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Atmospheric effects of volcanic bromine emissions Taryn M. Lopez UAF Department of Chemistry and Biochemistry.

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Presentation on theme: "Atmospheric effects of volcanic bromine emissions Taryn M. Lopez UAF Department of Chemistry and Biochemistry."— Presentation transcript:

1 Atmospheric effects of volcanic bromine emissions Taryn M. Lopez UAF Department of Chemistry and Biochemistry

2 Importance of volcanic emissions Volcano monitoring Source of trace gases & aerosols to the atmosphere Doukas and McGee, USGS Open File Report, 2007

3 Average Composition of an H 2 O- Rich Magmatic Gas Gerlach, G Cubed, 2004

4 Bromine Halogen elementHalogen element Natural reservoirs: saltwater and the earth’s crust reservoirs: saltwater and the earth’s crust Abundance in Oceans ~67.3 parts per million (ppm by weight) in Oceans ~67.3 parts per million (ppm by weight) Abundance Earth’s crust ~3 ppm (by weight) Earth’s crust ~3 ppm (by weight) Abundance in Atmosphere ~0.5 – 2 parts per trillion (by volume)Abundance in Atmosphere ~0.5 – 2 parts per trillion (by volume) (von Glasow et al, Atmos. Chem. Phys. Discuss., 2004)

5 Annual Global Emissions of HBr (Tg) Cadle, Reviews of Geophysics and Space Physics, 1980

6 First detection of volcanic BrO Soufriere Hills volcano, Montserrat, West IndiesSoufriere Hills volcano, Montserrat, West Indies Bobrowski and others, 2002Bobrowski and others, Bobrowski et al., Nature, 2003

7 Scanning Multiaxis (MAX) DOAS Entrance optics (0.6 deg FOV)Entrance optics (0.6 deg FOV) Quartz optical fibersQuartz optical fibers Ocean Optics USB 2000 UV/Vis spectrometerOcean Optics USB 2000 UV/Vis spectrometer Internal stepper motorInternal stepper motor Temperature stabilized to 10 deg CTemperature stabilized to 10 deg C Bobrowski et al, JGR, 2007

8 Ocean Optics Spectrometer

9 Ocean Optics Spectrometer

10 Ocean Optics Spectrometer

11 Beer-Lambert Law Io = Incident light ε = Molar absorptivity c = Concentration l = Path length -ln(I/I o ) = σNL (Physics) A = -log 10 (I/I o ) = εcl (Chemistry) I = Transmitted light σ = Absorption x-section N = Concentration L = Path length

12 Application of Beer’s Law MAX DOAS Reference Spectrum Sample Spectrum

13 MAX DOAS Reference Spectrum Sample Spectrum

14 Wahner et al., Chem. Phys. Letters, 1988; Weibring, Diploma Thesis, 1986

15 MAX DOAS From Bobrowski et al., Nature, 2003 MAX-DOAS methodology

16 Volcanoes: A significant source of atmospheric BrO! BrO slant column density (SCD) of 2 x molecules/cm 2BrO slant column density (SCD) of 2 x molecules/cm 2 Derived mixing ratio ~ 1 ppbv BrODerived mixing ratio ~ 1 ppbv BrO Estimated emission rate 8.4 x molecules/sEstimated emission rate 8.4 x molecules/s or ~350 t reactive Br/year Global estimate of Br from volcanoesGlobal estimate of Br from volcanoes 14 +/- 6 Tg/year ~ 30,000 t Br/year *Using these estimates and total global Br source flux to the atmosphere of ~60 – 120 molec/cm 3 /s (von Glasow, 2004); volcanic bromine makes up ~ 0.8 – 1.6% of total! (1 molec/cm 3 /s) Bobrowski et al., Nature, 2003

17 BrO Source? Effects?

18 BrO Source? Effects? Redox Chemistry!

19 BrO Source? Effects? Redox Chemistry! Ozone depletion!

20 BrO formation in volcanic plumes Case studies: Mt. Etna volcano, Italy Oppenheimer et al., Geochimica Acta, 2006 & Bobrowski et al., JGR, 2007Case studies: Mt. Etna volcano, Italy Oppenheimer et al., Geochimica Acta, 2006 & Bobrowski et al., JGR, 2007 Collected BrO and SO 2 SCD measurements at 0 km and downwind from sourceCollected BrO and SO 2 SCD measurements at 0 km and downwind from source Oppenheimer et al., Geochimica Acta, 2006 Image Science and Analysis Laboratory, NASA-Johnson Space Center

21 BrO concentrations increase with time Observed an increase in BrO/SO 2 downwind from plume sourceObserved an increase in BrO/SO 2 downwind from plume source –BrO values below detection limit near vent –BrO/SO 2 ~ 4.5 x at 19 km downwind Noticed higher BrO/SO 2 at the edges of plumeNoticed higher BrO/SO 2 at the edges of plume Bobrowski et al., GRL, 2007

22 BrO concentrations increase with time Oppenheimer et al., Geochimica Acta, 2006

23 Where does the BrO come from? HBr found in fluid inclusions in volcanic rocks and in gas condensatesHBr found in fluid inclusions in volcanic rocks and in gas condensates (Bureau et al., EPSL, 2000; Gerlach et al., G Cubed, 2004) HBr is the thermodynamically stable Br species in magma and the atmosphereHBr is the thermodynamically stable Br species in magma and the atmosphere (Oppenheimer et al., Geochimica Acta, 2006)

24 Conversion of HBr to BrO Gas Phase RXN: (1)HBr g + ∙OH g → Br∙ g + H 2 O g k = 1.1 x cm 3 /molecule*s (2)Br∙ g + O 3g  BrO∙ g + O 2 g The value of k, combined with low [OH] makes this sequence too slow to explain BrO observations.The value of k, combined with low [OH] makes this sequence too slow to explain BrO observations. Finlayson Pitts and Pitts, Chemistry of the Upper and Lower Atmosphere, 2000

25 Conversion of HBr to BrO: Heterogeneous reactions (3) ∙g ∙ g  HOBr g + O 2g (3)BrO ∙g +HO 2 ∙ g  HOBr g + O 2g (4)HOBr g  HOBr aq (5)HOBr aq + HBr aq  Br 2aq +H 2 O aq (6)Br 2aq  Br 2g (7)Br 2g + hv  2Br ∙g (8)Br ∙g + O 3g  BrO ∙g + O 2g (9)Net: HO 2 ∙g +O 3g +hv+HBr g  H 2 O aq+ 2O 2g +Br ∙g Reaction requires a surface (sulfate aerosols)!

26 5 m/s plume speed 3340 m 30 m Can field observations be replicated using a chemical model? Bobrowski et al., GRL, D model “MISTRA” (von Glasow, 2002)1D model “MISTRA” (von Glasow, 2002) Air parcel moves across volcanoAir parcel moves across volcano Gas and aerosol chemistry (170 gas phase & 265 aqueous phase rxns)Gas and aerosol chemistry (170 gas phase & 265 aqueous phase rxns) Vertical and horizontal dilutionVertical and horizontal dilution

27 Model input parameters Initial plume: 78% H 2 O, 8.7% CO 2, 2.6% SO 2, 1.3% HCl, 0.006% HBrInitial plume: 78% H 2 O, 8.7% CO 2, 2.6% SO 2, 1.3% HCl, 0.006% HBr Volcanic gas + atmospheric air mixture at thermodynamic equilibriumVolcanic gas + atmospheric air mixture at thermodynamic equilibrium Temperature 600 deg CTemperature 600 deg C Equilibrium composition calculated at 10 s time intervalsEquilibrium composition calculated at 10 s time intervals Bobrowski et al., GRL, 2007

28 BrO forms in volcanic plume Bobrowski et al., GRL, 2007

29 SO 2 : Plume diffusion tracer Bobrowski et al., GRL, 2007 SO 2 concentration in plume decreases gradually as plume diffuses with timeSO 2 concentration in plume decreases gradually as plume diffuses with time BrO/SO 2 plot reflects that BrO is affected by chemical reactions in addition to plume diffusionBrO/SO 2 plot reflects that BrO is affected by chemical reactions in addition to plume diffusion

30 BrO∙Effects? HBr Bromine activation (HBr  Br  BrO)

31 Br Ozone Destruction Cycle BrO HOBr Br Br HO 2 HO 2 O2O2O2O2hv OH O3O3O3O3 O2O2O2O2 Net RXN: O 3 + HO 2 + hv  2O 2 + OH von Glasow et al., Atmos. Chem. Phys. Discuss., 2004

32 Br and HOx Catalytic Cycle BrO HOBr Br Br HO 2 HO 2 O2O2O2O2hv OH O3O3O3O3 O2O2O2O2 CO + O 2 CO 2 Net RXN: CO + O 3  CO 2 + 2O 2 von Glasow et al., Atmos. Chem. Phys. Discuss., 2004

33 Model shows inverse relationship between Ozone and BrO Bobrowski et al., GRL, minutes following model initiation, O 3 levels drop to near zero 20 minutes following model initiation, O 3 levels drop to near zero At this time BrO levels begin to sharply increase At this time BrO levels begin to sharply increase After 90 minutes O 3 levels begin to increase as plume mixes with ambient air After 90 minutes O 3 levels begin to increase as plume mixes with ambient air

34 Use chemical transport model MATCH-MPIC to test theory 3D chemical transport model (MATCH-MPIC) to test impacts of BrO on O 3 in the troposphere3D chemical transport model (MATCH-MPIC) to test impacts of BrO on O 3 in the troposphere Included comprehensive gas phase chemistry and HBr heterogeneous rxnsIncluded comprehensive gas phase chemistry and HBr heterogeneous rxns Global Br source of molec*cm -3 *s -1Global Br source of molec*cm -3 *s -1 4 scenarios different latitude and compositions4 scenarios different latitude and compositions vonGlasow et al., Atmos. Chem. Phys. Discuss., 2004 von Glasow et al., Atmos. Chem. Phys. Discuss., 2004

35 BrO depletes O 3 according to model results BrO mixing ratios of < 2 pptv can result in:BrO mixing ratios of < 2 pptv can result in: – 18% reduction in mean tropospheric O 3 mixing ratios (large areas) –40% reduction in mean tropospheric O 3 mixing ratios (localized areas) vonGlasow et al., Atmos. Chem. Phys. Discuss., 2004 von Glasow et al., Atmos. Chem. Phys. Discuss., 2004

36 Do reactive halogens cause localized ozone holes near volcanoes? Case study: Sakurajima Volcano BrO, ClO, and SO 2 SCD were measured downwind of Sakurajima volcanoBrO, ClO, and SO 2 SCD were measured downwind of Sakurajima volcano Direct SO 2 and O 3 also measured at ObservatoryDirect SO 2 and O 3 also measured at Observatory Strong correlation between BrO, ClO, and SO 2 speciesStrong correlation between BrO, ClO, and SO 2 species Lee et al., GRL, 2005

37 Increase in SO 2 corresponds with decrease in O 3 Lee et al., GRL, 2005

38 HBr Bromine activation (HBr  Br  BrO) BrO Ozone depletion (O 3 + HO 2 + hv  2O 2 + OH)

39 Do large volcanic eruptions cause global stratospheric ozone depletion due to Br chemistry?

40 Kasatochi Volcanic Eruption August 2008 August 2008 –Injected 1.5 Mt SO 2 into atmosphere (Pinatubo  20 Mt) –Plume to 40,000 feet elevation (stratosphere for Kasatochi’s latitude) –SO 2 cloud circled globe in 21 days –Using BrO/SO 2 ratio of ~ (Bobrowski et al., 2007)  150 t BrO injected into atmosphere Alaska Volcano Observatory, Internal Logs, August 2008; Photo by Chris Waythomas

41 Kasatochi SO 2 Cloud Circles Globe Image by Simon Carn, NASA JCET

42 Conclusions Volcanic bromine emissions account for a significant amount of total atmospheric BrVolcanic bromine emissions account for a significant amount of total atmospheric Br Volcanically emitted HBr can produce BrOVolcanically emitted HBr can produce BrO via heterogeneous reactions on sulfate aerosols BrO can catalytically react in an O 3 destruction cycleBrO can catalytically react in an O 3 destruction cycle BrO in volcanic plumes may cause localized ozone holesBrO in volcanic plumes may cause localized ozone holes Future Work Could large volcanic eruptions significantly deplete stratospheric ozone due to BrO chemistry?

43 Thank you for your attention! Questions?


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