Atmospheric effects of volcanic bromine emissions

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

2. www.usgs.gov Importance of volcanic emissions Source of trace gases & aerosols to the atmosphere Volcano monitoring www.wikipedia.com/ Doukas and McGee, USGS Open File Report, 2007

3. Average Composition of an H2O-Rich Magmatic Gas Gerlach, G Cubed, 2004

4. Bromine • Halogen element • Natural reservoirs: saltwater and the earth’s crust http://minerals.usgs.gov/minerals/pubs/commodity/bromine/) • Abundance in Oceans ~67.3 parts per million (ppm by weight)www.eoearth.org • Abundance Earth’s crust ~3 ppm (by weight) http://en.wikipedia.org/wiki/Abundance_of_elements_in_Earth's_crust • Abundance in Atmosphere ~0.5 – 2 parts per trillion (by volume) • (von Glasow et al, Atmos. Chem. Phys. Discuss., 2004) www.periodictable.com

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 Indies • Bobrowski and others, 2002 www.mvo.ms Bobrowski et al., Nature, 2003

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

8. Ocean Optics Spectrometer www.oceanoptics.com

9. Ocean Optics Spectrometer www.oceanoptics.com

10. Ocean Optics Spectrometer www.oceanoptics.com

11. Beer-Lambert Law A = -log10 (I/Io) = εcl(Chemistry) -ln(I/Io) = σNL (Physics) Io = Incident light ε = Molar absorptivity c = Concentration l = Path length I = Transmitted light σ = Absorption x-section N = Concentration L = Path length

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

13. Reference Spectrum Sample Spectrum Reference Spectrum MAX DOAS

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

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

16. Volcanoes: A significant source of atmospheric BrO! • BrO slant column density (SCD) of 2 x 1015 molecules/cm2 • Derived mixing ratio ~ 1 ppbv BrO • Estimated emission rate 8.4 x 1022 molecules/s or ~350 t reactive Br/year • Global 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/cm3/s (von Glasow, 2004); volcanic bromine makes up ~ 0.8 – 1.6% of total! (1 molec/cm3/s) Bobrowski et al., Nature, 2003

17. Effects? BrO• Source?

18. Effects? BrO• Redox Chemistry! Source?

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

20. BrO formation in volcanic plumes • Case studies: Mt. Etna volcano, Italy Oppenheimer et al., Geochimica Acta, 2006 & Bobrowski et al., JGR, 2007 • Collected BrO and SO2 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/SO2 downwind from plume source • BrO values below detection limit near vent • BrO/SO2 ~ 4.5 x 10-4 at 19 km downwind • Noticed higher BrO/SO2 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 condensates (Bureau et al., EPSL, 2000; Gerlach et al., G Cubed, 2004) • HBr 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) HBrg + ∙OHg→ Br∙g + H2Og k = 1.1 x 10-11 cm3/molecule*s • Br∙g + O3g BrO∙g + O2 g • 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) BrO∙g +HO2∙g HOBrg + O2g (4) HOBrg  HOBraq (5) HOBraq + HBraq  Br2aq +H2Oaq (6) Br2aq  Br2g (7) Br2g+ hv  2Br∙g (8) Br∙g + O3g BrO∙g + O2g • Net: HO2∙g+O3g+hv+HBrgH2Oaq+2O2g+Br∙g Reaction requires a surface (sulfate aerosols)!

26. Can field observations be replicated using a chemical model? 5 m/s plume speed • 1D model “MISTRA” (von Glasow, 2002) • Air parcel moves across volcano • Gas and aerosol chemistry (170 gas phase & 265 aqueous phase rxns) • Vertical and horizontal dilution 30 m 3340 m Bobrowski et al., GRL, 2007

27. Model input parameters • Initial plume: 78% H2O, 8.7% CO2, 2.6% SO2, 1.3% HCl, 0.006% HBr • Volcanic gas + atmospheric air mixture at thermodynamic equilibrium • Temperature 600 deg C • Equilibrium composition calculated at 10 s time intervals Bobrowski et al., GRL, 2007

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

29. SO2: Plume diffusion tracer • SO2 concentration in plume decreases gradually as plume diffuses with time • BrO/SO2 plot reflects that BrO is affected by chemical reactions in addition to plume diffusion Bobrowski et al., GRL, 2007

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

31. O3 O2 Br • BrO• HO2• •OH hv HOBr O2 Br Ozone Destruction Cycle Net RXN: O3 + HO2 + hv  2O2 + OH von Glasow et al., Atmos. Chem. Phys. Discuss., 2004

32. CO + O2 CO2 O3 O2 Br • BrO• HO2• •OH hv HOBr O2 Br and HOx Catalytic Cycle Net RXN: CO + O3 CO2 + 2O2 von Glasow et al., Atmos. Chem. Phys. Discuss., 2004

33. Model shows inverse relationship between Ozone and BrO • 20 minutes following model initiation, O3 levels drop to near zero • At this time BrO levels begin to sharply increase • After 90 minutes O3 levels begin to increase as plume mixes with ambient air Bobrowski et al., GRL, 2007

34. Use chemical transport model MATCH-MPIC to test theory • 3D chemical transport model (MATCH-MPIC) to test impacts of BrO on O3 in the troposphere • Included comprehensive gas phase chemistry and HBr heterogeneous rxns • Global Br source of 60 - 120 molec*cm-3*s-1 • 4 scenarios different latitude and compositions vonGlasow et al., Atmos. Chem. Phys. Discuss., 2004

35. BrO depletes O3according to model results • BrO mixing ratios of < 2 pptv can result in: • 18% reduction in mean tropospheric O3 mixing ratios (large areas) • 40% reduction in mean tropospheric O3 mixing ratios (localized areas) vonGlasow et al., Atmos. Chem. Phys. Discuss., 2004

36. Do reactive halogens cause localized ozone holes near volcanoes?Case study: Sakurajima Volcano • BrO, ClO, and SO2 SCD were measured downwind of Sakurajima volcano • Direct SO2 and O3 also measured at Observatory • Strong correlation between BrO, ClO, and SO2 species http://landsat.usgs.gov/gallery/ Lee et al., GRL, 2005

37. Increase in SO2 corresponds with decrease in O3 Lee et al., GRL, 2005

38. Bromine activation (HBr  Br  BrO) Ozone depletion (O3 + HO2 + hv  2O2 + OH) BrO• HBr

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

40. Kasatochi Volcanic Eruption August 2008 • Injected 1.5 Mt SO2 into atmosphere (Pinatubo  20 Mt) • Plume to 40,000 feet elevation (stratosphere for Kasatochi’s latitude) • SO2 cloud circled globe in 21 days • Using BrO/SO2 ratio of ~ 10-4 (Bobrowski et al., 2007)  150 t BrO injected into atmosphere Alaska Volcano Observatory, Internal Logs, August 2008; Photo by Chris Waythomas

41. Kasatochi SO2 CloudCircles Globe Image by Simon Carn, NASA JCET

42. Conclusions • Volcanic bromine emissions account for a significant amount of total atmospheric Br • Volcanically emitted HBr can produce BrO via heterogeneous reactions on sulfate aerosols • BrO can catalytically react in an O3 destruction cycle • BrO 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?