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The impact of volcanic aerosols on stratospheric chemistry with implications for geoengineering

The impact of volcanic aerosols on stratospheric chemistry with implications for geoengineering. Simone Tilmes (tilmes@ucar.edu) WACCM team, Doug Kinnison, Rolando Garcia, Anne Smith, Ryan Neely, Andrew Conley, Jean-Francois Lamarque

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The impact of volcanic aerosols on stratospheric chemistry with implications for geoengineering

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  1. The impact of volcanic aerosols on stratospheric chemistry with implications for geoengineering • Simone Tilmes (tilmes@ucar.edu) • WACCM team, Doug Kinnison, Rolando Garcia, Anne Smith, Ryan Neely, Andrew Conley, Jean-Francois Lamarque • Rolf Müller, Ross Salawitch, Tim Canty, Julia Jee-Taylor, Sasha Madronich, Kelly Chance SSiRC: 28 - 30 October 2013, Atlanta, Georgia, USA

  2. The impact of volcanic aerosols on stratospheric chemistry with implications for geoengineering • Impact of volcanic aerosols on total ozone • Changes in chemical reaction rates with enhanced aerosols • Importance of the aerosol distribution of polar ozone loss • Importance of very short-lived species on the example of geoengineering

  3. Column Ozone Change Ground based Observations, WMO 2006 Total ozone deviations from 1964-80 mean ElChichón MtPinatubo Observations, WMO 2010 • Volcanic aerosols have an important impact on ozone, result in a reduction of column ozone of about 3% for El Chichón and 5% for Mt Pinatubo • Influence up to 5 years

  4. Column Ozone Change NCAR WACCM CCMI Simulations Total ozone deviations from 1964-80 mean ElChichón ElChichón MtPinatubo MtPinatubo WACCM (SD) WACCM (no volcanoes, 2000-01 condition) Observations, WMO 2010 • WACCM results in slightly lower reduction (1-3%). Changes of chemistry do not explain reduced values of ozone 4 years after the eruption

  5. Impact on Ozone Destroying Cycles WACCM Ozone Change (1992) Surface Area Density (1992) ppm μm2/cm3 Difference Volcanic – Clean New SAD Dataset for CCMI NOx ClOx/BrOx HOx Ox, Total Loss • Increase of heterogeneous reactions • -> decrease of the NOx/NOy equilibrium (Fahey et al., 1993) • (1) N2O5 + H2O -> 2HNO3 • ClONO2 + H2O -> HOCl + HNO3 T < 200 K as important as (1) • ClONO2 + HCl-> HNO3 + Cl2 • HOCl + HCl -> Cl2 + H2O • -> increase in the ClOx, BrOx and HOx

  6. Impact on Ozone Destroying Cycles WACCM Ozone Change (1992) Surface Area Density (1992) ppm μm2/cm3 New SAD Dataset for CCMI Total Column change

  7. Arctic Polar Ozone Loss Estimation from Observations (HALOE satellite) Tilmes et al., 2008 • Ozone depletion depends on temperatures in the polar vortex • 1992, 1993: Low PSC Formation Potential, however larger Ozone Loss • Ozone depletion dependent on surface area density (Drdla and Müller, 2012) • 1992, 1993: line up in relation to ozone Are models able to simulate high ozone loss in 1993?

  8. Arctic Polar Ozone Loss WACCM Volcanic – Clean, March 1993 Estimation from Observations ~Impact of aerosols (~70DU) • expected impact of volcanic aerosols ~70 DU

  9. Arctic Polar Ozone Loss WACCM Volcanic – Clean, March 1993 Estimation from Observations ~Impact of aerosols (~70DU) Maximum around 40 DU • expected impact of volcanic aerosols ~70 DU (~30%) • simulated reduction around 40 DU Issue: prescribed surface area density field (monthly and zonal averages) are not in alignment with vortex dynamics SAD μm2/cm3

  10. Arctic Polar Ozone Loss WACCM Volcanic – Clean, March 1993 Estimation from Observations ~Impact of aerosols (70DU) Maximum around 40 DU Maximum around 65 DU • expected impact of volcanic aerosols ~70 DU (~30%) • simulated reduction around 40 DU Issue: prescribed surface area density field (monthly and zonal averages) are not in alignment with vortex dynamics • Modified SAD: Ozone loss up to 65 DU • MERRA temperatures too warm? SAD μm2/cm3 SAD from 1992 + increased high latitudes

  11. Impact of Geo-engineering SAD on Ozone in 2040 Impact of different assumptions of VSL halogens in the stratosphere % Change in Column Ozone Surface Area Density (2040) μm2/cm3 Rasch et al., 2008: 2Tg S yr-1, Tropical Injection 10oN-10oS % Difference Feb/March/April Aug/Sep/Oct Equivalent Latitude Equivalent Latitude • Considering the impact of VSLS on ozone loss: • Tropics: sign change with very short-lived species • Mid-latitudes: doubling of ozone loss; enhancement of the BrO and HOxcatalytic cycles • Polar LMS: significant increase of ozone loss; enhancement of BrOx and ClOx cycles Tilmes et al., 2012

  12. Impact of Geo-engineering SAD on Ozone in 2040 Impact of different assumptions of VSL halogens in the stratosphere % Change in Column Ozone Surface Area Density (2040) μm2/cm3 Rasch et al., 2008: 2Tg S yr-1, Tropical Injection 10oN-10oS % Difference Feb/March/April Aug/Sep/Oct Equivalent Latitude Equivalent Latitude • Considering the impact of VSLS on ozone loss: • Tropics: sign change with very short-lived species • Mid-latitudes: doubling of ozone loss; enhancement of the BrO and HOxcatalytic cycles • Polar LMS: significant increase of ozone loss; enhancement of BrOx and ClOx cycles Tilmes et al., 2012

  13. Summary • Volcanic aerosols impact global ozone for up to 5 years • Largest local reduction in the Arctic polar • Aerosol loading critical for models to estimate the impact of aerosols on ozone • Understanding of the amount of Chlorine and Bromine critical for impact of potential geoengineering applications on ozone

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