Tropospheric Assessment of Carbon Monoxide, Nitrogen Dioxide, and Aerosols in Onitsha, Anambra State, Southeastern Nigeria – A Case Study of 2019–2024

Onitsha faces severe air pollution, exposing residents to harmful levels of carbon monoxide (CO), nitrogen dioxide (NO₂), and aerosols. This study utilized Sentinel-5 Precursor (S5P) satellite data processed through Google Earth Engine (GEE) to assess the spatiotemporal distribution and variability of these pollutants from 2019 to 2024. Statistical analyses were conducted to determine significant differences across the study years. The annual mean CO concentration was highest in 2024 (0.0538 mol/m²) and lowest in 2023 (0.0482 mol/m²). NO₂ levels peaked in 2021 (0.0000810 mol/m²) and were lowest in 2019 (0.0000686 mol/m²), while aerosols reached their highest mean concentration in 2022 (0.2309) and remained elevated in commercial areas. Statistical analysis reviewed significant variations across years. CO levels showed significant differences between 2019 and 2020 (p < 0.05) and highly significant differences 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. Despite fluctuations, pollutant levels remain high, posing serious health risks. Addressing this requires stricter emission controls, better transportation policies, and continuous air quality monitoring to safeguard public health and the environment.