ABSTRACT
Onitsha faces severe air pollution, exposing residents to harmful levels of carbon monoxide (CO), nitrogen dioxide (NO₂), and aerosols. This study assessed Sentinel-5 Precursor (S5P) satellite data using Google Earth Engine (GEE) from 2019 to 2024, analyzing pollution trends and statistical differences across the years. The annual mean CO concentration was highest in 2024 (0.0538 mol/m²) and lowest in 2023 (0.0482 mol/m²). Monthly analysis showed that CO levels peaked in February and reached their lowest in October, reflecting seasonal variations in combustion and dispersion conditions. NO₂ concentrations peaked in 2021 (0.0000810 mol/m²) and were lowest in 2019 (0.0000686 mol/m²), monthly patterns generally exhibited maximum values in December and minimum levels during mid-year months. Aerosol levels reached their highest annual mean in 2022 (0.2309) and remained elevated in commercial areas, with monthly data indicating peak concentrations during the harmattan period (December–February) and lower levels during the rainy season. Statistical analysis confirmed varying significance across years. CO levels were significantly different between 2019 and 2020 (p < 0.05) and highly significantly different between 2022 and 2023 and between 2023 and 2024 (p < 0.01), with no significant differences between 2020 and 2022 (p > 0.05). NO₂ levels were significantly different between 2020 and 2021 (p < 0.05) and between 2022 and 2023 (p < 0.05), while other comparisons showed no significant differences (p > 0.05). Aerosol levels were highly significantly different between 2021 and 2022 (p < 0.01), with no significant differences in the other periods (p > 0.05). Pollution hotspots were found around Onitsha Main Market, Niger Bridge, and Ochanja Market, linked to traffic, industries, and open waste burning. Despite fluctuations, pollutant levels were high, posing health risks. Addressing this requires stricter emission controls, better transportation policies, and continuous air quality monitoring. Sentinel-5P and Google Earth Engine proved effective for tracking pollution trends, supporting the need for stronger environmental management in Onitsha.
