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.

Ozonesonde measurements over Irene in South Africa are reported for the period 1990 to 1994 and a more recent period, 1998 to 2002, when the station became part of the Southern Hemisphere Additional Ozonesondes (SHADOZ) network. Irene displays the characteristic Southern Hemisphere springtime tropospheric ozone maximum, but its seasonal features are modulated by both tropical and midlatitude influences because of its location (25°54′S, 28°13′E) on the boundary of zonally defined meteorological regimes. The tropical savanna biomass burning signature, namely, the spring maximum, is less distinct in the lower troposphere than at stations closer to biomass burning source regions nearer the equator, although long‐range transport and recirculation in the subtropical anticyclonic gyre over southern Africa permit the buildup of relatively high springtime midtropospheric ozone. Midlatitude dynamical influences are evident, predominantly in winter when upper tropospheric ozone is enhanced as a result of stratospheric‐tropospheric injection of ozone. Mean tropospheric ozone values range between 40 and 60 ppbv throughout the year and increase by ∼20 ppbv in spring. The increase (∼10 ppbv) in surface and lower tropospheric ozone between the two time periods is attributed to an increase in urban‐industrial emissions. A classification of ozone profiles using a cluster analysis has enabled the delineation of a background and “most polluted” profile. Enhancements of at least 30% occur throughout the troposphere in spring, and in certain layers, increases close to 100% are observed.

Concern about health risks from sulfur dioxide (SO2) pollution prompted a health risk assessment for residents of the heavily polluted industrial region of South Durban, South Africa. The U.S. Environmental Protection Agency health risk assessment model was used to evaluate health effects for individuals in 4 age groups on the basis of data for a 3-yr period, from 1997-1999. Under normal exposure conditions, the level of risk was low (Hazard Quotient1); only under the worst-case scenario (exposure 24 hr/day) was there a significant risk of developing health effects. Inasmuch as these results are contrary to the popularly held belief that residents have a high risk of developing SO2-related respiratory diseases under normal exposure conditions, future studies should more thoroughly investigate exposure patterns and verify the authors' assumption that indoor SO2 levels are zero.