Studies have established that extreme air pollution is more prevalent and is responsible for more deaths and disability-adjusted life years (DALY) in urban cities, especially in developing economies. However, the paucity of ground-based observation has greatly hindered extensive and long-term monitoring and, as such, a good understanding of the trend and characteristics of air quality where it matters most. Aerosol optical depth (AOD) from satellites retrievals provides good spatial and temporal resolutions of atmospheric aerosols and could be a good proxy for ground-level PM_2.5 concentration. This study used a Bayesian regression model to determine the parameters of a PM_2.5 model at four monitoring stations using AOD and selected atmospheric variables (PBLH and RH) as input. The dry-air reference value (K) and the integrated humidity coefficient (γ) were used to delineate the effects of the aerosol characteristics. The values of K and γ, $0.02<K<0.07$ (${\mathrm{m}}^2{\mathrm{g}}^{\mathrm{-1}}$) and $0.54<\gamma <3.14$, respectively, are site-specific even within the same country as is the case for Lekki and Benin (both in Nigeria). The PM_2.5 estimates from the developed observation-based model were in good agreement with the ground-based observations ($0.55<r<0.77$). RH and a combination of PBLH-RH were the best performers in the development of the model. Firstly, this study identifies the unique range of values for K and $\gamma$ for site-classes in the sub-Saharan tropical climate. Secondly, PBLH adds more explanatory power to the PM_2.5 estimates in Benin and Douala (both non-coastal cities) while RH improves the performance of the model significantly in Lekki and Owendo (both coastal cities). For West Africa and similar data-sparse regions, the methodology presented here offers a practical pathway to enhance air quality monitoring capabilities.

Regional Total Electron Content (TEC) Maps proffer better mitigation effects in ionospheric models which are needed to resolve ionospheric TEC gradient errors associated with space-based technologies such as Global Navigation Satellite Systems (GNSS) and Space-Based Augmentation Systems (SBAS). EGNOS (European Geostationary Navigation Overlay System) is a European SBAS system that provides integrity, accuracy, continuity and availability to critical GNSS applications like aviation and others over ECAC (European Civil Aviation Conference) area. The EGNOS Ionospheric model is built with the concept of the ordinary Planar fit technique. This paper focuses on modified Planar fit, ordinary Kriging and modified Kriging techniques to validate the EGNOS algorithm during different geophysical (geomagnetically quiet and disturbed) conditions. The structure of EGNOS was strictly adhered to during the study and only publicly available GNSS ground-based stations over the ECAC area are engaged in the study. The preliminary results obtained show that adapting modified Planar fit and Kriging techniques could improve the EGNOS services over the ECAC area, most especially the northern part near the high latitudes and the southern part near the low latitude regions.

The effect of the main phase of two intense geomagnetic storm events which occurred on August 5 - 6 and September 26 - 27, 2011 on the equatorial ionosphere have been investigated using Global Positioning System (GPS) data obtained from an Ile-Ife station (geomagnetic lat. \ang{9.84}N, long. 77.25 degree E, Dip \ang{7.25}N). Total Electron Content (TEC) profiles during the main phase of the two geomagnetically disturbed days were compared with quiet time average profiles to examine the response of the equatorial ionosphere. The results showed that the intensity of both storm events during the main phase which occurred at night-time correlated well with a strong southward direction of the z-component of the Interplanetary Magnetic Field (IMF-Bz) and Solar Wind Speed (Vsw), with the Disturbance storm time (Dst) profile showing multiple step development. TEC depletion was observed during the main phase of the August 5 - 6, 2011 storm event with TEC recording a maximum value of 9.31 TECU. A maximum TEC value of 55.8 TECU was recorded during the main phase of the September 26 - 27, 2011 storm event depicting TEC enhancement. Significant scintillation index value of 0.57 was observed when the main phase started on August 5 - 6, 2011 followed by a prolonged suppression while there was less significant scintillation impact on September 26 - 27, 2011 with a maximum value of 0.33. The present study show that rapid energy input from solar wind during geomagnetic storm events effect large variations in TEC and significant scintillation phenomenon in the equatorial ionosphere over Ile-Ife, Nigeria.

Post-sunset equatorial plasma bubble (EPB) occurrences in the African sector are investigated using Global Navigation Satellite System (GNSS) radio occultation (RO) observations acquired by the FormoSat-7/Constellation Observing System for Meteorology, Ionosphere, and Climate-2 (COSMIC-2) mission. A subset of the global COSMIC-2 GNSS RO database, containing EPB events identified during the period 2023, is analyzed. The analysis is restricted to RO observations located within the African longitude sector (20°W – 40°E) and within ±20° geomagnetic latitude of the magnetic equator. EPB events are identified using complete L1-band amplitude scintillation index (S4) profiles derived from RO signal-to-noise ratio measurements. An EPB event is defined when the maximum S4 value exceeds 0.3 at F-region altitudes. Only complete RO observations, for which the sampling spatial scale is smaller than the first Fresnel zone, are considered. To focus on post-sunset ionospheric irregularities, the analysis is further restricted to observations occurring within the local time interval between 18:00 and 24:00 local time (LT). The analyzed COSMIC-2 RO observations show that EPB occurrence rates in the African sector increase rapidly after local sunset and reach a maximum during the early post-sunset period. The highest occurrence rates are observed between approximately 19:00 and 22:00 LT, after which EPB occurrences decrease toward later nighttime hours. The latitudinal distribution of detected EPBs is mainly confined within ±20° geomagnetic latitude and exhibits a near-symmetric pattern with respect to the magnetic equator. Seasonal differences in EPB occurrence are also observed, with higher occurrence rates during equinoctial periods and relatively lower occurrence rates during solstitial seasons. COSMIC-2 RO profiles associated with EPB events also show pronounced reductions in F-region electron density, accompanied by enhanced L1-band S4 values during the post-sunset period.