lightning and atmospheric chemistry - taucolin/courses/atmoselec/nox.pdf · • 1785 cavendish...

• 1785 Cavendish performed the first experiments with a

spark discharge in glass tube. Discovered that oxidized

nitrogen (NOx=NO + NO2) compounds resulted from

the “burning” of air.

•1827 von Liebig discovered nitric acid (HNO3) in rain water and

related it to Cavendish’s experiments. NOx oxidized in drops.

• Nitric acid (HNO3) provides an important source of nitrate for

biosphere. Important in evolution of life.

•1970 Crutzen showed that tropospheric ozone (O3) was strongly

influenced by the amounts of atmospheric NOx.

•Ozone is poisonous to people, animals, plants, and is harmful to

perishable materials such as rubber, plastics, etc.

•1990’s led to a dramatic increase in the study of lightning

produced NOx since O3 is a strong greenhouse gas.

Lightning and Atmospheric Chemistry

OXIDATION STATES OF NITROGEN N has 5 electrons in valence shell a9 oxidation states from –3 to +5

-3 0 +1 +2 +3 +4 +5

NH3

Ammonia

NH4+

Ammonium

R1N(R2)R3

Organic N

N2 N2O

Nitrous

oxide

NO

Nitric

oxide

HONO

Nitrous acid

NO2-

Nitrite

NO2

Nitrogen

dioxide

HNO3

Nitric acid

NO3-

Nitrate

N2O5

Nitrogen

pentoxide

Decreasing oxidation number (reduction reactions)

Increasing oxidation number (oxidation reactions)

Nitrogen: Nitrogen is a major component of the atmosphere, but an essential nutrient in short

supply to living organisms.

free radical free radical

•is the third most important greenhouse

gas

•impacts the Earth’s radiation budget and

can cause changes in atmospheric

circulation patterns.

•is toxic to humans, plants and animals.

TROPOSPHERIC OZONE:

NOx [NO+NO2]:

•is a primary pollutant found in photochemical smog

•is a precursor for tropospheric ozone formation

Why is NOx important?

NOx indirectly affects our local air quality and global

climate Has a strong influence on Ozone (O3) and hydroxyl

radical (OH) concentration

EULINOX

Observational Evidence of LNOx

New Mexico Colorado

(Germany)

Tg N / yr Theoretical estimates

4 Tuck (1976)

18-41 Chameides et al. (1977)

47-100 Chameides (1979)

3 Dawson (1980)

0.9 Hill et al. (1980)

1.2 Bhetanabhotla et al. (1985)

Laboratory estimates

35-47 Chameides et al. (1977)

1.8 Levine et al. (1981)

9.4 Peyrous and Lapeyre (1982)

2.6 Borucki and Chameides (1984)

2.5-8.3 Wang et al. (1998)

Field Measurements

37 Noxon (1976, 1978)

2-4 Kowalczyk and Bauer (1982)

30 Drapcho et al. (1983)

220 Franzblau and Popp (1989)

3 Huntrieser (1999)

Lightning-Produced NOx

Lightning: An Important Source of NOx

~50 Total

0.1-1 (0.4) N2O Degradation

0.7-1 (0.7) Aviation

1-16 (5.5) Soil Emissions

1-20 (5-7) Lightning

4-24 (10) Biomass Burning

28-32 (28) Fossil Fuel Burning

Tg N/yr Current Annual NOx Source

[Schumann and Huntrieser 2007]

Why such large uncertainties?

To get a global number one has to answer 3 questions:

• What is the energy of a “typical” lightning discharge?

• How much NOx is produced per unit energy?

• How do we extrapolate to the globe?

1. Energy of a lightning discharge

E1 = L ------------------ dt I(t)2

(t) r(t)2

E2 = V I(t) dt = V Q

Wang et al. (1998)

How long is a “typical”

lightning channel?

0 100

5 103

10 103

15 103

20 103

25 103

30 103

35 103

40 103

I(t) = Io [exp

-at-exp

-bt+exp

-ct]

Cu

rren

t (A

mp

eres

)

Time (microseconds)

0 20 40 60 80 100

Io = 35 kA

Io = 10-60 kA

V ~ 3x108 Volts

E = 109 – 1010 Joules

<E> = 6.7 x 109 J

(Price et al., 1997)

E2 = V I(t) dt = V Q

2. How much NOx is produced per unit energy?

O2

N2

T~30,000 K

O

O

N

N

NO

NO2

NO

NO

NO

NO

NO2

~1mm ~5 cm

Temperature of Lightning

How much air

is processed by

lightning?

Size of lightning channel

Zel’dovich Reactions

O2 O + O

O + N2 NO + N

N + O2 NO + O

When the lightning channel cools below T ~ 2500 K

NOx remains “fixed” or “frozen” in the atmosphere

(fixed nitrogen)

~85% of NOx is in form of NO

With volume mixing ratios of 1-4%

P (NO) = 1017 molecules/Joule

Wang et al. (1998)

~cm

~ meters

Region of coronae and

streamers due to high electric

fields surrounding channel

Hot channel

O+ + N2 NO+ + N

NO+ + e- NO

NO+ + N N2O+

N2O+ + e- N2O

Much larger volume of air

3. Global Extrapolation

Flashrate Parameterization

Z_IC

Z_CG

CTH

CC

Flashrate parameterization of

Price and Rind [1992]

Fcontinental CTH4.9

Fmarine CTH1.73

IC/CG Ratio parameterization

of Price and Rind [1993]

IC-CG Ratio CC4.0

0C

Using ISCCP

clouds from

1983-1990

Annual mean

NOx production

is 12 Tg N/yr

Price et al. (1997)

Using Satellite Observations of Clouds

0

0.5

1

1.5

Global estimates of monthly NO production (Tg)

Mon

thly

NO

x p

rod

uct

ion

(T

g)

Month

J F M A M J J A S O N D

Using Modelled Clouds

GCM simulations using lightning parameterizations

Total Lightning:

F ~ H5 over land

F ~ H 1.7 over oceans

(Price & Rind, 1992)

Fraction of CG vs. IC lightning:

IC/CG ~ cold cloud thickness

(Price and Rind, 1993)

How do we model lightning in GCMs?

Observations Model

Levy et al.

(1999)

TOP-DOWN ESTIMATES OF GLOBAL LIGHTNING

NOx EMISSIONS

[Martin et al., 2007]

Using SCIAMACHY (NO2), OMI (O3), ACE-FTS (HNO3):

Target locations/times where NO2 column is dominated by

lightning source

Global source of 6 ± 2 TgN/yr from lightning

Obs (satellite)

Model (6 TgN/yr)

Model (4-8 TgN/yr)

Model (no lightning)

Formation of Ozone (O3)

OH + CO H + CO2

H + O2 + M HO2 + M

Low NOx High NOx

HO2 + O3 OH + 2O2

Net: CO + O3 CO2 + 2O2

Ozone destruction

HO2 + NO OH + NO2

NO2 + h NO + O

O + O2 + M O3 + M

Net: CO + 2O2 CO2 + O3

Ozone production

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

July 21, 1998

12UT at 400mb

Maximum NOx production of 1 ppb

Total NOx Lightning NOx

(Flatoy and Hov, 1997)

Ozone production : max of 1 ppb/hour

July 21, 1998 9-12UT

Total Ozone

Production

Ozone Production

Due to Lightning

NOx from lightning Ozone from lightning

July 1998 mean at 400mb

NASA Goddard Institute for Space Studies (GISS)

General Circulation Model (GCM)

2xCO2 climate - Control = ~ 4o C global warming

+30%

Price & Rind

(1994)

CHANGING LNOX?

Warmer climate = more thunderclouds = more lightning

Impact:

(1) increasing UT ozone formation (positive forcing)

(2) Increasing OH leads to small reductions in CH4

(negative forcing)

Models predict

+ 4-60 % LNOx

per °K

Summary and Conclusions

•Lightning is a major source of NOx in the troposphere

and is likely the largest source in the upper troposphere.

•Lightning produces between 5-10 Tg N/yr.

•While NOx production by lightning is a minor contributor

to surface O3 concentrations, and is likely the largest

contributor in the tropical upper troposphere.

•75% of the lightning-NOx and O3 is produced in the tropics

•The highest global production of LNOx occurs during JJA and the

lowest production occurs during DJF.

•Due to this natural imbalance, the northern hemisphere had a

natural bias in tropospheric ozone, even in pre-industrial times.

•Future climate change may increase global lightning activity

resulting in an increase in tropospheric O3 (positive feedback).