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Polar tropospheric ozone depletion – an overview

Polar tropospheric ozone depletion – an overview. Andrew Rankin British Antarctic Survey. Structure. Chemistry of tropospheric ozone depletion Previous campaigns Questions that remain. First observations. First reported in 1986 from observations at Barrow and Alert.

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Polar tropospheric ozone depletion – an overview

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  1. Polar tropospheric ozone depletion – an overview Andrew Rankin British Antarctic Survey

  2. Structure • Chemistry of tropospheric ozone depletion • Previous campaigns • Questions that remain

  3. First observations • First reported in 1986 from observations at Barrow and Alert • Soon demonstrated that O3 destruction was correlated with high filterable bromide Bottenheim et al., GRL 13, 113-116, 1986 Oltmans & Komhyr, JGR 91, 5229-5236 Barrie et al., Nature 334, 138-141, 1998

  4. Other observations • Ny-Alesund • Thule • Sondre-Stromfjord • Neumayer • Syowa • Arrival Heights

  5. Reactions to destroy ozone X + O3 XO + O2 Y + O3 YO + O2 XO + YO  X + Y + O2 • Catalytic cycle • X,Y can be any halogens – but Br is believed to be the prime species responsible. Barrie et al., Nature 334, 138-141, 1988

  6. Reactions to produce Br Photolysis of gaseous bromoform (Barrie et al, Nature 334, 138-141, 1988) ‘Bromide explosion’ BrO + HO2 HOBrg + O2 HOBrg  HOBraq HOBraq +Br- + H+ Br2aq + H2O Br2aqBr2g (Tang & McConnell,GRL 23, 2633-2636, 1996) Ozone + seawater ice O3 + Br- BrO- + O2 (Oum et al, GRL, 25, 3923-3926, 1998) Peroxymonosulphuric acid, free radicals (Mozurkewich, JGR 100, 14199-14207, 1995) Some Br lost by reaction with oxidised organics, or with HO2 (Fickert et al., JGR 104, 23719-23727, 1999)

  7. Possible sources of bromide Sea water • 67 ppm Br- • Mostly covered by sea ice in winter • Low relative surface area Frost flowers • 175ppm Br- • Common in winter • High surface area Snow • 0.003ppm • very high coverage throughout year • Very high surface area

  8. Polar Sunrise Experiment(s) • 1992, 1994, etc. • Centred at ALERT • First measurements of BrO by DOAS • Demonstrated role of Cl in ozone depletion was minor • Showed ozone depleted air masses came from over the polar ocean – associated with sea ice JGR special issue, 99, D12, 1994

  9. ARCTOC • Field studies at Ny Alesund 1995, 1996 – measured O3, XO, VOC etc. • also lab studies, modelling • Very similar findings to those at Alert • Showed BrO was the main species involved Arctic tropospheric ozone chemistry (ARCTOC), European Commision, 1997

  10. ALERT 2000 / SUMMIT 2000 • Concurrent studies at Alert and Summit (Greenland) • Large number of species measured • Results just published Atmos Env special issue, 36, 15-16, 2002

  11. TOPSE • Instrumented C-130 flown from Colorado to Northern Canada • Showed scale of ozone depleted areas, and association with sea ice

  12. GOME • Satellite measurements of BrO • High correlation with low 03 • High levels seen over sea ice Wagner et al., JGR, 106, 24,225-24,235, 2001

  13. Not just polar: Caspian sea… • In mid-latitudes, but also freezes in winter • High BrO observed by GOME

  14. …. And the Dead Sea • Low ozone events very similar to those seen in polar regions • Again correlated with high BrO • Salt flats believed to be the Br source Hebestrait et al., Science 283, 55-57, 1999

  15. Unanswered questions • Why is O3 depletion only seen in spring? • What is the source of the bromide: Snow / seawater / frost flowers? • Relative contribution of the various reactions proposed to release Bromide • Better characterisation of Antarctic depletion events Can CHABLIS help resolve some of these questions?

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