Long-term climatology and spatial trends of absorption, scattering, and total aerosol optical depths over East Africa during 2001–2019

Solar irradiance during daylight hours was calculated using the Iqbal formula, taking into account total and aerosol optical thicknesses extracted from AERONET to determine the attenuation by the atmosphere and by aerosols. Comparison of the results for sites in the equatorial zone (Singapore, San Cristobal and Mbita) and temperate zone (New Delhi, Carthage and Laguna) shows that a cloudless atmosphere weakly reduces solar irradiance in the equatorial zone, which is characterized by more regular meteorology, in comparison to the temperate zone, which is characterized by more human activity. The attenuation in the clear sky (without aerosols) seems to be independent of the region and approximately 8 ± 1% on average, except for New Delhi, for which maximum attenuation by aerosols (46%) was observed due to the high diversity of seasonal and anthropogenic sources. Attenuation by the atmosphere does not exceed 24% at sites far from industrial pollution sources (Laguna and San Cristobal). For Singapore and Carthage, where anthropogenic aerosol emissions are weak, the attenuation by the atmosphere is around 30%.

Solar irradiance attenuation by aerosols in cloudless atmosphere: equatorial and temperate examples

The emergence of COVID-19 brought with it panic and a sense of urgency causing governments to impose strict restrictions on human activities and vehicular movements. With anthropogenic emissions, especially waste management (domestic and municipal), traffic, and industrial activities, said to be a significant contributor to ambient air pollution, this study assessed the impacts of the imposed restrictions on the concentrations and size distribution of atmospheric aerosols and concentration of gaseous pollutants over West African subregion and seven major COVID-19 epicenters in the subregion. Satellite retrievals and reanalysis data sets were used to study the impact of the restrictions on Aerosol Optical Depth (AOD) and atmospheric concentrations NO2, SO2, CO, and O3. The anomalies were computed for 2020 relative to 2017-2019 (the reference years). In 2020 relative to the reference years, for area-averaged AOD levels, there was a consequential mean percentage change between -6.7% ± 21.0% and 19.2% ± 27.9% in the epicenters and -10.1% ± 15.4% over the subregion. The levels of NO2 and SO2 also reduced substantially at the epicenters, especially during the periods when the restrictions were highly enforced. However, the atmospheric levels of CO and ozone increased slightly in 2020 compared to the reference years. This study shows that "a one cap fits all" policy cannot reduced the level of air pollutants and that traffic and industrial processes are not the predominant sources of CO in major cities in the subregion. 

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1029/2022GH000597

Impacts of COVID‐19 Restrictions on Regional and Local Air Quality Across Selected West African Cities

https://doi.org/10.1016/j.sciaf.2022.e01446

An assessment of aerosol optical depth over three AERONET sites in South Africa during the year 2020

The emergence of COVID‐19 brought with it panic and a sense of urgency causing governments to impose strict restrictions on human activities and vehicular movements. With anthropogenic emissions, especially waste management (domestic and municipal), traffic, and industrial activities, said to be a significant contributor to ambient air pollution, this study assessed the impacts of the imposed restrictions on the concentrations and size distribution of atmospheric aerosols and concentration of gaseous pollutants over West African subregion and seven major COVID‐19 epicenters in the subregion. Satellite retrievals and reanalysis data sets were used to study the impact of the restrictions on Aerosol Optical Depth (AOD) and atmospheric concentrations NO2, SO2, CO, and O3. The anomalies were computed for 2020 relative to 2017–2019 (the reference years). In 2020 relative to the reference years, for area‐averaged AOD levels, there was a consequential mean percentage change between −6.7% ± 21.0% and 19.2% ± 27.9% in the epicenters and −10.1% ± 15.4% over the subregion. The levels of NO2 and SO2 also reduced substantially at the epicenters, especially during the periods when the restrictions were highly enforced. However, the atmospheric levels of CO and ozone increased slightly in 2020 compared to the reference years. This study shows that “a one cap fits all” policy cannot reduced the level of air pollutants and that traffic and industrial processes are not the predominant sources of CO in major cities in the subregion.

Rabia Said S

Papers

Multi-year analysis of aerosol optical properties at various timescales using AERONET data in tropical West Africa