Chemical Box Models Markus Rex Alfred Wegener Institute Potsdam Germany (1) Basic concepts, simplified systems (Sunday) (2) The O x, NO y /NO x, HO x, Cl y /ClO x systems (Monday) (3) Application for polar ozone loss studies (Thursday)

bromine cycle (a)bromine cycle (b) M+ M Dominating ozone loss cycles for polar winter chemistry "ClO dimer cycle" M + M M need sunlight shuts down during night due to a lack of ClO 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 k ClO+ClO, but very sensitive on J Cl2O2 All cycles depend on [ClO x ] and sunlight

Polar ozone loss ClO + NO 2 -> ClONO 2 Cl + CH 4 -> HCl + CH 3 ClO + OH -> HCl + O 3 ClONO 2 + h -> ClO + NO 2 HCl + OH -> Cl + H 2 O

Polar ozone loss ClO + NO 2 -> ClONO 2 Cl + CH 4 -> HCl + CH 3 ClO + OH -> HCl + O 3 HCl + ClONO 2 -> Cl 2 + HNO 3 ClONO 2 + H 2 O -> HOCl + HNO 3 HNO 3 cold aerosol

Air mass trajectory (day/night) Lidar station Ozonsonde station Match project

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Match animation

15 Jan – 10 Feb K potential temperature Regression Ozone loss rate: /- 0.7 ppbv / sunlit hour Sunlit time [ hours ] Ozone change [ ppbv ] Rex et al., 1999

change of ozone only in sunlight no change in darkness => no significant dynamical bias Rex et al., GRL, 2003 Daytime loss vs. nightime loss  O 3 = L s. t s + L d. t d Loss rate during sunlit times sunlit time Bivariate regression analysis: Rate of change during darkness time in darkness

Schulz, et al.PhD work => Ozone loss occurs only in air masses that encountered PSC conditions during the past ten days. February: Lifetime of ClOx ~10 days

Filters build into the approach Rex et al., 1999 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

Effect of the filters Gross et al., 2003 Results of a virtual Match campaign within the CLAMS model => 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)

Match results  =475 K 2002 Warm winter, no campaign Ozon loss rate [ ppbv / day ] Date [ day of the year ] Area of potential PSC formation [ 10 6 km 2 ] 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.

ClO [ ppbv ] Potential temperature [ K ] Ozone column loss rate [ DU/ sunlit hour ] Potential temperature [ K ] ozone column loss rate [ DU/day ] (c) Ozone loss rate [ ppbv/day ] (b) Ozone loss rate [ ppbv/sunlit hour ] Ozone loss rates in Arctic winter 1999/2000 Date [ day of the year 2000 ] Rex et al., 2002

Potential temperature [ K ] Accumulated ozone column loss [ DU ] Date [ day of the year 2000 ] Spring equivalent potential temperature [ K ] Accumulated ozone loss [ ppmv ] Accumulated ozone loss [ ppmv ] Accumulated ozone loss in Arctic winter 1999/2000 Rex et al., 2002

Ozone loss rate [ ppbv / sunlit hour ] Denitrification in Arctic winter 1995/1996 Potentielle Temperatur [ K ] Ozonverlustrate [ ppbv / Tag ] [ ppbv / Sonnen- stunde ] Datum [ Tag des Jahres 1996 ] Model without denitrification 80% denitrification in 50% of the air masses Rex et al., Nature, 1997 => denitrification plays a significant role for severe Arctic ozone losses

Ozone loss versus V PSC Ozone column loss [ DU ] (14-25 km, mid-Jan to late March) Year Ozone column loss [ DU ] (14-25 km, mid-Jan to late March) Year Rex et al., GRL, 2004 ~ 15 DU additional ozone loss per Kelvin cooling of the Arctic stratosphere 5-6 K temperature change 80 DU ozone loss

Comparison with SLIMCAT – 2004 version With this version the sensitivity of Arctic ozone loss on climate change would be underestimated by a factor of three Ozone column loss [ DU ] (14-25 km, mid-Jan to late March) Year SLIMCAT Rex et al., GRL, 2004

Box model based on ClO x, BrO x, O x chemistry, run along Match trajectories to calculate ClO x that is required to explain the observed loss rates. January ozone loss – model => During cold Arctic Januaries ozone loss is consistently faster than can be explained with standard (JPL 2002) reaction kinetics max. available Cl y ClO x required to explain loss rate max. explainable loss rate observed loss rate Rex et al., GRL, 2003

Variation of ozone loss rate with sza (model) [ relative units ] Fraction of time spent per sza interval [% / deg ] Fraction of time spent per sza interval [% / deg ] Fraction of loss per sza interval [ % / deg ] sza [ deg ] Fraction of loss per sza interval [ % / deg ] Rex et al., 1999 Distribution of ozone loss vs. sza sensitivity to weak photolysis of Cl 2 O 2 in visible light. Not inconsistent with lab data. => Large effect on January ozone loss rates, weak effect in March

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  Cl2O2 in the relevant wavelength range +/- a factor of 8.6 for k eq ClO/Cl2O2 at 185 K. Day of the year ozone loss rate for complete activation [ppb/sunlit h] JPL2002 median +/- 34 % of the distribution => Factor of ~3 uncertainty (one  ) of the calculated ozone loss just due to uncertainty in the gas phase kinetic data. Frieler et al., PhD work

Sample same air mass at different sza during sunset => better constrain k eq ClO/Cl2O2 No measurement of Cl 2 O 2 needed (=> independent from Cl 2 O 2 uncertainties) No assumption about equilibrium Self-Match aircraft flight pattern Flight track 30 January 2003 outbound flight: before sunset inbound flight: after sunset airmasses probed during outbound leg

calculated matchradius COPAS (arbitrary units) Calculated matchradius + COPAS aerosol contrail encounters

Results from aircraft self Match 30 January 2003 MATCHES Equilibrium constant smaller than in JPL2002 ClO x calculated with box model from measured ClO Lifetime of ClO x long => simple model of only the ClO x family ClO/Cl 2 O 2 not in equilibrium ! => Calculations along trajectories

von Hobe et al., ACP, 2004 k eq Cl2O2/ClO K eq ClO/Cl2O2 derived from late night measurements close to equilibrium

SOLVE: Daytime Model Results JPL 2002 Huder & DeMore 1995 Burkholder 1990 Stimpfle et al., 2004 => Measurements by Burkholder (extrapolated to 450 nm) are more consistent with atmospheric observations of ClO and Cl 2 O 2 than current JPL recommendations Constraints on JCl 2 O 2 from combining atmospheric measurements of ClO and Cl 2 O 2 with box model calculations  Ratio = [ ClO model  ClO model ] / Cl 2 O 2 model [ ClO meas  ClO meas ] / Cl 2 O 2 meas  (J / k Prod ) model (J / k Prod ) actual

REPROBUS ~ WMO 2003 DOAS 18 February 2000 JPL02, 11% BrCl yield Bromine DOAS measurements of BrO (Pfeilsticker et al.) suggest more BrO x 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 -> BrCl + O 2 is ~11% (in JPL02: ~7%) => BrO x derived from measured BrO would further increase Canty et al.

Box model based on ClO x, BrO x, O x chemistry, run along Match trajectories to calculate ClO x that is required to explain the observed loss rates. January ozone loss – model During cold Arctic Januaries ozone loss is consistently faster than can be explained with standard (JPL 2002) reaction kinetics max. available Cl y ClO x required to explain loss rate max. explainable loss rate observed loss rate

With these changes the January ozone loss problem would be largely resolved. Kinetic data that is more consistent with recent field measurements of ClO and Cl 2 O 2 BrO x based on Pfeilsticker et al. January ozone loss - update Frieler et al., PhD work

Calculated ClO x vs. measured ClO x during SOLVE JPL 2002, standard bromine „new kinetic“, standard bromine „new kinetic“, high bromine ER-2 measurements Frieler et al., PhD work

Left: JPL02 kinetic Mid-left: „new“ kinetic Mid-right: JPL02 kinetic + „new“ BrO x Right: „new“ kinetic + „new“ BrO x ClO+ClO ClO+O ClO+BrO Fraction of ozone loss by individual loss cycles

Comparison with SLIMCAT – 2004 version With this version the sensitivity of Arctic ozone loss on climate change would be underestimated by a factor of three Ozone column loss [ DU ] (14-25 km, mid-Jan to late March) Year SLIMCAT old Rex et al., GRL, 2004

Comparison with SLIMCAT version New SLIMCAT version reproduces the slope (and degree of scatter !) reasonably well. Ozone column loss [ DU ] (14-25 km, mid-Jan to late March) Year Chipperfield et al, GRL, in press

Model uncertainties Day of the year ozone loss rate for complete activation [ppb/sunlit h] JPL2002 median +/- 34 % of the distribution with atmospheric ClO and Cl 2 O 2 measurements as additional constraint median +/- 34% of the distribution => Significant reduction in the model uncertainty if information from atmospheric measurements is used Frieler et al., PhD work 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  Cl2O2 in the relevant wavelength range +/- a factor of 8.6 for k eq ClO/Cl2O2 at 185 K.

Uncertainty in J ClOOCl with and without considering constraints by atmospheric measurements Normalized reaction constant (J ClOOCl / a priori median of J ClOOCl ) Cumulative probability a posteriori a piori... the median increases by ~55%... the uncertainty drops to ~35% of the a priori uncertainty Frieler et al., PhD work When considering constraints by atmospheric measurements...

“necessary ClO x ” ozone loss, 2ppb ClO x Main sources of uncertainties Relative contribution to uncertainty of model results [%] based on JPL constraints by atmospheric measurements Conatraints by atmospheric measurements strongly reduce the uncertainty of dimer photolysis to the total uncertainty In case of low chlorine activation the BrO + ClO -> BrO + ClOO reaction becomes the dominant source of uncertainty Frieler et al., PhD work

Evolution of A NAT compared to previous years  = 380 K  = 400 K  = 475 K  = 550 K

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 Ozone VMR loss profile 2005 vs Ozone loss [ ppmv ] 0123 potential temperature [ K ] / / /1999

Ozone loss estimates very sensitive to cooling rates and mixing issues  This region was excluded from previous column loss estimates Ozone loss [ molecules cm -3 ] 0246 Altitude [ km ] Ozone concentration loss profile 2005 vs / / /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.

Ozone column loss [ DU ] (14-25 km, mid-Jan to late March) V PSC [ 10 6 km 3 ] Year Ozone loss (14-25 km) vs. V PSC ( K)

Ozone column loss [ DU ] (14-25 km, mid-Jan to late March) V PSC [ 10 6 km 3 ] Year 2005 (preliminary !) Ozone loss (14-25 km) vs. V PSC ( K)

Ozone column loss [ DU ] ( K, mid-Jan to late March) V PSC [ 10 6 km 3 ] Year Ozone loss ( K) vs. V PSC ( K)

V PSC [ 10 6 km 3 ] Year 2005 (preliminary ! large uncertainties !!) Ozone column loss [ DU ] ( K, mid-Jan to late March) Ozone loss ( K) vs. V PSC ( K)

Long term evolution of V PSC Ozone loss [ DU ] Cold winters are getting significantly colder ! Reason ?? FU-Berlin data ECMWF ERA15 data Year V PSC [ 10 6 km 3 ]