Tropospheric ozone climatology over equatorial and Southern Africa using climate change parameters.

Abstract

Tropospheric ozone climatology over equatorial and southern Africa has been at the core of this study. SHADOZ (Southern Hemisphere ADditional OZonesondes) network data for the period 1998-2013, from Irene (South Africa) and Nairobi (Kenya), and MOZAIC (Measurement of OZone and water vapor by Airbus In service air Craft) programme data for the period 1998-2001 from Brazzaville (Congo) respectively have been used to investigate tropospheric ozone characteristics with regard to climate change parameters. These locations, which represent three different African climate zones including tropical (Brazzaville), equatorial (Nairobi) and subtropical (Irene) are poorly documented with regard to the variation and distribution of tropospheric ozone, although its levels over the region have been increasing since the last two decades of the twentieth century. With recent changes observed on climate parameters due to climate change, tropospheric ozone distribution and variability over this region have been investigated. Climate parameters including air temperature and relative humidity and ozone parameters such as partial pressure have been used to achieve the objective of this study. Results from tropospheric ozone modeling at Irene, using long term ozonesonde data from SHADOZ network, confirm the seasonal patterns of ozone, such as previously observed over southern Africa, with two maxima occurring in summer and spring respectively. However, increase on ozone concentrations from 55 to 65.6 DU in spring and from 32 to 55 DU in summer has been noted, in comparison with previous short term studies undertaken at this location. In the Congo Basin tropospheric ozone climatology investigated using short term aircraft data from MOZAIC programme collected at Brazzaville for the period 1998-2001 also presents two seasonal maxima occurring in August and February with 35.4 DU and 26.1 DU respectively. Over equatorial eastern Africa, which presents one of the most complex meteorogical system in the African continent, seasonal ozone distribution has also been noted with two peaks (43.0 DU) and (46.8 DU) occurring in July and October respectively. Analysis of case studies using HYSPLIT_4 (Hybrid Single-Particle Lagrangian Integrated Trajectory version 4) model and NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis model has shown that increase on tropospheric ozone over these regions is determined by precursor from both local and long range transport based from remote sources (biomass burning, lightning and biogenic emissions). The role played by dynamic processes is defined by positive divergence values and negative flux on zonal and meridional wind patterns prevailing at upper troposphere due to a quasi-permanent low pressure system prevailing in the region which in turn implies the highest partial ozone value observed in this region.