Methyl Bromide: Budget and Trends Shari A. Yvon-Lewis (Texas - - PowerPoint PPT Presentation

SLIDE 1

Methyl Bromide: Budget and Trends

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

SLIDE 2

Acknowledgements

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

Funding: NASA, NSF, and NOAA

SLIDE 3

Methyl Bromide Cycling

Anthropogenic Sources and Natural Terrestrial Sources and Sinks

CH3Br

Oceanic Sources and Sinks

photolysis; OH·

stratosphere troposphere

photolysis

CH3Br Br

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

Br

SLIDE 4

♦ 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

SLIDE 5

♦ 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

SLIDE 6

♦ 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

SLIDE 7

Atmospheric Methyl Bromide Trends (Past)

2 4 6 8 10 12 1650 1700 1750 1800 1850 1900 1950 2000 50 60 70 80

CH3Br (ppt) Mean gas date (calendar years)

Depth (m)

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

SLIDE 8

Atmospheric Methyl Bromide Trends (Present)

Updated from Montzka et al. [2003]

SLIDE 9

Pre-Phaseout 1996 Sources Ocean 42.0 Fumigation-Quarantine and Preshipment 12.3 Fumigation-Soils and Other 31.0 Gasoline 5.7 Biomass Burning 11.3 Biofuel 6.1 Wetlands 4.6 Salt marshes 14.6 Shrublands 1 Rapeseed 6.6 Fungus 1.7 Subtotal Sources 137 Sinks Ocean

• 56

OH and hν

• 77

Soils

• 41

Plants

• Subtotal Sinks
• 174

Total (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)

SLIDE 10

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.

SLIDE 11

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.

SLIDE 12

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.

SLIDE 13

NH Soil

Model Schematic for this Study

Northern Hemisphere Troposphere Southern Hemisphere Troposphere

Interhemispheric Exchange

NH Ocean NH OH NH hn SH OH SH hn NH Biom Burn NH Plant/Wet SH Soil SH Ocean SH Biom Burn SH Plant/Wet NH “unknown” SH “unknown”

SLIDE 14

Methyl Bromide Ocean Cycling

Invasion Evasion

return

Uptake Emission Removal Production

air sea

Az z k D

aq z z



 ,

          Az k Az k

aq biol aq d

 

  , ,

Az z K

aq W   ,

 ,

P

atm W

p x H A K

   ,

x aq

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

SLIDE 15

Global Ocean Data

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

SLIDE 16

Oceanic Degradation Rate Constant

SLIDE 17

Production Rate Calculation

 

100 P

f11

z C z D C k k H p z K

z W biol chem a g W

                

 

, 100 Anomaly Saturation     

a a W g

p p H C

Where:

SLIDE 18

Saturation Anomaly vs. SST

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

From King et al. [2002]

• 100
• 50

50 100 150

• 4
• 2

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

• 100
• 50

50 100 150

Spring/Summer CH3Br % Sea Surface Temperature (ºC)

Fall/Winter CH3Br %

SLIDE 19

Predicted Saturation Anomalies

From King et al. [2002]

SLIDE 20

Oceanic Production Rate Distribution

SLIDE 21

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

SLIDE 22

Seasonality of Known Sources/Sinks During Base Year

Northern Hemisphere

SLIDE 23

Seasonality of Missing Source

(Yvon-Lewis et al., 2009)

SLIDE 24

Interannual Variability: Biomass Burning

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

SLIDE 25

Interannual Variability: Non-QPS Fumigation

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

SLIDE 26

Interannual Variability: Loss to OH

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

SLIDE 27

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.

SLIDE 28

Interannual Variability

(Yvon-Lewis et al., 2009)

Scenario 1: Interannual variability in biomass burning only Scenario 2: Interannual variability in OH only. After 2004, no interannual variations are included.

SLIDE 29

Interannual Variability

(Yvon-Lewis et al., 2009)

Scenario 3: Interannual variability in non-QPS anthropogenic emissions

• nly due to phaseout.

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

SLIDE 30

Scenarios Examining Missing Source and Lifetime

5 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

• bserved 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

• bserved 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.

SLIDE 31

Missing Source and Lifetime

(Yvon-Lewis et al., 2009)

Scenario 5: 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.

SLIDE 32

Missing Source and Lifetime

(Yvon-Lewis et al., 2009)

Scenario 6: Missing source reduced by 50%, and atmospheric lifetime

• f 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.

SLIDE 33

Seasonality of Missing Source

(Yvon-Lewis et al., 2009)

SLIDE 34

Missing Source and Lifetime

(Yvon-Lewis et al., 2009)

Scenario 7: Missing source reduced by 50%, and atmospheric lifetime

• f 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.

SLIDE 35

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. Interannual

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

SLIDE 36

Seasonality of Missing Source

(Yvon-Lewis et al., 2009)

SLIDE 37

(Yvon-Lewis et al., 2009)

Best Estimate (Gg/y) Best Pre-Phaseout Pre-Phaseout Recent 1996 1996 (60% Ag)§ 2007 (60% Ag)§ Sources Ocean 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 Sinks Ocean

• 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
• 146

Total (Sources+Sinks)

• 37

***

• 31

***

• 32

***

SLIDE 38

Ocean Response to Phaseout

(Yvon-Lewis et al., 2009)

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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