the impact of volcanic aerosols on stratospheric chemistry with implications for geoengineering...

The impact of volcanic aerosols on stratospheric chemistry with

implications for geoengineeringSimone 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

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

• 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

Column Ozone Change

Ground based Observations, WMO 2006

ElChichón

MtPinatubo

Observations, WMO 2010

Total ozone deviations from 1964-80 mean

WACCM (SD)WACCM (no volcanoes, 2000-01 condition)

ElChichón MtPinatubo

NCAR WACCM CCMI Simulations

• WACCM results in slightly lower reduction (1-3%). Changes of chemistry do not explain reduced values of ozone 4 years after the eruption

ElChichón

MtPinatubo

Column Ozone Change

Observations, WMO 2010

Total ozone deviations from 1964-80 mean

Increase of heterogeneous reactions-> decrease of the NOx/NOy equilibrium (Fahey et al., 1993)

(1) N2O5 + H2O -> 2HNO3

(2)ClONO2 + H2O -> HOCl + HNO3 T < 200 K as important as (1)

(3)ClONO2 + HCl -> HNO3 + Cl2

(4)HOCl + HCl -> Cl2 + H2O

-> increase in the ClOx, BrOx and HOx

Impact on Ozone Destroying CyclesSurface Area Density (1992) WACCM Ozone Change (1992)

Difference Volcanic – Clean NOxClOx/BrOx HOxOx,Total Loss

ppmμm2/cm3

New SAD Dataset for CCMI

Impact on Ozone Destroying CyclesSurface Area Density (1992) WACCM Ozone Change (1992) ppmμm2/cm3

New SAD Dataset for CCMI Total Column change

• Ozone depletion depends on temperatures in the polar vortex

• 1992, 1993: Low PSC Formation Potential, however larger Ozone Loss

Arctic Polar 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?

Estimation from Observations (HALOE satellite)

Tilmes et al., 2008

Arctic Polar Ozone LossEstimation from Observations WACCM Volcanic – Clean, March 1993

expected impact of volcanic aerosols ~70 DU

~Impact of aerosols (~70DU)

~Impact of aerosols (~70DU)

Arctic Polar Ozone LossEstimation from Observations WACCM Volcanic – Clean, March 1993

SAD μm2/cm3

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

Maximum around 40 DU

~Impact of aerosols (70DU)

Arctic Polar Ozone LossEstimation from Observations WACCM Volcanic – Clean, March 1993

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?

Maximum around 40 DU Maximum around 65 DU

SAD μm2/cm3

SAD from 1992 + increased high latitudes

% D

iffer

ence

Equivalent Latitude

Impact of Geo-engineering SAD on Ozone in 2040Impact of different assumptions of VSL halogens in the stratosphere

Feb/March/April

% Change in Column Ozone μm2/cm3

Rasch et al., 2008: 2Tg S yr-1, Tropical Injection 10oN-10oS

Surface Area Density (2040)

Aug/Sep/Oct

Equivalent Latitude

Tilmes et al., 2012Considering 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 HOx catalytic cycles-Polar LMS: significant increase of ozone loss; enhancement of BrOx and ClOx cycles

% D

iffer

ence

Equivalent Latitude

Impact of Geo-engineering SAD on Ozone in 2040Impact of different assumptions of VSL halogens in the stratosphere

Feb/March/April

% Change in Column Ozone μm2/cm3

Rasch et al., 2008: 2Tg S yr-1, Tropical Injection 10oN-10oS

Surface Area Density (2040)

Aug/Sep/Oct

Equivalent Latitude

Tilmes et al., 2012Considering 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 HOx catalytic cycles-Polar LMS: significant increase of ozone loss; enhancement of BrOx and ClOx cycles

• 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

Summary