Methyl Bromide: Budget and Trends

Shari A. Yvon-Lewis(Texas A&M University)

Acknowledgements

Dr. Eric Saltzman (UCI)Dr. Stephen Montzka (NOAA/GMD)Dr. Jim Butler (NOAA/GMD)

Funding: NASA, NSF, and NOAA

Methyl Bromide Cycling

Anthropogenic Sources and Natural Terrestrial Sources and Sinks

CH3Br

Oceanic Sources and Sinks

photolysis; OH·

stratosphere

troposphere

photolysisCH3Br Brrxn with OH·100 times more efficient than Cl at destroying Ozone

Br

♦ 1998 Scientific Assessment of Ozone Depletion» Budget remains out of balance (sinks>sources by 83 Gg/y)» Lifetime is 0.7 y» Ocean is a small net sink» Fumigation could account for 10-40% of all sources

♦ 2002 Scientific Assessment of Ozone Depletion» 20th century atmospheric history obtained from firn» Some new natural sources identified» Budget is still out of balance (sinks>sources by 45 Gg/y), and

lifetime remains 0.7 y with a small net ocean sink» Fumigation release estimates remain at ~41 Gg/y

Methyl Bromide and Ozone Depletion

♦ Ozone depleting capacity of the atmosphere has dropped 8-9%since 1992

♦ Montreal Protocol seems to be working

♦ CH3Br decreased by 14% since 1997 (more than expected)

♦ Budget still out of balance (sinks > sources by 45 Gg/y)

♦ Bromine still a major player with no detectable decrease in the stratosphere, yet.

2006 Assessment

From NOAA/GMD

♦ The Antarctic ozone hole still exists but is not increasing in size

♦ Column ozone remains lower than during the 1960’s -1980

2006 Assessment cont’d

From NOAA/GMD

Atmospheric Methyl Bromide Trends(Past)

0 2 4 6 8 10 12

1650

1700

1750

1800

1850

1900

1950

200050

60

70

80

CH3Br (ppt)

Mean gas date (calendar years)

Dep

th (m

)

From Saltzman et al. [2004] From Butler et al. [1999]

Atmospheric Methyl Bromide Trends(Present)

Updated from Montzka et al. [2003]

Pre-Phaseout1996

SourcesOcean 42.0Fumigation-Quarantine and Preshipment

12.3

Fumigation-Soils and Other 31.0Gasoline 5.7Biomass Burning 11.3Biofuel 6.1Wetlands 4.6Salt marshes 14.6Shrublands 1Rapeseed 6.6Fungus 1.7Subtotal Sources 137

SinksOcean -56OH and hν -77Soils -41Plants ---Subtotal Sinks -174Total (Sources+Sinks) -37

Methyl Bromide Budget

(Yvon-Lewis et al., 2009 - modified from Montzka and Fraser et al., 2003 and Clerbaux and Cunnold et al., 2007)

t= 0.7-0.8 years

(Yvon-Lewis and Butler, 2002; Saltzman et al., 2004)

(Shorter et al., 1995; Varner et al., 1999)

(MBTOC, 2006)

(King et al., 2002)

(van der Werf et al., 1999; Andreae and Merlet, 2001)

(Rhew et al., 2000)(Rhew et al., 2001)(Gan et al., 1998)

(Lee-Taylor and Holland, 2000)

(Buffin., 2004)

(Thomas et al., 1997)

(Andreae and Merlet, 2001; Yevich and Logan, 2003)

(Varner et al., 1999)

(Spivakovsky et al., 2000; Prinn et al., 2005)

Previous Modeling Studies• Pilinis et al. [1996] and Anbar et al. [1996] predicted large

supersaturations in the Southern Ocean.• Lee-Taylor et al. [1998] prescribed the SA as a function of

latitude with no seasonal variation and coupled the ocean to a 3D atmospheric model. Determined that 50 – 70% of missing source is in SH and biased towards tropics.

• Reeves et al. [2003] used the King et al. [2000] SST SA relationship which has one relationship for the whole year. Modeled the firn air data and determined that there must have been a pre-industrial addition source in the SH.

• Montzka et al. [2003] used a box model with varying anthropogenic emission fractions, varying lifetimes, and emissions from soils to fit the observed recent decline in atmospheric CH3Br. The lifetime had to be increased above the 0.7yr best estimate in order to fit the data with this model.

Previous Modeling Studies (cont’d)• Saltzman et al. [2004] combined measurements and modeling to

assess preindustrial concentrations, missing source and budget. Model included an interactive ocean. Preindustrial southern hemisphere mixing ratio is 5.8 ppt. Most of the SH missing source not anthropogenic.

• Warwick et al. [2006] missing source likely tropical and subtropical plants and biomass burning.

This Study• Includes seasonality of sources and sinks• Includes biofuel source• Includes an interactive ocean model• Examines interannual variability in selected sources

and sinks.• Uses extended observations.• Assesses missing source seasonality, interannual

variability, and dependence on lifetime.• Determines oceanic response to phaseout.

NH Soil

Model Schematic for this Study

Northern HemisphereTroposphere

Southern HemisphereTroposphere

InterhemisphericExchange

NH OceanNH OH

NH hn

SH OH

SH hn

NH Biom BurnNH Plant/Wet

SH Soil

SH Ocean

SH Biom BurnSH Plant/Wet

NH “unknown”

SH “unknown”

Methyl Bromide Ocean Cycling

Invasion Evasion

return

Uptake Emission

Removal Production

airsea

AzzkD

aqzz ,

Azk

Azk

aqbiol

aqd

,

,

Azz

Kaq

W ,

,0P

atmW pxH

AK

, x

aq

Net Sea-to-Air Flux = Evasion - Invasion= Production - Removal= KW (CW/H - pa)

Global Ocean Data

BLAST 1, BLAST 2, BLAST 3, GasEx 98, RB-99-06, ANARE V3, GM98A, GM98P, G99

Oceanic Degradation Rate Constant

Production Rate Calculation

100

P f110 z

Cz

DCkkHp

zK z

WbiolchemagW

,100Anomaly Saturation

a

aWg p

pHCWhere:

Saturation Anomaly vs. SST

BLAST 1BLAST 2BLAST 3GasEx 98RB-99-06

ANARE V3GM98AGM98P

G99

From King et al. [2002]

-100

-50

0

50

100

150

-4 -2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32-100

-50

0

50

100

150

Sprin

g/Su

mm

er C

H3B

r %

Sea Surface Temperature (ºC)

Fall/

Win

ter C

H3B

r %

Predicted Saturation Anomalies

From King et al. [2002]

Oceanic Production Rate Distribution

Model Base Year(Monthly Mean 1995-1998 NOAA/GMD Data)

Seasonality of Known Sources/Sinks During Base Year

NorthernHemisphere

Seasonality of Missing Source

(Yvon-Lewis et al., 2009)

Interannual Variability: Biomass Burning

(Yvon-Lewis et al., 2009 - calculated from van der Werf et al., 1999 and Andreae and Merlet, 2001)

Interannual Variability: Non-QPS Fumigation

(Yvon-Lewis et al., 2009 using Buffin., 2004 and MBTOC, 2006)

Interannual Variability: Loss to OH

(Yvon-Lewis et al., 2009 – using Spivakovsky et al., 2000 and Prinn et al., 2005)

Scenarios Examining Interannual Variability

1 Interannual variability in biomass burning only

2 Interannual variability in OH only. After 2004, no interannual variations are included.

3 Interannual variability in non-QPS anthropogenic emissions only due to phaseout.

4 Interannual variability in biomass burning, OH and non-QPS anthropogenic emissions.

Interannual Variability

(Yvon-Lewis et al., 2009)

Scenario 1: Interannualvariability in biomass burning only

Scenario 2: Interannualvariability in OH only. After 2004, no interannualvariations are included.

Interannual Variability

(Yvon-Lewis et al., 2009)

Scenario 3: Interannualvariability in non-QPS anthropogenic emissions only due to phaseout.

Scenario 4: Interannualvariability in biomass burning, OH and non-QPS anthropogenic emissions.

Scenarios Examining Missing Source and Lifetime5 Missing source term treated as agricultural emissions and allowed to

decrease with phaseout. Interannual variability in biomass burning, OH and non-QPS anthropogenic emissions included.

6 Missing source reduced by 50%, and atmospheric lifetime of CH3Br increased to 0.84 yr. Remaining missing source adjusted to match the observed pre-phaseout seasonality and treated as agricultural. Interannual variability in biomass burning, OH and non-QPS anthropogenic emissions included.

7 Missing source reduced by 50%, and atmospheric lifetime of CH3Br increased to 0.84 yr. Remaining missing source adjusted to match the observed pre-phaseout seasonality and treated as natural with no interannual variability. Interannual variability in biomass burning, OH and non-QPS anthropogenic emissions included.

8 Agricultural emissions increased to 60%, and atmospheric lifetime kept as it was in scenarios 1-5. Missing source reduced by the amount of the agricultural increase. Interannual variability in biomass burning, OH and non-QPS anthropogenic emissions included.

Missing Source and Lifetime

(Yvon-Lewis et al., 2009)

Scenario 5: Missing source term treated as agricultural emissions and allowed to decrease with phaseout. Interannualvariability in biomass burning, OH and non-QPS anthropogenic emissions included.

Missing Source and Lifetime

(Yvon-Lewis et al., 2009)

Scenario 6: Missing source reduced by 50%, and atmospheric lifetime of CH3Br increased to 0.84 yr. Remaining missing source adjusted to match the observed pre-phaseout seasonality and treated as agricultural. Interannual variability in biomass burning, OH and non-QPS anthropogenic emissions included.

Seasonality of Missing Source

(Yvon-Lewis et al., 2009)

Missing Source and Lifetime

(Yvon-Lewis et al., 2009)

Scenario 7: Missing source reduced by 50%, and atmospheric lifetime of CH3Br increased to 0.84 yr. Remaining missing source adjusted to match the observed pre-phaseout seasonality and treated as natural with no interannual variability. Interannual variability in biomass burning, OH and non-QPS anthropogenic emissions included.

Missing Source and Lifetime

(Yvon-Lewis et al., 2009)

Scenario 8: Agricultural emissions increased to 60%, and atmospheric lifetime kept as it was in scenarios 1-5. Missing source reduced by the amount of the agricultural increase. Interannualvariability in biomass burning, OH and non-QPS anthropogenic emissions included.

Seasonality of Missing Source

(Yvon-Lewis et al., 2009)

(Yvon-Lewis et al., 2009)

Best Estimate (Gg/y)Best

Pre-Phaseout Pre-Phaseout Recent1996 1996 (60%

Ag)§2007 (60%

Ag)§

SourcesOcean 42.0 *,1 42.0 *,1 42.0 **

Fumigation-Quarantine and Preshipment

12.3 2 12.3 2 13.82 3

Fumigation-Soils and Other 31.0 3 36.6 3 5.2 3

Gasoline 5.7 4 5.7 4 5.7 4

Biomass Burning 11.3 5,6 11.3 5,6 11.3 5,6

Biofuel 6.1 6,7 6.1 6,7 6.1 6,7

Wetlands 4.6 8 4.6 8 4.6 8

Salt marshes 14.6 9 14.6 9 14.6 9

Shrublands 1 10 1 10 1 10

Rapeseed 6.6 11 6.6 11 6.6 5

Fungus 1.7 12 1.7 12 1.7 12

Subtotal Sources 137 143 113

SinksOcean -56 13, 14 -56 13, 14 -48.6 13, 14

OH and hν -77 14, 15 -77 14, 15 -63.6 14, 15, 16

Soils -41 14, 17 -41 14, 17 -34.0 14, 17

Plants --- --- ---Subtotal Sinks -174 -174 -146Total (Sources+Sinks) -37 *** -31 *** -32 ***

Ocean Response to Phaseout

(Yvon-Lewis et al., 2009)

Conclusions• Atmospheric levels:

– Decreasing– Not to preindustrial levels, yet.

• Missing source– Portion is likely anthropogenic (60% emission rather

than 50% emission– Not the result of overestimated sinks (lifetime remains

0.7-0.8 years and ODP remains 0.5)• Ocean

– Should be less understurated than before phaseout