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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. Formation of nitrogen oxides (NO x ) How, where, how much?

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lightning chemistry and the impacts on climate

Lightning, Chemistry and the Impacts on Climate

Oliver Wild

Department of Environmental Science Lancaster University

Royal Meteorological Society: The Electrifying Atmosphere, 12th Dec 2007

overview
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
how is no formed
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. N

Olivier Staiger

where is no formed
Where is NO formed?

Vertical Distribution

  • 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

how much no is formed
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

global no x sources
Global NOx Sources

Global NO Emissions

Lightning contribution

~10% of current NOx source

~40% of preindustrial source

Free Troposphere NO Emissions

Latitude

source distribution
Source Distribution

Annual total NO source

kgN/km2/yr

  • 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

source distribution8
Source Distribution

Annual total NO source

kgN/km2/yr

CTM with ECMWF met

flashes/km2/yr

LIS flash frequency

tropospheric fate of no
Tropospheric Fate of NO

Chemical transformation and deposition

HO2

OH

RNO3, N2O5

hydrolysis

OH

NO

NO2

HNO3

Lifetime 10-20 days

R

Wet and dry deposition

hv

PAN

O3

Lifetime 1-100 days Dry deposition

Altitude Dependence

response to lightning
Response to Lightning
  • Impact on Global Tropospheric Chemistry
effects of lightning no
Effects of Lightning NO

Lightning NO Source

Change in O3 Chemistry

  • x

15 km

Production

10 km

5 km

Loss

2 km

0 km

Tg/day

Mg/day

Change in CH4 Chemistry

Percent Change in O3 Distribution

Loss

Tg/day

%

effects on no y deposition
Effects on NOy Deposition

Lightning NO Source

NOy Deposition

January

January

July

July

kgN/km2/month

kgN/km2/month

effects on surface o 3
Effects on Surface O3

Lightning NO Source

Surface O3

January

January

July

July

kgN/km2/month

ppbv

effects on o 3 deposition
Effects on O3 Deposition

Lightning NO Source

O3 Deposition

January

January

July

July

kgN/km2/month

kg/km2/month

lightning and climate

NO

Climate

O3

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)

A temperature increase of 2°C may give extra 1.5 TgN/yr: more than increase in air traffic!

External Forcing

lightning and climate16

NO

Climate

O3

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!

CH4

lightning and climate17
Lightning and Climate

Integrated Radiative Forcing from NO Sources

Earlier studies with a 10% change of lightning NO show an integrated net cooling (only aircraft NO causes a warming)

Fossil Fuel

Responses to 0.5 TgN/yr

Biomass

Net Warming

Tropics

Aircraft

Lightning

Net Cooling

[Wild et al., 2001]

earth system interactions
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

Smaller impacts than from fossil fuel usage, but full interactions have not been quantified!

UDA-ARS Air Quality Program, NCSU

earth system interactions19
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
conclusions
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]