# Presentation: 921236

## Impact of Laboratory Measurements of the ClOOCl Cross Section On Our Understanding of Polar Ozone Chemistry 

**T. Canty****1****, R. J. Salawitch****1****, **** ****R. M. Stimpfle****2****, **
**D. M. Wilmouth****2****, J. G. Anderson****2****, M. Rex****3****, **
**R. Schofield****3****, M. von Hobe****4****, M. Santee****5****, **
**D. Kinnison****6****, M. Kurylo****7****,  B.-M. Sinnhuber****8**
- 1University of Maryland, College Park, MD
- 2Harvard University, Cambridge, MA
- 3Alfred Wegener Institute for Polar and Marine Research, Pottsdam, Germany
- 4Institute for Chemistry and Dynamics of the Geosphere, Julich, Germany
- 5NASA Jet Propulsion Laboratory, Pasadena, CA
- 6National Center for Atmospheric Research, Boulder, CO
- 7University of Maryland, Baltimore County, Goddard Earth Sciences and Technology Center, MD
- 8University of Bremen, Bremen, Germany

## A study by Pope et al., JPC, 2007 reports measurements of the ClOOCl cross-section that challenge our understanding of polar chlorine chemistry. 

- WAVELENGTH (nm)

- JPL 2006

- Burkholder et al., 1990

- Huder and DeMore, 1995

- Pope et al., 2007

- ClOOCl Cross Section (cm2)

## Sensitivity to Treatment of Cl2 Interference

**No allowance for Cl****2**

**Largest allowance for Cl****2**

**Smallest allowance for Cl****2**

**Intermediate allowance for Cl****2**

- Courtesy, J. Burkholder, NOAA-ESRL

## ClOx Partitioning

- ClO + ClO + M → ClOOCl + M	: Rate = **k****FORWARD**  [ClO]2
-  ClOOCl + h → Cl + ClOO      	: Rate = **J** [ClOOCl]
-    ClOO + heat → Cl + Cl + O2
-       2 ( Cl + O3 → ClO + O2 )
-      Net:    2 O3 → 2 O2
-      Observations sensitive to kFORWARD and ClOOCl
-      Ozone loss occurs if ClOOCl is lost primarily by  photolysis (i.e.. T < ~210 K)
-      Photolysis is rate limiting step for ozone loss

- ClO + ClO + M → ClOOCl + M	: Rate = **k****FORWARD**[ClO]2
- ClOOCl + heat → ClO + ClO    	: Rate =** ****k****REVERSE**[ClOOCl]
-      Net: Null Cycle
-      Observations sensitive to kREVERSE / kFORWARD = KEQ
-      No ozone loss
-      Accurate measurement of ClO and precise knowledge of KEQ allows [ClOx] ([ClO]+2x[ClOOCl])
-      to be calculated: important for constraining ozone loss and for evaluating measurements
-      obtained during daytime for similar conditions

**Daytime**

**Nighttime**

## Sensitivity of Antarctic ozone loss to the ClOOCl cross section:

**JPL 2006**

**Burkholder 1990**

**Pope 2007**

**Huder & DeMore 1994**

- von Hobe et al., ACP, Phys., 7, 3055–3069, 2007

**Observed**
**Ozone**

- JPL 2006

## The Role of Halogen Chemistry in

***Polar Stratospheric Ozone Depletion***
**Objectives**:
- Evaluate consequences of new data on the ClO dimer photolysis rate on simulations of stratospheric ozone depletion, particular in winter polar regions.
- Evaluate old and new laboratory results for the photolysis rate and the type of further studies that are necessary to resolve current differences.
- Assess qualitative / quantitative evidence from the laboratory, field observations, & models linking ozone depletion to stratospheric active chlorine / bromine amounts.
**Implementation**:
- Workshop (Cambridge, UK – June 15 – 17, 2008) focused on Laboratory / Theory Studies, Atmospheric Measurements, & Modeling / Analysis Investigations
- Detailed workshop report in preparation
- Publications in each focus area to be assembled in a special journal issue (TBD) on a timescale suitable for use in the 2010 UNEP/WMO Ozone Assessment
**Organization:**
- Co-Chairs - M. J. Kurylo (UMBC/GEST) & B.-M. Sinnhuber (U. Bremen)
- Steering Group –
-  Laboratory/Theory: N. R. P. Harris  (U. Cambridge) & M. von Hobe (FZ Jülich)
- Atmospheric Measurements: P. A. Newman (NASA), D. W. Fahey (NOAA), & R.-S. Gao (NOAA)
- Modeling/Analysis: R. J. Salawitch (U. Maryland) & M. Chipperfield (U. Leeds)

## MOZART3/WACCM1b – Column Ozone Change

- 0 pptv Bry

- 22 pptv Bry

- Slide courtesy D. Kinnison

- Antarctic, 2005

- Arctic, 2004-05

- Mixing Ratio (ppb)

- ClO

- ClONO2

- HCl

- Inferred Cly (ppb)

- JPL2006

- ClOOCl (ppb)

**JPL2006 ****→ ****JPL 2006 kinetics**

**Aura Observations**

- Antarctic, 2005

- Arctic, 2004-05

- Mixing Ratio (ppb)

- ClO

- ClONO2

- HCl

- Inferred Cly (ppb)

- JPL2006

- ClOOCl (ppb)

- Stimpfle 2004

- JPL2006 → JPL 2006 kinetics
**Stimpfle 2004 ****→ ****J****ClOOCl**** Burkholder et al. 1990, K****eq****=Cox&Hayman, 1988, K****f****=Bloss *****et al.*****, 2001**

**Aura Observations**

- Antarctic, 2005

- Arctic, 2004-05

- Mixing Ratio (ppb)

- ClO

- ClONO2

- HCl

- Inferred Cly (ppb)

- JPL2006

- ClOOCl (ppb)

- Stimpfle 2004

- Huder&DeMore 1995

- JPL2006 → JPL 2006 kinetics
- Stimpfle 2004 → JClOOCl Burkholder et al. 1990, Keq=Cox&Hayman, 1988, Kf=Bloss *et al.*, 2001
**Huder & DeMore 1995 ****→ J****ClOOCl****  ****Huder and DeMore, 1995**

**Aura Observations**

- Antarctic, 2005

- Arctic, 2004-05

- Mixing Ratio (ppb)

- ClO

- ClONO2

- HCl

- Inferred Cly (ppb)

- JPL2006

- ClOOCl (ppb)

- Stimpfle 2004

- H&D1995

- Pope2007

- JPL 2006 → JPL 2006 kinetics
- Stimpfle 2004 → JClOOCl Burkholder et al., 1990, Keq=Cox&Hayman, 1988, Kf=Bloss *et al.*, 2001
- Huder & DeMore 1995 → JClOOCl  Huder and DeMore, 1995
**Pope 2007 ****→ J****ClOOCl**** ****Pope et al., 2007**

**Aura Observations**

## Rapid equilibrium between ClOOCl and ClClO2 (              )?

**Rapid equilibrium between ClOOCl and ClClO****2**** (              )?**

- ~10% of Cl2O2
- in the form of ClClO2 leads to “Burkholder like“ photolysis of the mixture
- Temperature dependent equilibrium could explain SOLVE / EUPLEX differences in ClO

- e.g. by:	ClOOCl + ClO → ClClO2 + ClO
- 	ClClO2 + ClO → ClOOCl + ClO

## Rapid equilibrium between ClOOCl and ClClO2 (              )?

**Rapid equilibrium between ClOOCl and ClClO****2**** (              )?**

- ~10% of Cl2O2
- in the form of ClClO2 leads to “Burkholder like“ photolysis of the mixture
- Temperature dependent equilibrium could explain SOLVE / EUPLEX differences in ClO

- e.g. by:	ClOOCl + ClO → ClClO2 + ClO
- 	ClClO2 + ClO → ClOOCl + ClO

- While the isomer is more thermally stable than the dimer, there are several reasons this chemistry is unlikely:
- 	Ab initio study does not support the formation of a complex from which ClClO2
-            can be formed from this reaction. – J. Hansen
- 	A re-analysis of ER-2 observations during SOLVE puts an
- 	upper limit on ClClO2 that is ***MUCH*** smaller than required
- 	for this chemistry to be noticeable – D. Wilmouth & R. Stimpfle
- 	ClClO2 would not photolyze in a manner that would
- 	lead to re-formation of O-O bond.

## A new study by von Hobe et al., RSC, 2008 (in review) reports

- measurements of the ClOOCl cross-section in matrix isolation
- that agree with results from the Huder and DeMore, 1995 study.

- WAVELENGTH (nm)

- JPL 2006

- Burkholder et al., 1990

- Huder and DeMore, 1995

- Pope et al., 2007

- ClOOCl Cross Section (cm2)

- Von Hobe et al., 2008

- Antarctic, 2005

- Arctic, 2004-05

- Mixing Ratio (ppb)

- ClO

- ClONO2

- HCl

- Inferred Cly (ppb)

- JPL2006

- ClOOCl (ppb)

- Stimpfle 2004

- H&D1995

- Pope2007

**Aura Observations**

- JPL 2006 → JPL 2006 kinetics
- Stimpfle 2004 → JClOOCl Burkholder et al., 1990, Keq=Cox&Hayman, 1988, Kf=Bloss *et al.*, 2001
- Huder & DeMore 1995 → JClOOCl  Huder and DeMore, 1995
- Pope2007 → JClOOCl Pope et al., 2007
**vonHobe 2008 → J****ClOOCl**** von Hobe et al., 2008**

- vonHobe 2008

## SOLVE

- A value of β=1 indicates good agreement between observations and models

- First measurements of ClOOCl from the ER-2 during SOLVE/THESEO-2000
- (Stimpfle *et al., JGR*, 2004)

## SOLVE

- Trolier *et al.*, 1990

- JPL2000

- Bloss *et al.*, 2001

- JPL2006

- Boakes *et al.*, 2005

- JClOOCl=Burkholder *et al*., 1994

- Kf

## SOLVE

- Trolier *et al.*, 1990

- JPL2000

- Bloss *et al.*, 2001

- JPL2006

- Boakes *et al.*, 2005

- JClOOCl=JPL06

- Kf

## SOLVE

- Trolier *et al.*, 1990

- JPL2000

- Bloss *et al.*, 2001

- JPL2006

- Boakes *et al.*, 2005

- JClOOCl=Huder and DeMore, 1995

- Kf

## SOLVE

- Trolier *et al.*, 1990

- JPL2000

- Bloss *et al.*, 2001

- JPL2006

- Boakes *et al.*, 2005

- JClOOCl=Pope *et al*., 2007

- Kf

## SOLVE

- Trolier *et al.*, 1990

- JPL2000

- Bloss *et al.*, 2001

- JPL2006

- Boakes *et al.*, 2005

- JclOOCl=von Hobe *et al*., 2008

- Kf

## Case Study: Segment of 2 February 2000ER-2 Flight Over Russia

- ClO/Cly

- (ClOx+ClONO2+HCl)/Cly

- 2xClOOCl/Cly

- HCl/Cly

**SLIMCAT MODEL**

## Model Constrained by Measured ClO

**JPL 2006 Chemistry**

## Model Constrained by Measured ClO

**Stimpfle Chemistry:**
**    ****Bloss k****F**
**      ****Burkholder ********ClOOCl**
**    ****Cox & Hayman (1988) K****EQ**

## Model Constrained by Measured ClO

**JPL 2006 Chemistry except**
**   ****Pope et al. (2007) ********ClOOCl**
**   ****JPL 2006 K****EQ**

## Conclusions (SPARC Polar Ozone Chemistry Workshop):

- 1. Quantification of Cl2 present in laboratory cell needed to reduce
-     uncertainty in the ClOOCl cross section
- 2. Chlorine isomer chemistry unlikely to be atmospherically
-     relevant: no other “missing chemistry/silver bullets” have yet
-     been established
- 3. Numerous observations of ClO and/or ClO & ClOOCl shown to be inconsistent with Pope et al. cross section ***and*** no other change to model chemistry
- 4. Accurate knowledge of KEQ combined with night time ClO can be used to calculate ClOx (ClO+2×ClOOCl):
- 		 If ClOx is “known”, constraints can be placed on JClOOCl from
-         measurements of ClO when the air mass experiences sunlight
-        Measurements of night time ClO not consistent with recommended
-         value of KEQ

## Thank You!

## Thank You!

- October 25, 2008

- New “Boss”