Spatiotemporal dynamics of air pollution and vegetation health in a rapidly urbanizing city in northeastern Bangladesh

Air pollution poses a significant environmental concern and is recognized as the fourth leading risk factor affecting human health. Understanding the levels of air pollution and its relationships with vegetation is crucial for assessing health risks under rapid urbanization. In this study, using the extracted imagery from the Sentinel-5 and Moderate Resolution Imaging Spectroradiometer (MODIS) satellites for the period 2019-2023, five key pollutants, including ozone (O3), sulfur dioxide (SO2), carbon monoxide (CO), nitrogen dioxide (NO2), and particulate matter (PM2.5), along with normalized difference vegetation index (NDVI), were processed to analyze the monthly, seasonal, and annual patterns of these variables in a rapidly growing city in northeastern Bangladesh. Monthly and seasonal variations in the concentrations of O3, NO2, PM2.5, and CO showed significant differences, while annual variations for these pollutants were not significant. NO2 concentrations were highest during winter (85.7 μmol m-2), while the highest concentrations of CO (0.047 mol m-2), O3 (0.127 mol m-2), SO2 (137 μmol m-2), and PM2.5 (40.74 µg/m³) were observed during the pre-monsoon season. Spatial variations were also recorded for these pollutants, with higher NO2 concentrations in the eastern part and elevated SO2 and PM2.5 in the southern part. Expectedly, the highest NDVI values were recorded during the post-monsoon (0.66), while the lowest occurred during the winter (0.48). The northeastern region consistently exhibited higher vegetation greenness. NDVI showed a negative correlation with the five air pollutants studied, with significant negative correlations observed between NDVI and NO2, and between NDVI and PM2.5. Conversely, the positive correlations among the air pollutants (albeit not all were statistically significant) suggest possible shared sources or overlapping emission patterns. This study highlights the urgent necessity for targeted air quality management and urban greening initiatives to mitigate the adverse effects of air pollution on vegetation functioning and promote sustainable development in rapidly urbanizing cities.