# Presentation: 504464

## Upper Stratospheric and Lower  Mesospheric HOx:Theory and Observations

***Upper Stratospheric and Lower  Mesospheric HO******x******:Theory and Observations***
**Tim Canty ****1****, Herb Pickett ****2****, Brian Drouin ****2****, Ken Jucks ****3****, Ross Salawith****2**

**HO****x**** Chemistry**

**1 ****University of Maryland, College Park, MD 20742**
**2 ****NASA Jet Propulsion Laboratory, Pasadena, CA 91109 **
**3**** Harvard Smithsonian Center for Astrophysics, Cambridge, MA  02138**

**                                                                                                                                                             ****Conclusions**

**Motivation**

**HO****x ****Dilemma**

**HO****x**** Dilemma Revisited**

**Ozone Deficit Problem**

**Ozone Deficit Problem - MLS**

**Affiliations and Acknowledgements**

- Two long standing problems in middle-atmospheric photochemistry
**HO****x**** Dilemma**: Before the MLS observations, models were unable to agree with available observations of  both stratospheric and mesospheric HOx (HOx=OH+HO2).  No combination of kinetic parameters could solve this issue.
**O****3**** Deficit Problem**: Models have a tendency to underestimate O3 at altitudes where O3 is controlled by HOx photochemistry.  Again, no combination of kinetic parameters have successfully resolved this issue.
- We re-examine both of these problems through the analysis of observational data
- and comparisons with photochemical model results.

- Model results agree with MLS OH observations without the need for changes to kinetics parameters as suggested in the literature (results do not exhibit a HOx dilemma)
- Taken at face value, our simulations suggest a continued need to resolve the ozone deficit problem without recourse to major perturbations in the kinetics parameters that regulate HOx

**Observations and Model Description**

- 1) Production
- 		Stratosphere	H2O + O(1D)  2OH
- 		Mesosphere	H2O + h  OH + H
- 2) Loss
- 				OH + HO2  H2O + O2
- 3) Partitioning (numerous)
- 				HO2 + O  OH + O2
- 				OH + O  O2 + H
- 				HOx + O3  products

**Observations****:**
**	****• **Microwave Limb Sounder (MLS): v2.2 retrievals of OH, HO2 and HOx pre-cursors
- 	• Balloon OH (BOH): functionally identical to THz module on MLS
- 	• Far-infrared Spectrometer (FIRS-2): Balloon-borne thermal emission far-infrared Fourier
- 	   transform spectrometer
- (for more info, see *Pickett et al.*, *GRL*, 2006, *Canty et al.*, *GRL*, 2006)
**1-D chemical model****:**
- 	• Assumes 24hr balance between production and loss
- 	• Constrained by MLS observations of O3,H2O, N2O, and temp.
- 	• JPL 2006 kinetics reproduces solar variability, improved Lyman-

- Ground based microwave observations of HO2 [*Clancy et al*. *JGR*, 1994] were used to suggest a 60-80% decrease in the rate of
- 	HO2 + O  OH + O2    (1)
- Mesospheric MAHRSI OH observations (*Summers et al., Science*, 1997) led to the suggestions of either decreasing (1) by 50% or reducing (1) by 20% and a 30% increase in
- 	HO2 +OH  H2O +O2   (2)

- _M_iddle _A_tmospheric _H_igh _R_esolution _S_pectrograph _I_nvestigation

- Standard model overpredicts OH at secondary peak (70km) and underpredicts OH at
- primary peak (40km)  (*Conway et al., GRL,* 27, 2000). No combination of kinetic parameters
- yields good agreement between models and measurements at all altitudes.

**NOTE**:  Without simultaneous observations of OH and HO2, it is difficult to attribute the above
- discrepancies to HOx loss, production, or partitioning.

- MLS zonal mean selected to match
- SZA range of MAHRSI (SZA=32°-49°)

- Above 45 km , MLS and MAHRSI 2σ uncertainties overlap.
- However, at the 70 km peak, MAHRSI is 20% lower than MLS.
- At the 42 km peak, MAHRSI is nearly 50% higher than MLS.

**Bottom Line:**
- Differences between observations could be related to the 8 year separation between observations and consequent changes in HOx pre-cursor species (O3, H2O, CH4, etc) .  Though it is unlikely that changes in the concentrations of the species would be large enough to explain the discrepancy between MLS and MAHRSI.

- Photochemical Loss O3 > Prod O3 , for  Z > ~45 km
- Hence, models tend to _underestimate _measured [O3]
- (*Jucks et al., JGR*, 1996, *Osterman et al., GRL,* 1997)
- Proposed solutions have not worked (see below).*	**GRL*, 1997

**Solutions?**
- • Vibrationally excited O2(*Miller et al.*, 1994)
- 	Collisional removal dominates photodissociation (Slanger and Copeland, 2003)
- • Rxn's involving vibrationally excited O2 and OH could solve HOx
-   dilemma as well (*Varandas*, 2004)
- 	Mechanism rate constants are insufficient to  produce significant changes (*Smith and Copeland*,  2005)
- • 50% decrease in O+HO2 (*Summers et al.*, 1997)
- 	Solves problem but leads to disagreement between models and observations of HOx (*Canty et al*., 2006)
- • OH tied up as HO3 (*Murray et al.*, *JPC*, 2007)
- 	Analysis only goes up to 30 km.  May lead to increase disagreement between models and observations of HOx

- Ox (Ox=O3+O) is controlled by HOx above 45 km.

- Model constrained to either MLS or FIRS-2 observations (H2O, O3, CH4, etc.) shows good agreement with observed OH and HO2(top panels)  The model uses standard JPL 2006 kinetics
- with modifications (within recommended uncertainty) to the rate of O+OH (Smith and Stewart, *J. Chem. Soc. Faraday Trans*.,1994) and OH+HO2(20% increase) to achieve overall good agreement between measured and modeled OH,HO2,HOx, and HO2/OH.
- However, the model over-predicts O3 loss above 45 km (bottom panels),where O3 photochemistry should be controlled by OH and HO2.  Slightly better agreement between model and MLS but for a very limited altitude range.

- MLS

- FIRS-2

- The fastest reactions involving HOX simply repartition
- the concentration of OH and HO2 without changing the overall amount of HOx.