RESEARCH LETTERS

 

Elevated ozone events over Johannesburg based on analysis of tropospheric ozone partial columns

 

 

Atham Raghunandan^{I, II}; Gilberto Mahumane^{II, III}; Roseanne Diab^II

^IPresent address: CSIR Natural Resources and the Environment, P.O. Box 17001, Congella 4013, South Africa. E-mail: araghunandan@csir.co.za
^IISchool of Environmental Sciences, University of KwaZulu-Natal, Howard College Campus, Durban 4041, South Africa
^IIIOn study leave from Department of Physics, Eduardo Mondlane University, Maputo, Mozambique

 

 

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ABSTRACT

Traditionally, tropospheric column ozone (TCO) is a useful indicator for comparing both temporal and spatial variations in tropospheric ozone. TCO variations over Johannesburg are analysed in this paper with a view to identifying days of enhanced ozone, which could then form the basis of a detailed investigation to determine sources of the elevated ozone. We used ozone data from the Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft (MOZAIC) database for the period 1995 to 1998. A fixed tropopause height of 12 km was employed in this analysis as the upper bound of the troposphere. Seasonal and inter-annual variations in TCO provided a context for this study. A clear seasonal cycle exists, with TCO peaking in September and October. Minimum TCO occurs in autumn, when variability is also least. The lower day-to-day variability in autumn and winter is a reflection of the more settled weather at this time. This period is representative of background tropospheric ozone loadings, on which the dynamic and photochemical influences of other months are superimposed. High-TCO events, defined as exceeding 30 DU (Dobson units), occurred predominantly in spring. Enhancements in the lower troposphere are shown to be generally short-lived (1-2 days) and due to the effects of local surface pollution sources, and arise most likely from biomass burning, which peaks in spring. In contrast, events in the upper troposphere prevailed for a longer period and were due to the penetration of ozone-rich air from the stratosphere, as shown in a case study in September 1998.

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References

1. Zbinden R.M., Cammas J-P., Thouret V., Nédélec P., Karcher F. and Simon P. (2006). Mid-latitude tropospheric ozone columns from the MOZAIC program: climatology and interannual variability. Atmos. Chem. Phys. Discuss. 6, 1053-1073.         [ Links ]

2. Diab R.D., Thompson A.M., Zunckel M., Coetzee G.J.R., CombrinkJ., Bodeker G.E., Fishman J., Sokolic F., McNamara D.P, Archer C.B. and Nganga D. (1996). Vertical ozone distribution over southern Africa and adjacent oceans during SAFARI-92. J. Geophys. Res. 101(D19), 23823-23833.         [ Links ]

3. Logan J.A. (1985). Tropospheric ozone: seasonal behavior, trends, and anthropogenic influence. J. Geophys. Res. 90(D6), 10463-10482.         [ Links ]

4. Olson J.R., Fishman J., Kirchhoff V.W.J.H. Nganga D. and Cros B. (1996). Analysis of the distribution of ozone over the southern Atlantic region. J. Geophys. Res. 101 (D19), 24083-24093.         [ Links ]

5. Oltmans S.J., Galbally I.E., Brunke E-G., Meyer C.P., Lathrop J.A., Johnson B.J., Shadwick D.S., Cuevas E., Schmidlin, F.J., Tarasick D.W., Claude H., Kerr J.B., Uchino O. and Mohnen V (1998). Trends of ozone in the troposphere. Geophys. Res. Lett. 25(2), 139-142.         [ Links ]

6. Thompson A.M., Witte J.C., McPeters R.D., Oltmans S.J., Schmidlin F.J., Logan J.A., Fujiwara M., Kirchhoff V.W.J.H., Posny F., Coetzee G.J.R., Hoegger B., Kawakami S., Ogawa T, Johnson B.J., Vömel H. and Labow G. (2003). Southern Hemisphere Additional Ozonesondes (SHADOZ) 1998-2000 tropical ozone climatology 1. Comparison with Total Ozone Mapping Spectrometer (TOMS) and ground-based measurements. J. Geophys. Res. 108(D2), 10-1-10-19.         [ Links ]

7. Thompson A.M. and Hudson R.D. (1999). Tropical tropospheric ozone (TTO) maps from Nimbus 7 and Earth Probe TOMS by the modified-residual method: evaluation with sondes, ENSO signals, and trends from Atlantic regional time series. J. Geophys. Res. 104(D21), 26961-26975.         [ Links ]

8. Cros B., Nganga D., Minga A., Fishman J. and Brackett V. (1992). Distribution of tropospheric ozone at Brazzaville, Congo, determined from ozonesonde measurements. J. Geophys. Res. 97(D12), 12869-12875.         [ Links ]

9. Thompson A.M., Diab R.D., Bodeker G.E., Zunckel M., Coetzee G.J.R., Archer C.B., McNamara D.P., Pickering K.E., Combrink J., Fishman J. and Nganga D. (1996). Ozone over southern Africa during SAFARI-92/TRACE A. J. Geophys. Res. 101(D19), 23793-23807.         [ Links ]

10. Cahoon D.R., Stocks B.J., Levine J.S., Cofer W.R. and O'Neill K.P (1992). Seasonal distribution of African savanna fires. Nature 359, 812-815.         [ Links ]

11. Thompson A.M., Pickering K.E., McNamara D.P., Schoeberl M.R., Hudson R.D., Kim J.H., Browell E.V., Kirchoff VWJ.H. and Nganga D. (1996b). Where did tropospheric ozone over southern Africa and the tropical Atlantic come from in October 1992? Insights from TOMS, GTE TRACE A, and SAFARI 1992. J. Geophys. Res. 101, 24251-24278.         [ Links ]

12. Garstang M., Tyson P.D., Swap R., Edwards M., Kallberg P. and Lindesay J.A. (1996). Horizontal and vertical transport of air over southern Africa. J. Geophys. Res. 101(D19), 23721-23736.         [ Links ]

13. Marenco A., Thouret V., Nedéléc P., Smit H., Helten M., Kley D., Karcher F., Simon P., Law K., Pyle J., Poschmann G., Wrede R.V., Hume C. and Cook T (1998). Measurement of ozone and water vapour by Airbus in-service aircraft: the MOZAIC airborne program, an overview. J. Geophys. Res. 103(D19), 25631-25642.         [ Links ]

14. Thouret V, Marenco A., Nedéléc P. and Grouhel C. (1998). Ozone climatologies at 9-12 km altitude as seen by the MOZAIC airborne program between September 1994 and August 1996. J. Geophys. Res. 103(D19), 25653-25679.         [ Links ]

15. MOZAIC-II: Technical Final Report (1996-1999) (2000). January 2000. University of Paul Sabatier, Toulouse, France.         [ Links ]

16. Cosijn C. and Tyson P.D. (1996). Stable discontinuities in the atmosphere over South Africa. S. Afr. J. Sci. 92, 381-386.         [ Links ]

17. Reiter E.R. (1975). Stratospheric-tropospheric exchange processes. Rev. Geophys Space Phys 13(4), 459-473.         [ Links ]

18. Staley D.O. (1962). On the mechanism of mass and radioactivity transport from the stratosphere to troposphere. J. Atmos. Sci. 19, 450-467.         [ Links ]

19. Danielsen E.F. (1968). Stratospheric-tropospheric exchange based on radioactivity, ozone and potential vorticity. J. Atmos. Sci. 25, 502-518.         [ Links ]

20. Reed R. (1955). A study of a characteristic type of upper-level frontogenesis. J. Meteorol. 12, 226-237.         [ Links ]

21. World Meteorological Organisation (WMO) (1986). Atmospheric ozone. Report 36, Geneva.         [ Links ]

22. Bethan S., Vaughan G. and Reid S.J. (1996). A comparison of ozone and thermal tropopause heights and the impact of tropopause definition on quanfying the ozone content of the troposphere. Q. J. R. Met. Soc. 122, 929-944.         [ Links ]

23. Cammas J-P., Jacoby-Koaly S., Suhre K., Rosset R. and Marenco A. (1998). Atlantic subtropical potential vorticity barrier as seen by Measurements of Ozone by Airbus In-Service Aircraft (MOZAIC) flights. J. Geophys. Res. 103 (D19), 25681-25693.         [ Links ]

24. Thompson A.M., Witte J.C., Oltmans S.J., Schmidlin F.J., Logan J.A., Fujiwara M., Kirchoff VW.J.H., Posny F., Coetzee G.J.R., Hoeger B., Kawakami S., Ogawa T, Fortuin J.P.F. and Kelder H.M. (2003). Southern Hemisphere Additional Ozonesondes (SHADOZ) 1998-2000 tropical ozone climatology. 2, Tropospheric variability and the zonal wave-one. J. Geophys. Res. 108(D2), 8241-8262.         [ Links ]

25. Zunckel M., Diab R.D. and Scourfield M.W.J. (1992). Vertical distribution of ozone at Pretoria: comparisons between 1965-68 and 1990-1991. The Clean Air J. 8, 3-8.         [ Links ]

26. Combrink J., Diab R.D., Sokolic F. and Brunke E.G. (1995). Relationship between surface, free tropospheric and total column ozone in two contrasting areas in South Africa. Atmos. Environ. 29(6), 685-691.         [ Links ]

27. Diab R., Barsby J., Bodeker G., Scourfield M. and Salter L. (1992). Satellite observations of total ozone above South Africa. S. Afr. Geog. J. 74, 13-18.         [ Links ]

28. Diab R.D., Thompson A.M., Mari K., Ramsay L. and Coetzee G.J.R. (2004). Tropospheric ozone climatology over Irene, South Africa from 1990-1994 and 1998-2001. J. Geophys. Res. 109, D20301, doi:10.1029/2004JD004793, 2004.         [ Links ]

29. Baldy S., Ancellet G., Bessafi M., Badr A. and Lan Sun Luk D. (1996). Field observations of the vertical distribution of tropospheric ozone at the island of Réunion (southern tropics). J. Geophys. Res. 101(D19), 23835-23849.         [ Links ]

30. Nganga D., Minga A., Cros B., Bouka Biona C., Fishman J. and Grant W.B. (1996). Ozone over southern Africa during SAFARI-92/TRACE A. J. Geophys. Res. 101(D19), 24095-24103.         [ Links ]

31. Raghunandan A. (2003). Nature and characteristics of tropospheric ozone over Johannesburg. M.A. thesis, University of Natal, Durban.         [ Links ]

32. Tyson P.D., Garstang M., Thompson A.M., Diab R.D., Browell E.V. and D'Abreton P.C. (1997). Correspondence between ozone measurements, transport and production of ozone over south central Africa. J. Geophys. Res. 102(D9), 10623-10636.         [ Links ]

33. Mahumane G. (2002). Analysis of high ozone events over Africa. M.Sc. thesis, Univerisity of Natal, Durban.         [ Links ]

34. Holton J.R., Haynes P.H., McIntire M.E., Douglass A.R., Rood R.B. and Pfister L. (1995). Stratospheric-tropospheric exchange. Rev. Geophys. 33, 403-439.         [ Links ]

35. Baray J.L., Ancellet G., Taupin F.G., Bessafi M., Baldy S. and Keckhut P. (1998). Subtropical tropopause break as a possible stratospheric source of ozone in the tropical troposphere. J. Atmos. Sol.-Terr. Phys. 60, 27-36.         [ Links ]

 

 

Received 19 March2007.
Accepted 26 June 2007.

 

 

*Author for correspondence. E-mail: diab@ukzn.ac.za