Chemical Box Models

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Chemical Box Models Markus Rex Alfred Wegener
Institute Potsdam Germany
(1) Basic concepts, simplified systems
(Sunday) (2) The Ox, NOy/NOx, HOx, Cly/ClOx
systems (Monday) (3) Application for polar ozone
loss studies (Thursday)
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Dominating ozone loss cycles for polar winter
chemistry
All cycles depend on ClOx and sunlight
need sunlight
Red "rate limiting step" - the reaction with the
smallest rate or the "bottleneck" of the cycle.
Caution that does not tell us much about the
dynamics of the cycle. E.g. under twilight
conditions the ClO dimer cycle is surprisingly
insensitive to kClOClO, but very sensitive on
JCl2O2
shuts down during night due to a lack of ClO
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Polar ozone loss
ClO NO2 -gt ClONO2 Cl CH4 -gt HCl CH3 ClO
OH -gt HCl O3
ClONO2 hn -gt ClO NO2 HCl OH -gt Cl H2O
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Polar ozone loss
HNO3
cold aerosol
ClO NO2 -gt ClONO2 Cl CH4 -gt HCl CH3 ClO
OH -gt HCl O3
HCl ClONO2 -gt Cl2 HNO3 ClONO2 H2O -gt HOCl
HNO3
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Match animation
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15 Jan 10 Feb 1995470-500 K potential
temperature
Ozone change ppbv
Regression Ozone loss rate -5.5 /- 0.7 ppbv /
sunlit hour
Sunlit time hours
Rex et al., 1999
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Daytime loss vs. nightime loss
Bivariate regression analysis
Rate of change during darkness
time in darkness
DO3 Ls.ts Ld.td
sunlit time
Loss rate during sunlit times

• change of ozone only in sunlight
• no change in darkness
• gt no significant dynamical bias

Rex et al., GRL, 2003
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February Lifetime of ClOx 10 days
gt Ozone loss occurs only in air masses that
encountered PSC conditions during the past ten
days.
Schulz, et al.PhD work
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Filters build into the approach

• Divergence of trajectory cluster small
• avoids shear zones that tend to have larger
  mixing
• selects dynamical situations where trajectories
  are more reliable
• PV change along trajectory small
• avoids wave breaking events and unreliable
  trajectories
• Vertical gradient in ozone profiles small
• avoids lamina structures that indicate wave
  breaking and mixing
• makes results less sensitive on uncertainties in
  the calculates radiative cooling rates

Rex et al., 1999
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Effect of the filters
Results of a virtual Match campaign within the
CLAMS model gt Filters eliminate the bias
due to dynamical effects and reduce the
statistical uncertainty (broadness of the
distribution)
(Ozone loss rate derived from Match - real ozone
loss rate in the model)
Gross et al., 2003
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Match results 1992-2003 Q475 K
Area of potential PSC formation 106 km2
Ozon loss rate ppbv / day
2002 Warm winter,no campaign
2003
-30
Date day of the year
Rex, 1993 von der Gathen, et al., Nature, 1995
Rex et al. Nature, 1997 Rex et al., JGR, 1998
Rex et al., JAC, 1999 Rex et al., JGR, 2002
Schulz, et al., GRL, 2000 Schulz et al., JGR,
2001, Streibel et al., submitted.
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Ozone loss rates in Arctic winter 1999/2000
(c) Ozone loss rate ppbv/day
(b) Ozone loss rate ppbv/sunlit hour
ClO ppbv
Potential temperature K
Potential temperature K
ozone column loss rate DU/day
Ozone column loss rate DU/ sunlit hour
Date day of the year 2000
Date day of the year 2000
Rex et al., 2002
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Accumulated ozone loss in Arctic winter 1999/2000
Accumulated ozone loss ppmv
Spring equivalent potential temperature K
Potential temperature K
Accumulated ozone column loss DU
Accumulated ozone loss ppmv
Date day of the year 2000
Rex et al., 2002
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Denitrification in Arctic winter 1995/1996
Ozone loss rate ppbv / sunlit hour
Potentielle Temperatur K
Model
without denitrification
ppbv / Sonnen- stunde
80 denitrification
80 denitrification in 50 of the air masses
Ozonverlustrate
gt denitrification plays a significant role for
severe Arctic ozone losses
ppbv / Tag
Datum Tag des Jahres 1996
Rex et al., Nature, 1997
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Ozone loss versus VPSC
Year
Year
Ozone column loss DU (14-25 km, mid-Jan to
late March)
Ozone column loss DU (14-25 km, mid-Jan to
late March)
Rex et al., GRL, 2004
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SLIMCAT
Rex et al., GRL, 2004
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January ozone loss model
Box model based on ClOx, BrOx, Ox chemistry, run
along Match trajectories to calculate ClOx that
is required to explain the observed loss rates.
ClOx required to explain loss rate
max. available Cly
max. explainable loss rate
observed loss rate
gt During cold Arctic Januaries ozone loss is
consistently faster than can be explained with
standard (JPL 2002) reaction kinetics
Rex et al., GRL, 2003
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Variation of ozone loss rate with sza (model)
relative units
Distribution of ozone loss vs. sza
Fraction of time spent per sza interval / deg
Fraction of loss per sza interval / deg
Fraction of time spent per sza interval / deg
Fraction of loss per sza interval / deg
sza deg
Rex et al., 1999
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Model uncertainties
Monte Carlo simulations of model
uncertainties hundreds of model runs distributed
according to the stated uncertainties in
JPL2002 e.g. /- a factor of 3 for sCl2O2 in the
relevant wavelength range /- a factor of 8.6 for
keq ClO/Cl2O2 at 185 K . . .
JPL2002 median /- 34 of the distribution
ozone loss ratefor complete activation
ppb/sunlit h
Day of the year
gt Factor of 3 uncertainty (one s) of the
calculated ozone lossjust due to uncertainty in
the gas phase kinetic data.
Frieler et al., PhD work
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Self-Match aircraft flight pattern

• Sample same air mass at different sza during
  sunset gt better constrain keq ClO/Cl2O2
• No measurement of Cl2O2 needed (gt independent
  from Cl2O2 uncertainties)
• No assumption about equilibrium

Flight track 30 January 2003
outbound flightbefore sunset
inbound flight after sunset
airmasses probed during outbound leg
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Calculated matchradius COPAS aerosol
contrail encounters
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Results from aircraft self Match 30 January 2003

• ClOx calculated with box model from measured ClO
• Lifetime of ClOx long gt simple model of only the
  ClOx family
• ClO/Cl2O2 not in equilibrium ! gt Calculations
  along trajectories

Equilibrium constant smallerthan in JPL2002
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Keq ClO/Cl2O2 derived from late night
measurements close to equilibrium
von Hobe et al., ACP, 2004
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SOLVE Daytime Model Results
Constraints on JCl2O2 from combining atmospheric
measurements of ClO and Cl2O2 with box model
calculations
gt Measurements by Burkholder (extrapolated to
450 nm) are more consistent with atmospheric
observations of ClO and Cl2O2 than current JPL
recommendations
Stimpfle et al., 2004
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Bromine

• DOAS measurements of BrO (Pfeilsticker et al.)
  suggest more BrOx than can be explained by long
  lived source gases
• Canty et al. Low OClO measurements during night
  suggest that the branching ratio of ClO BrO
  -gt BrCl O2 is 11 (in JPL02 7)gt BrOx
  derived from measured BrO would further increase

Canty et al.
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January ozone loss model
Box model based on ClOx, BrOx, Ox chemistry, run
along Match trajectories to calculate ClOx that
is required to explain the observed loss rates.
During cold Arctic Januaries ozone loss is
consistently faster than can be explained with
standard (JPL 2002) reaction kinetics
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January ozone loss - update

• Kinetic data that is more consistent with recent
  field measurements of ClO and Cl2O2
• BrOx based on Pfeilsticker et al.

With these changes the January ozone loss problem
would be largely resolved.
Frieler et al., PhD work
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Calculated ClOx vs. measured ClOx during SOLVE
JPL 2002, standard bromine
new kinetic, standard bromine
new kinetic, high bromine
ER-2 measurements
Frieler et al., PhD work
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Fraction of ozone loss by individual loss cycles
Frieler et al., PhD work
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SLIMCAT old
Rex et al., GRL, 2004
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Chipperfield et al, GRL, in press
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Model uncertainties
Monte Carlo simulations of model
uncertainties hundreds of model runs distributed
according to the stated uncertainties in
JPL2002 e.g. /- a factor of 3 for sCl2O2 in the
relevant wavelength range /- a factor of 8.6 for
keq ClO/Cl2O2 at 185 K . . .
JPL2002 median /- 34 of the distribution
ozone loss ratefor complete activation
ppb/sunlit h
Day of the year
Frieler et al., PhD work
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Uncertainty in JClOOCl with and without
considering constraints by atmospheric
measurements
When considering constraints by atmospheric
measurements ...
a piori
Cumulative probability

• ... the median increases by 55
• ... the uncertainty drops to 35 of the a priori
  uncertainty

a posteriori
Normalized reaction constant (JClOOCl/ a priori
median of JClOOCl)
Frieler et al., PhD work
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Main sources of uncertainties
Relative contribution to uncertainty of model
results
based on JPL2002
ozone loss, 2ppb ClOx
necessary ClOx
constraints by atmospheric measurements
0 20 40 60 80 100
0 20 40 60 80 100
Frieler et al., PhD work
Conatraints by atmospheric measurements strongly
reduce the uncertainty of dimer photolysis to the
total uncertainty In case of low chlorine
activation the BrO ClO -gt BrO ClOO reaction
becomes the dominant source of uncertainty
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Evolution of ANAT compared to previous years
Q 380 K
Q 475 K
Q 400 K
Q 550 K
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Ozone VMR loss profile 2005 vs. 2000
1999/2000
1998/1999
2004/2005

• Maximum loss in 1999/2000 at about 460 K, Ioss in
  2004/2005 peaked lower down at 420 K
• At all levels below 440 K loss in 2004/2005 was
  larger than in 1999/2000

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Ozone concentration loss profile 2005 vs. 2000
1999/2000
2004/2005
1998/1999

• In terms of concentration ozone loss in
  2004/2005 larger than the previous record from
  1999/2000.
• Column loss in 2004/2005 also larger than in
  1999/2000.

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Ozone loss (14-25 km) vs. VPSC (400-550 K)
Year
Ozone column loss DU (14-25 km, mid-Jan to
late March)
VPSC 106 km3
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Ozone loss (14-25 km) vs. VPSC (400-550 K)
Year
Ozone column loss DU (14-25 km, mid-Jan to
late March)
2005 (preliminary !)
VPSC 106 km3
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Ozone loss (360-550 K) vs. VPSC (360-550 K)
Year
Ozone column loss DU (360-550 K, mid-Jan to
late March)
VPSC 106 km3
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Ozone loss (360-550 K) vs. VPSC (360-550 K)
Year
Ozone column loss DU (360-550 K, mid-Jan to
late March)
2005 (preliminary ! large uncertainties !!)
VPSC 106 km3
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Long term evolution of VPSC
FU-Berlin data
ECMWF ERA15 data
VPSC 106 km3
Ozone loss DU
Year
Cold winters are getting significantly colder !
Reason ??