Spatio-Temporal Dynamics of Tropospheric NO₂ over Dhaka Division (2019–2024), Bangladesh

Air pollution poses a significant public health and environmental challenge in Bangladesh, particularly in Dhaka Division, where limited monitoring infrastructure highlights a critical research gap in understanding the spatio-temporal dynamics of tropospheric nitrogen dioxide (NO₂). This study addresses this gap by analyzing daily NO₂ concentrations in Dhaka Division from 2019 to 2024 using high-resolution Sentinel-5P TROPOMI satellite data, validated with ground-based observations from the Department of Environment's Continuous Air Monitoring Stations (CAMS), and integrated with meteorological data via Principal Component Analysis (PCA). Results reveal a distinct weekly cycle, with NO₂ levels peaking on Sundays (up to 2.38 × 10¹⁵ molecules/cm²) and declining on Fridays (2.15 × 10¹⁵ molecules/cm²), alongside seasonal variations with winter maxima (up to 10.60 × 10¹⁵ molecules/cm² in January) and monsoon minima (0.32 × 10¹⁵ molecules/cm² in July), driven by meteorological conditions. The Mann-Kendall test and Sen's slope estimator indicate significant upward trends (up to 0.32 × 10¹⁵ molecules/cm² per year) in urban-industrial areas, such as Narayanganj, with peak annual concentrations reaching nearly 7 × 10¹⁵ molecules/cm² during 2021–2022, likely due to post-COVID activity surges. Validation yields moderate Pearson correlations (R = 0.20–0.32) between satellite and ground data, effectively capturing seasonal trends. Meanwhile, PCA explains 89.23% of the variance, highlighting the influence of temperature and surface pressure on NO₂ dynamics. Compared to prior studies that were limited to the COVID-19 period or relied on single data sources, this research provides a comprehensive and integrated analysis. These findings underscore the need for enhanced monitoring and informing policies to mitigate urban air pollution in vulnerable regions, such as Dhaka Division.