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 100 times more photolysis Br CH 3 Br efficient than Cl at rxn with OH · stratosphere destroying Ozone troposphere Br photolysis; OH · CH 3 Br Anthropogenic Sources Oceanic Sources and Sinks and Natural Terrestrial Sources and Sinks
Methyl Bromide and Ozone Depletion ♦ 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 » 20 th 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
2006 Assessment ♦ Ozone depleting capacity of the atmosphere has dropped 8-9% since 1992 ♦ Montreal Protocol seems to be working From NOAA/GMD ♦ CH 3 Br 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 cont’d ♦ The Antarctic ozone hole still exists but is not increasing in size ♦ Column ozone remains lower than during the 1960’s -1980 From NOAA/GMD
Atmospheric Methyl Bromide Trends (Past) CH 3 Br (ppt) 0 2 4 6 8 10 12 50 2000 1950 Mean gas date (calendar years) 60 1900 1850 Depth (m) 70 1800 1750 80 1700 1650 From Saltzman et al . [2004] From Butler et al . [1999]
Atmospheric Methyl Bromide Trends (Present) Updated from Montzka et al . [2003]
Methyl Bromide Pre-Phaseout 1996 Sources Budget Ocean 42.0 ( King et al., 2002) Fumigation-Quarantine and 12.3 ( Buffin. , 2004) Preshipment Fumigation-Soils and Other 31.0 (MBTOC, 2006) Gasoline 5.7 (Thomas et al., 1997) ( van der Werf et al ., 1999; Andreae and Merlet , 2001) Biomass Burning 11.3 Biofuel 6.1 ( Andreae and Merlet , 2001; Yevich and Logan , 2003) Wetlands 4.6 ( Varner et al ., 1999) Salt marshes 14.6 ( Rhew et al ., 2000) Shrublands 1 ( Rhew et al ., 2001) Rapeseed 6.6 (Gan et al., 1998) Fungus 1.7 ( Lee-Taylor and Holland , 2000) Subtotal Sources 137 Sinks Ocean -56 ( Yvon-Lewis and Butler , 2002; Saltzman et al ., 2004) OH and h ν -77 ( Spivakovsky et al. , 2000; Prinn et al ., 2005) Soils -41 ( Shorter et al. , 1995; Varner et al ., 1999) Plants --- Subtotal Sinks -174 t = 0.7-0.8 years Total (Sources+Sinks) -37 (Yvon-Lewis et al. , 2009 - modified from Montzka and Fraser et al., 2003 and Clerbaux and Cunnold et al., 2007)
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 CH 3 Br. 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.
Model Schematic for this Study NH Ocean NH OH NH Soil Northern Hemisphere NH Biom Burn Troposphere NH h n NH Plant/Wet NH “unknown” Interhemispheric Exchange SH Ocean SH OH SH Soil Southern Hemisphere SH Biom Burn Troposphere SH h n SH Plant/Wet SH “unknown”
Methyl Bromide Ocean Cycling Evasion Invasion W K A K W , , x x p Az atm aq H z air sea return aq Emission Uptake Removal Production k Az P d , aq D k 0 , z z , Az aq z k Az biol , aq Net Sea-to-Air Flux = Evasion - Invasion = Production - Removal = K W (C W /H - p a )
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 K p D C g f11 W a z P k k C 0 chem biol W z 100 H z z C H p W a Saturation Anomaly 100 , Where: g p a
Saturation Anomaly vs. SST Spring/Summer CH 3 Br % 150 BLAST 1 100 BLAST 2 50 BLAST 3 0 GasEx 98 -50 RB-99-06 -100 150 Fall/Winter CH 3 Br % ANARE V3 100 GM98A 50 GM98P 0 G99 -50 -100 -4 -2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 Sea Surface Temperature (ºC) From King et al . [2002]
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 Northern Hemisphere
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 Scenario 1: Interannual variability in biomass burning only Scenario 2: Interannual variability in OH only. After 2004, no interannual variations are included. ( Yvon-Lewis et al. , 2009)
Interannual Variability Scenario 3: Interannual variability in non-QPS anthropogenic emissions only due to phaseout. Scenario 4: Interannual variability in biomass burning, OH and non-QPS anthropogenic emissions. ( Yvon-Lewis et al. , 2009)
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 CH 3 Br 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 CH 3 Br 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 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. ( Yvon-Lewis et al. , 2009)
Missing Source and Lifetime Scenario 6: Missing source reduced by 50%, and atmospheric lifetime of CH 3 Br 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. ( Yvon-Lewis et al. , 2009)
Seasonality of Missing Source (Yvon-Lewis et al. , 2009)
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