Geophysical causal modelling of meteorological controls on tropospheric NO₂, CO and CH₄ over Lagos State using Sentinel-5P data

Abstract

Rapid urban expansion and associated anthropogenic pressures in Lagos State have intensified concerns about deteriorating air quality in recent decades. However, the long-term spatiotemporal behaviour of atmospheric trace gases and the extent to which meteorological conditions regulate their variability remain insufficiently understood. This study examined the spatiotemporal dynamics of CO, CH₄, and NO₂ using Sentinel-5P TROPOMI Level-3 observations spanning 2018 to 2025, and quantified their relationships with temperature, precipitation, and wind speed. Temporal trends and pollutant–meteorological linkages were assessed using the Mann–Kendall test, multiple linear regression, and Granger causality to evaluate atmospheric dynamics and meteorological controls. The results showed that mean tropospheric NO₂ column burden ranged from approximately 1.4 × 10³ to 3.4 × 10⁴ mol·m⁻², with persistently high levels observed in Apapa, Amuwo Odofin, and Alimosho LGAs, corresponding to areas of intense industrial and transport activity. CO column burden showed a similar pattern, with mean values ranging from 8.7 × 10⁵ to 6.1 × 10⁷ mol/m², while CH₄ mixing ratios varied between 1,900 and 1,960 mol/mol¹, indicating a weak upward trend in the northern and central LGAs. Regression analyses indicated that temperature exerted a strong positive influence on NO₂ (β ≈ 869.3; p < 0.001) and CO (β ≈ 5.12 × 10⁵; p < 0.001), whereas precipitation (β ≈ –0.24 to –195.6; p < 0.001) and wind speed (β ≈ –3.5 × 10³ to –2.9 × 10⁵; p < 0.05) had significant negative effects. Granger causality tests confirmed that wind speed was found to Granger-cause CO and NO₂ (p < 0.001), indicating statistically significant predictive influence rather than direct physical causation. The findings of this study suggest the need for strengthened air quality management and sustainable urban planning strategies to mitigate pollution risks and protect public health.