Tropospheric ozone climatology at two Southern Hemisphere tropical/subtropical sites, (Reunion Island and Irene, South Africa) from ozonesondes, LIDAR, and in situ aircraft measurements

by G. Clain, J. L. Baray, R. Delmas, R. Diab, J. Leclair de Bellevue, P. Keckhut, F. Posny, J. M. Metzger, J. P. Cammas show all authors
Atmospheric Chemistry and Physics ()


This paper presents a climatology and trends of tropospheric ozone in\nthe Southwestern Indian Ocean (Reunion Island) and South Africa (Irene\nand Johannesburg). This study is based on a multi-instrumental dataset:\nPTU-O(3) ozonesondes, DIAL LIDAR and MOZAIC airborne instrumentation.\nThe seasonal profiles of tropospheric ozone at Reunion Island have been\ncalculated from two different data sets: ozonesondes and LIDAR. The two\nclimatological profiles are similar, except in austral summer when the\nLIDAR profiles show greater values in the free troposphere, and in the\nupper troposphere when the LIDAR profiles show lower values during all\nseasons. These results show that the climatological value of LIDAR\nprofiles must be discussed with care since LIDAR measurements can be\nperformed only under clear sky conditions, and the upper limit of the\nprofile depends on the signal strength.\nIn addition, linear trends have been calculated from ozonesonde data at\nReunion and Irene. Considering the whole tropospheric column, the trend\nis slightly positive for Reunion, and more clearly positive for Irene.\nTrend calculations have also been made separating the troposphere into\nthree layers, and separating the dataset into seasons. Results show that\nthe positive trend for Irene is governed by the lower layer that is\naffected by industrial pollution and biomass burning. On the contrary,\nfor Reunion Island, the strongest trends are observed in the upper\ntroposphere, and in winter when stratosphere-troposphere exchange is\nmore frequently expected.

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