Rarity of upper-tropospheric low O3 mixing ratio events during MOZAIC flights W. A. H. Asman1, M. G. Lawrence1, C. A. M. Brenninkmeijer1, P. J. Crutzen1, J. W. M. Cuijpers2, and P. Nédélec3 1Max-Planck-Institute for Chemistry, Atmospheric Chemistry Division, P.O Box 3060, 55020 Mainz, Germany 2Royal Netherlands Meteorological Institute (KNMI), P.O. Box 201, 3730 AE De Bilt, The Netherlands 3Laboratoire d’Aérologie (UMR CNRS/UPS 5560) OMP, Université Paul Sabatier, 14 Avenue Edouard Belin, 31400 Toulouse, France
Abstract. Only a few previous observations of very low
O3 mixing ratios in the upper troposphere are available. The aim of this study was to examine the rich MOZAIC data set for more. Flights
with at least 25 4 s averaged mixing ratios less than 8 ppbv at pressures lower than
500 hPa measured using commercial aircraft within the MOZAIC project have been analysed. There
are eleven flights that fulfil these conditions (excluding artefacts as discussed below),
representing about 0.001% of all measurements during the analysed period August
1994-December 1997. The low O3
events occurred over Southeast Asia, Africa, Brazil and the sea area 200
km east of Florida (US) and were all likely to be associated with transport of air
masses from tropical sea areas. These low mixing ratio events occur in the upper troposphere
during periods with generally low mixing ratios. They are not only found over sea, but also
over land at pressure levels as low as 179 hPa. It could well be that some of the low
mixing ratio events measured during two or more flights belong to the same bigger low
mixing ratio area.
Citation: Asman, W. A. H., Lawrence, M. G., Brenninkmeijer, C. A. M., Crutzen, P. J., Cuijpers, J. W. M., and Nédélec, P.: Rarity of upper-tropospheric low O3 mixing ratio events during MOZAIC flights, Atmos. Chem. Phys., 3, 1541-1549, doi:10.5194/acp-3-1541-2003, 2003.