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ATMOS 397GATMOS 397GBiogeochemical Cycles and Global ChangeBiogeochemical Cycles and Global Change

Lecture 14: Methane and COLecture 14: Methane and CO

Don WuebblesDon Wuebbles

Department of Atmospheric SciencesDepartment of Atmospheric Sciences

University of Illinois, Urbana, ILUniversity of Illinois, Urbana, IL

March 6, 2003March 6, 2003

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Tropospheric OH July -- MOZART IITropospheric OH July -- MOZART II

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Tropospheric OH (January) -- MOZART IITropospheric OH (January) -- MOZART II

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OH concentrationsOH concentrations

OH depends non-linearly on atmospheric concentrations of many tropospheric gases

most important gases: CH4, CO, NOx, tropospheric O3, NMHCs

other factors: tropospheric water vapor, uv radiation flux which depends on stratospheric ozone

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Simplified CHSimplified CH44/OH/CO Chemistry/OH/CO Chemistry

CH4

oxidizes to CO OH + CH4

CO OH + CO OH

NMHCs

UV O3 H2O NOx

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SOURCES OF TROPOSPHERIC OZONESOURCES OF TROPOSPHERIC OZONE

?

?

?

Fires BiosphereHumanactivity

Lightning

Oceanphysicschemistrybiology

Nitrogen oxides (NOx)CO, Hydrocarbons

hOzone (O3)

h, H2OHydroxyl (OH)

The Pacman of the atmosphere!

Complex non-linear chemistry

Tropopause(8-18 km)Stratospheric ozone

STRATOSPHERE

TROPOSPHERE

O2 + h

From Daniel Jacob

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Decay of an Impulse EmissionDecay of an Impulse Emission

0

0.2

0.4

0.6

0.8

1

0 50 100 150 200 250 300 350 400 450 500Year

Impulse Response Curves

C2F6

CH4

CO2

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Methane: Lifetime vs. Response TimeMethane: Lifetime vs. Response Time

Atmospheric lifetime of CH4m

= Burden / flux ~ 9 years

— 9.6 years in IPCC (2001)

Response time is the e-folding time after a

perturbation

Response time ~ 1.4 x ~ 13 years

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Trends in Tropospheric OHTrends in Tropospheric OH

Based on Krol et al. (2002)

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Estimated Changes in CH4 Source and Sink

From NOAA CMDL, E. DlugokenckyAssumes fixed lifetime of CH4 = 8.9 years

Mean emission rate of period of observations is 550 Tg CH4 yr-1.

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Earlier Estimates for Trends in Anthropogenic CHEarlier Estimates for Trends in Anthropogenic CH44 EmissionsEmissions

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50

100

150

200

250

300

350

400

1955 1960 1965 1970 1975 1980 1985 1990

Year

CH

4 E

mis

sion

s (T

gCH

4/yr

) Rice Domestic RuminantsBiomass Burning LandfillsAnimal Waste Human WasteCoal Natural Gas & Oil

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Methane Growth Rate

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Methane: Changes in Growth RateMethane: Changes in Growth Rate

1991-1992 After the eruption of Mt. Pinatubo, a large positive anomaly in

growth rate was observed at tropical latitudes. It has been attributed to short-term decreases in solar UV in the tropics immediately following the eruption that decreased OH formation rates in the troposphere (Dlugokencky et al., 1996).

A large decrease in growth was observed, particularly in high northern latitudes, in 1992. This feature has been attributed in part to decreased northern wetland emission rates resulting from anomalously low surface temperatures (Hogan and Harriss, 1994) and in part to stratospheric ozone depletion that increased tropospheric OH (Bekki et al., 1994; Fuglestvedt et al., 1994).

Records of changes in the 13C/12C ratios in atmospheric CH4 during this period suggest the existence of an anomaly in the sources or sinks involving more than one causal factor (Lowe et al., 1997; Mak et al., 2000).

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Methane: Changes in Growth RateMethane: Changes in Growth Rate

1998

High northern and southern tropical latitudes have been

linked to interannual variations in temperature and soil

moisture content in wetland regions, thereby affecting CH4

emissions, and emphasizing the strong link between wetland

CH4 emissions and climate.

Observations suggest that global emissions were greater

than average by 24 Tg CH4

A process based model, which included soil-temperature

and precipitation anomalies, was used to calculate CH4

emission anomalies from wetlands of +24.6 Tg CH4, split

nearly equally between high-northern latitudes and the

southern tropics [Dlugokencky et al., 2001].

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Modeling sources of CHModeling sources of CH44

Prediction of methane emissions from scenarios of basic variables including:

temperature changes population growth evolution of land use patterns future energy demand and sources technological improvements

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2001 IPCC SRES Projected CH2001 IPCC SRES Projected CH44 Emissions Emissions

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Derived Concentrations for MethaneDerived Concentrations for Methane

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Observed

2-D Model

1992

Pre-ind.

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CH4 only

All GHGs

Ratio

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Reductions in CHReductions in CH44, CO and NOx

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1.5

2

2.5

3

Me

tha

ne

Co

nc

en

tra

tio

n,

pp

m

20

00

20

20

20

40

20

60

20

80

21

00

YEAR

MSA750MSA650MSA550MSA450

IS92A

0.5

1

1.5

2

2.5

Me

tha

ne

Co

nc

en

tra

tio

n,

pp

m

20

00

20

20

20

40

20

60

20

80

21

00

YEAR

MSA750MSA650MSA550MSA450

IS92A

Reduce CO and NOxReduce CO and NOx

Reduce CO but not NOxReduce CO but not NOx

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Change in Total Ozone (%) for 2 x [CHChange in Total Ozone (%) for 2 x [CH44]

Δ OΔ O33= +3.4%= +3.4%

University of University of Illinois 2-D Illinois 2-D ModelModel

Month

Latitude

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Change in Local Ozone (%) for 2 x [CHChange in Local Ozone (%) for 2 x [CH44]

University of University of Illinois 2-D Illinois 2-D ModelModel