Abstract
Abstract. This paper presents a climatology and trends of tropospheric ozone in the Southwestern Indian Ocean (Reunion Island) and South Africa (Irene and Johannesburg). This study is based on a multi-instrumental dataset: PTU-O3 ozonesondes, DIAL LIDAR and MOZAIC airborne instrumentation. The seasonal profiles of tropospheric ozone at Reunion Island have been calculated from two different data sets: ozonesondes and LIDAR. The two climatological profiles are similar, except in austral summer when the LIDAR profiles show greater values in the free troposphere, and in the upper troposphere when the LIDAR profiles show lower values during all seasons. These results show that the climatological value of LIDAR profiles must be discussed with care since LIDAR measurements can be performed only under clear sky conditions, and the upper limit of the profile depends on the signal strength. In addition, linear trends have been calculated from ozonesonde data at Reunion and Irene. Considering the whole tropospheric column, the trend is slightly positive for Reunion, and more clearly positive for Irene. Trend calculations have also been made separating the troposphere into three layers, and separating the dataset into seasons. Results show that the positive trend for Irene is governed by the lower layer that is affected by industrial pollution and biomass burning. On the contrary, for Reunion Island, the strongest trends are observed in the upper troposphere, and in winter when stratosphere-troposphere exchange is more frequently expected.
Highlights
Ozone is a major greenhouse gas (Lacis et al, 1990), and tropospheric oxidant (Martin et al, 2003)
The tropospheric ozone budget is influenced by transport from the stratosphere and in situ photochemical production associated with ozone precursors emitted by anthropogenic activity, biomass burning and lightning (Stevenson et al, 2006)
In this study we have presented the climatology of tropospheric ozone in the south-western part of the Indian Ocean (Reunion Island) and South Africa (Irene, Johannesburg), and the tropospheric ozone trends
Summary
Ozone is a major greenhouse gas (Lacis et al, 1990), and tropospheric oxidant (Martin et al, 2003). Photochemical sources have been identified: biomass burning activity in Southern Africa and Madagascar during austral spring associated with long range transport of air masses are a cause of tropospheric ozone increase over Reunion Island (Baldy et al, 1996; Taupin et al, 2002). At this site, the influence of biomass burning activity has been identified between 5 and 12 km on tropospheric ozone profiles (Randriambelo et al, 2000). The ozone climatology and the long term trends have not been analyzed using the same approach at two tropical/subtropical sites in the region of Southern Africa and the Western Indian Ocean; this is the objective of the present study.
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