A Comparative Satellite-Based Study of Urban Air Pollution Trends in Sub-Saharan Africa: The Case of Asaba and Warri (2019–2024)

Abstract

Rapid urbanization and industrial activities have significantly impacted air quality in Nigeria, raising concerns about public health and environmental sustainability. While some studies have monitored air quality levels in various states and metropolitan centers, this study presents a comparative assessment of air quality in Asaba and Warri, two metropolitan centers in Delta State, focusing on nitrogen dioxide (NO₂) and aerosols over six years from 2019 to 2024. Sentinel-5 Precursor (Sentinel-5P) satellite data were used to extract pollutant concentrations through Google Earth Engine (GEE), and statistical analyses were conducted using Microsoft Excel and the Statistical Package for the Social Sciences (SPSS). The Mann-Whitney U test (MWU) was applied to assess statistical differences in pollutant levels between the two cities, and ArcGIS 10.7.1 was used for spatial visualization. The findings show that Asaba consistently recorded 25% to 38% higher NO₂ levels and aerosol concentrations between 9% and 446% higher than Warri, largely due to increased vehicular emissions, construction, and rapid urban expansion. Warri’s comparatively lower pollution levels may be attributed to coastal dispersion effects and lower traffic density in some areas. NO₂ concentrations peaked in 2021 in both cities, while aerosols fluctuated across the years, with elevated levels observed in commercial and traffic-heavy zones such as Stephen Keshi Stadium and Onitsha-Asaba Road in Asaba, and Warri Island and Inorin fishing camp in Warri. Given the health risks associated with prolonged exposure to these pollutants, the study highlights the urgent need for emission regulations, urban greening initiatives, and the adoption of cleaner energy alternatives to improve air quality in both cities.