Methyl Bromide: Budget and Trends. Shari A. Yvon-Lewis (Texas A&M University)

Transcription

1 Methyl Bromide: Budget and Trends Shari A. Yvon-Lewis (Texas A&M University)

2 Acknowledgements Dr. Eric Saltzman (UCI) Dr. Stephen Montzka (NOAA/GMD) Dr. Jim Butler (NOAA/GMD) Funding: NASA, NSF, and NOAA

3 Methyl Bromide Cycling stratosphere CH 3 Br photolysis rxn with OH Br 100 times more efficient than Cl at destroying Ozone troposphere Br CH 3 Br photolysis; OH Anthropogenic Sources and Natural Terrestrial Sources and Sinks Oceanic Sources and Sinks

4 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

5 2006 Assessment Ozone depleting capacity of the atmosphere has dropped 8-9% since 1992 Montreal Protocol seems to be working 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. From NOAA/GMD

6 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 From NOAA/GMD

7 Atmospheric Methyl Bromide Trends 50 CH 3 Br (ppt) (Past) 1950 Depth (m) Mean gas date (calendar years) 1650 From Saltzman et al. [2004] From Butler et al. [1999]

8 Atmospheric Methyl Bromide Trends (Present) Updated from Montzka et al. [2003]

9 Sources Pre-Phaseout 1996 Ocean 42.0 Fumigation-Quarantine and 12.3 Preshipment 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 (King et al., 2002) (Buffin., 2004) Methyl Bromide Budget (MBTOC, 2006) (Thomas et al., 1997) (van der Werf et al., 1999; Andreae and Merlet, 2001) (Andreae and Merlet, 2001; Yevich and Logan, 2003) (Varner et al., 1999) (Rhew et al., 2000) (Rhew et al., 2001) (Gan et al., 1998) (Lee-Taylor and Holland, 2000) Sinks Ocean -56 OH and hν -77 Soils -41 Plants --- Subtotal Sinks -174 Total (Sources+Sinks) -37 (Yvon-Lewis and Butler, 2002; Saltzman et al., 2004) (Spivakovsky et al., 2000; Prinn et al., 2005) (Shorter et al., 1995; Varner et al., 1999) t= years (Yvon-Lewis et al., modified from Montzka and Fraser et al., 2003 and Clerbaux and Cunnold et al., 2007)

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 CH 3 Br. The lifetime had to be increased above the 0.7yr best estimate in order to fit the data with this model.

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.

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.

13 Model Schematic for this Study NH Ocean NH Soil NH Biom Burn NH Plant/Wet NH unknown SH Ocean SH Soil SH Biom Burn SH Plant/Wet SH unknown Northern Hemisphere Troposphere Interhemispheric Exchange Southern Hemisphere Troposphere NH OH NH hn SH OH SH hn

14 Methyl Bromide Ocean Cycling air sea K W, H A x Invasion p atm x return Evasion K z W, aq Az Uptake aq Emission k k d, Removal biol, aq Az Az aq D z z k z, aq Az Production P 0, Net Sea-to-Air Flux = Evasion - Invasion = Production - Removal = K W (C W /H - p a )

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

16 Oceanic Degradation Rate Constant

17 Production Rate Calculation 100 P f11 0 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:

18 Saturation Anomaly vs. SST Spring/Summer CH 3 Br % Fall/Winter CH 3 Br % BLAST 1 BLAST 2 BLAST 3 GasEx 98 RB ANARE V3 GM98A GM98P G Sea Surface Temperature (ºC) From King et al. [2002]

19 Predicted Saturation Anomalies From King et al. [2002]

20 Oceanic Production Rate Distribution

21 Model Base Year (Monthly Mean NOAA/GMD Data)

22 Seasonality of Known Sources/Sinks During Base Year Northern Hemisphere

23 Seasonality of Missing Source (Yvon-Lewis et al., 2009)

24 Interannual Variability: Biomass Burning (Yvon-Lewis et al., calculated from van der Werf et al., 1999 and Andreae and Merlet, 2001)

25 Interannual Variability: Non-QPS Fumigation (Yvon-Lewis et al., 2009 using Buffin., 2004 and MBTOC, 2006)

26 Interannual Variability: Loss to OH (Yvon-Lewis et al., 2009 using Spivakovsky et al., 2000 and Prinn et al., 2005)

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.

28 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)

29 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)

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 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.

31 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)

32 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 prephaseout seasonality and treated as agricultural. Interannual variability in biomass burning, OH and non-qps anthropogenic emissions included. (Yvon-Lewis et al., 2009)

33 (Yvon-Lewis et al., 2009) Seasonality of Missing Source

34 Missing Source and Lifetime Scenario 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 prephaseout seasonality and treated as natural with no interannual variability. Interannual variability in biomass burning, OH and non-qps anthropogenic emissions included. (Yvon-Lewis et al., 2009)

35 Missing Source and Lifetime 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. (Yvon-Lewis et al., 2009)

36 (Yvon-Lewis et al., 2009) Seasonality of Missing Source

37 Best Estimate (Gg/y) Best Pre-Phaseout Pre-Phaseout Recent (60% Ag) 2007 (60% Ag) Sources Ocean 42.0 *, *, ** Fumigation-Quarantine and Preshipment Fumigation-Soils and Other Gasoline Biomass Burning , , ,6 Biofuel 6.1 6, , ,7 Wetlands Salt marshes Shrublands Rapeseed Fungus Subtotal Sources Sinks Ocean , , OH and hν , , Soils , , Plants Subtotal Sinks Total (Sources+Sinks) -37 *** -31 *** -32 *** 13, 14 14, 15, 16 14, 17 (Yvon-Lewis et al., 2009)

38 Ocean Response to Phaseout (Yvon-Lewis et al., 2009)

39 Atmospheric levels: Decreasing Conclusions 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 years and ODP remains 0.5) Ocean Should be less understurated than before phaseout