Ozone Variability and Trend Estimates from 20-Years of Ground-Based and Satellite Observations at Irene Station, South Africa

Abstract

While the stratospheric ozone protects the biosphere against ultraviolet (UV) radiation, tropospheric ozone acts like a greenhouse gas and an indicator of anthropogenic pollution. In this paper, we combined ground-based and satellite ozone observations over Irene site (25.90° S, 28.22° E), one of the most ancient ozone-observing stations in the southern tropics. The dataset is made of daily total columns and weekly profiles of ozone collected over 20 years, from 1998 to 2017. In order to fill in some missing data and split the total column of ozone into a tropospheric and a stratospheric column, we used satellite observations from TOMS (Total Ozone Mapping Spectrometer), OMI (Ozone Monitoring Instrument), and MLS (Microwave Limb Sounder) experiments. The tropospheric column is derived by integrating ozone profiles from an ozonesonde experiment, while the stratospheric column is obtained by subtracting the tropospheric column from the total column (recorded by the Dobson spectrometer), and by assuming that the mesospheric contribution is negligible. Each of the obtained ozone time series was then analyzed by applying the method of wavelet transform, which permitted the determination of the main forcings that contribute to each ozone time series. We then applied the multivariate Trend-Run model and the Mann–Kendall test for trend analysis. Despite the different analytical approaches, the obtained results are broadly similar and consistent. They showed a decrease in the stratospheric column (−0.56% and −1.7% per decade, respectively, for Trend-Run and Mann–Kendall) and an increase in the tropospheric column (+2.37% and +3.6%, per decade, respectively, for Trend-Run and Mann–Kendall). Moreover, the results presented here indicated that the slowing down of the total ozone decline is somewhat due to the contribution of the tropospheric ozone concentration.

Solar Ultraviolet Radiation in Pretoria and Its Relations to Aerosols and Tropospheric Ozone during the Biomass Burning Season

“…Although the changes in Simulation 3 were small compared to the reference simulation, increases in tropospheric ozone may result in decreases in UVR at the surface due to Rayleigh scattering of denser air in the lower levels as shown by other studies [63,64]. Positive decadal trends in tropospheric ozone have been identified over Pretoria [65,66] and these trends may further contribute to the radiative effect of tropospheric ozone.…”

Evolution of Ozone above Togo during the 1979-2020 Period

“…The multilinear regression (MLR) method was applied to study the interannual variability and trend of TOC over Togo. The MLR method used in this work is similar to that used in previous works [9,10,12]. The method was applied using the R statistical software [18].…”

“…Similarly, a decreasing ozone in the lower stratosphere in the tropical zone since 1998 has been observed [8]. The MLR method applied in several studies of the trend of variability of the TOC [9,10,11,12] is also used in this work to study TOC over Togo during the period 1979-2020. Togo is a West African country located in the intertropical zone between 6° N and 11° N, and between 0°14' W and 1°65' E. Being a stakeholder in the Montreal Protocol, Togo has made commitments not only to reduce Ozone Destruction Substances (ODS) emissions, but also to undertake ozone layer observation activities according to its supports funders.…”

Evolution of Ozone above Togo during the 1979–2020 Period

“…MSR-2 data were chosen because they are a gridded dataset allowing the collection of data specific to the territory of Togo. For the trend evaluation, we use a multilinear regression method that has been widely used for the analysis of the interannual and long-term contributions on total ozone datasets, the MLR method [25,[27][28][29].…”