earth System
How much NO is formed?
Cannot be measured directly; need to estimate using:
Flash extrapolation 5 (0.6-13) TgN/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) TgN/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) TgN/yr• Base on NOx, O3 and NOy deposition
Best estimate: 5±3 TgN/yr (uncertain!)Detailed summary of methods in Schumann and Huntrieser, ACP, 2007
NOx Source
Composition
Climate
Earth System
Global NOx Sources
Lightning contribution~10% of current NOx source
~40% of preindustrial source
Present-day NOx Sources (TgN/yr)
Fossil Fuel 28
Biomass Fires 10
Soil 5.5
Lightning 5
Aircraft 0.7
Stratosphere 0.5
Total ~50
Global NO Emissions
Free Troposphere NO Emissions
Latitude
NOx Source
Composition
Climate
Earth System
Source Distribution
• 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
CTM with ECMWF met
Annual total NO source
kgN/km2/yr
NOx Source
Composition
Climate
Earth System
Source Distribution
CTM with ECMWF met
flashes/km2/yr
LIS flash frequency
Annual total NO source
kgN/km2/yr
NOx Source
Composition
Climate
Earth System
Tropospheric Fate of NO
Chemical transformation and deposition
Altitude NOx Lifetime O3 Prod. Eff.
8-12 km 10 days 50
4-8 km 5 days 15
0-4 km 1 day 5
Altitude Dependence
NO NO2 HNO3
PAN
RNO3, N2O5
Wet and dry deposition
HO2 OH
O3
hv
Lifetime 10-20 days
Lifetime 1-100 days Dry deposition
OH
R
hydrolysis
NOx Source
Composition
Climate
Earth System
Response to Lightning
• Impact on Global Tropospheric Chemistry
With Lightning
Without Lightning
Δ due to Lightning
O3 Burden (Tg) 309 262 15%
O3 Production (Tg/yr) 4950 4250 14%
O3 Deposition (Tg/yr) 945 875 7%
NOy Deposition (Tg/yr) 50 45 10%
CH4 Lifetime (yr) 8.7 10.3 -18%
NOx Source
Composition
Climate
Earth System
Effects of Lightning NO
• x
Change in O3 Chemistry
Change in CH4 Chemistry Percent Change in O3 Distribution
Lightning NO Source
Tg/day
Tg/day
Mg/day
%
15 km
10 km
5 km
2 km
0 km
Production
Loss
Loss
NOx Source
Composition
Climate
Earth System
Effects on NOy DepositionNOy DepositionLightning NO Source
kgN/km2/month kgN/km2/month
January January
July July
NOx Source
Composition
Climate
Earth System
Effects on Surface O3
January
July
Lightning NO Source
kgN/km2/month ppbv
January
July
Surface O3
NOx Source
Composition
Climate
Earth System
Effects on O3 DepositionO3 DepositionLightning NO Source
kgN/km2/month kg/km2/month
January January
July July
NOx Source
Composition
Climate
Earth System
Lightning and Climate
• Interactions through greenhouse gas O3
– Contribution of lightning ~45-50 Tg O3 in troposphere
– Radiative forcing ~+0.2 Wm-2 (42 mW m-2 DU-1, IPCC)
– Direct short-term warming from O3
• Implications:– Positive climate feedback
• Increased O3, warmer climate
• More convection and lightning?
– Sensitivity very uncertain• Lightning source increase?
• Model estimates ~15% K-1
• Δ Humidity reduces P(O3)
NO
O3Climate
External ForcingA temperature increase of 2°C may give extra 1.5 TgN/yr: more than increase in air traffic!
NOx Source
Composition
Climate
Earth System
Lightning and Climate
• Interactions through greenhouse gas CH4
– Equilibrium response: need to consider CH4 changes
– Lifetime drops from 10.3 to 8.7 years (ΔCH4: -500 ppb)
– Radiative forcing ~-0.2 Wm-2 (0.37 mW m-2 ppb-1 IPCC)
– Also reduces O3 RF by ~⅓
• Implications– Counteracts O3 warming
– No positive feedback cycle
• Net effect of lightning NO– Small radiative cooling!
NO
O3Climate
CH4
NOx 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
NOx Source
Composition
Climate
Earth System
Earth System Interactions
• Nitrogen fertilization– Wet and dry deposition of NOy
– Provides nutrients to vegetation and marine ecosystems
• Vegetation damage– O3 deposition causes leaf damage
• Implications– Crop production– Species distributions
– Uptake of CO2
– 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!
NOx 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 NOx, CO, VOC, CO2, aerosols
• Direct and indirect effects; albedo changes
– Influence on vegetation patterns• Effects on carbon cycling
• Sensitivity to climate change
NOx Source
Composition
Climate
Earth System
Conclusions
• Major environmental impacts– Important role in tropospheric composition
– Climate: O3, CH4 (net cooling)
– Vegetation: O3 and NOy deposition
– Fire: O3, 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., MetOffice HadGEM3, NERC QUEST ESM]