Evaluation of spatial distribution and temporal trend of nitrogen dioxide (NO2) pollution using Sentinel-5P satellite imagery over Afghanistan based on Google Earth Engine

Air pollution is a significant crisis globally, including in Afghanistan's major cities, driven by industrialization, population growth, and increased urban traffic. Nitrogen dioxide (NO2) is one of the main air quality pollutants worldwide, that not only harms human health but also affects vegetation and contributes to global climate change. As a result, comprehensive monitoring of this pollutant is essential for informed decision-making to address these crises. The TROPOMI sensor on the Sentinel-5P satellite, provides images across a wide range of spectral bands making it a powerful tool for air pollution monitoring. Using the TROPOMI sensor and the Google Earth Engine (GEE) platform, this study investigates the monthly, seasonal, and yearly spatiotemporal changes of NO2 over Afghanistan from 2019 to 2023. The TROPOMI product was also validated using a surface NO2 data, which showed a significant connection ranging from (R = 0.66 to 0.99) throughout the four seasons. According to the spatial study, NO2 is mainly concentrated in large cities like Kabul, Nangarhar, Balkh, Herat, and Kandahar and is widely dispersed over the northern, eastern, southern, and western regions of Afghanistan. The most polluted seasons are spring and summer, with the greatest NO2 levels found in May, June, and July. Temporal trend analysis shows that while there were minor increases in Herat and Balkh, NO2 levels showed a downward trend in Kabul, Nangarhar, and Kandahar. Policymakers and government officials will benefit from the study's findings in developing focused plans to effectively address air pollution and reduce NO2 emissions.