2. Scientific Objectives
2.1 Background

2.2 Inorganic Chlorine chemistry
2.3 Bromine budget
2.4 HOx budget

2.5 Cirrus clouds

Background

Stratospheric ozone trend
35N-60N 1979 - 2004

Contribution to thecolumn O3 trend
in 1979-2004-1%-2%

WMO, 2006

0%(-3% for1992-1995
deficit)Controllingfactors
Gas phasephotochemistry

Dynamics &gas & het.
photochemistry(1/3 is due toexport of vortex air)

Further needs of systematic understandings of O3
chemistry and transport processes

Species and altitude range ofSMILES measurement
Day and night
Within clouds, too* Single scan with 3 km altitude resolution.
** Zonal mean average with 5 km altitude resolution

BackgroundScientific targets of SMILES
1. Inorganic Chlorine chemistry• ClO to HCl ratio• HOCl production• Global ClO
2. Bromine budget
3. HOx budget
4. Cirrus clouds
5. O3 isotope(6. UT/LS mixing(O3 trend in the US)(O3 trend in the LS)(background ClO)
(very short-lived source gas)

(HOx dilemma)(Het. reactions & Rad. budget)(mass independent chemistry)(O3 flux))

Partitioning within Cly in US

Chlorine chemistryobservations (SAGE, SBUV, Umkehr)model without (2)model with (2)1979-1990(WMO, 1998)

Cl + HO2 → HCl + O2
6%
ClO + OH → HCl + O2

(1)
(2)

Inclusion of the reaction(2) results in a better
agreement with observed[ClO]/[HCl] ratio (balloon )and O3 trend in the upper
stratosphere.

SMILES [ClO]/[HCl]measurements can beutilized further
systematic test on Cly
partitioning.

HOCl production

ClO + HO2 → HOCl + O2

Chlorine chemistry(Kovalenko et al, 2007)

There is a factor of 2 uncertainty in the rate constant for this reaction. It
directly affects HOCl levels, while it does not affect ClO and HO2 levels.

Chlorine chemistry

HOCl production
26 km

ClO + HO2 → HOCl + O2
HOCl + hv → OH + Cl
Cl + O3→ ClO + O2
OH + O3 → HO2 + O2
net 2O3 → 3O2
17 km(Kovalenko et al, 2007)

ClO+HO2 cycle can be the most efficient O3 loss processes within thecycles involving ClO in the LS, and therefore important for O3 trend.
SMILES HOCl measurements together with ClO and HO2 measurements
can be used to assess importance of the ClO+HO2 cycle.

Global ClO distribution?

Chlorine chemistry

The background ClOx level isimportant to quantify the insitu O3 loss at mid-latitudes.
However, its global
distribution has not been
observed with high precision.

Cl + CH4 → HCl + CH3
ClO + OH → HCl + O2
ClO + OH → Cl + HO2

6%
94%

1-5%
ClO + HO2 → HCl + O3
ClO + HO2 → HOCl + O2 95-99%

SMILES provides global ClO
distribution with highprecision. Furthermore,measurements of ClO, HCl,HOCl, and HO2 can provide
important insights into the Clychemistry.

Bromine budget
Bry from CH3Br & HalonsBromine budget+ 8 pptv Bry Source

BrO measurements suggest that in addition to long-lived source gases(halons and methyl bromide), very short-lived (τ < 6 months) sourcegases likely contribute to Bry by about 5 pptv. This difference can beimportant for O3 in the LS. (Salawitch et al., 2005)

Bromine budget
Bry fromCH3Br & Halons+ 5 pptv(WMO, 2006)

BrO + ClO & BrO + HO2 cycles

Bromine budget

MLS-derived Bry

Bry from CH3Br & Halons(Livesey et al., 2006)

SMILES BrO measurements provide further constraints to Brylevel, which affects O3 chemistry in the LS.

HOx budget

HOx budget(Canty et al., 2006)

HOx dilemma

JPL 2002

MLS(Conway et al., 2000)

HOx loss
HO2 + OH → H2O + O2 ⇒ +20%
OH/HO2 ratio
OH + O → H + O2 ⇒ increased

SMILES measurements will provide vertical profiles of HO2, which
can be used to test our understanding of HOx chemistry.

Cirrus clouds : Heterogeneous
reactions and radiation budget
MLS-derived
IWC at 147 hPa

January

July(Wu et al., 2008)

Cirrus clouds

20%Surface Area
Densityof Aerosols

ClO/ClyCirrus Clouds : Heterogeneous
reactions and radiation budget

Cirrus clouds-65°C

Temperature(Thornton et al., 2005)

Stratospheric O3 chemistry
ProductionLosshν
O2Ox = O + O3Ox

O3NOx

HNO3HOx

HO2
ClO, HCl,HOCl
BrO

ClOx
BrOx

Coupling
betweenradicals+ analyses on dynamics+ data from other satellites+ 3D CTM calculations(Wennberg et al., 1994)

Better understandingsof O3 trendSummary• Inorganic chlorine chemistry
Chlorine is the key species for O3 trend. SMILES provide major Cly species,including ClO, HCl, and HOCl. These data set will be utilized to test ourunderstanding in Cly chemistry, especially that affects O3 trend in the USand LS.
• Bromine budget
Very short-lived (τ<6 months) bromine containing species likely to beimportant for the budget of bromine, which plays significant role in O3chemistry. SMILES will provide useful constraint to study bromine budget.
• HOx budget
SMILES HO2 data can be utilized to test our understanding of HOxchemistry.
• Systematic understanding of O3 chemistry and transportCombination of high precision O3 data and those of related species will beutilized for overall test for the O3 chemistry (O3- NOx-ClOx-BrOx) andtransport (low-mid-latitudes) processes that control O3 levels.