Twenty-Five Years of Air Quality in Bangladesh: Trends, Seasonality, and Spatial Pollution Regimes

This study provides a comprehensive national-scale analysis of air quality in Bangladesh by examining 25 years of hourly data covering over 3.19 million records across 103 cities. It reveals that the apparent flat long-term national trend is an artifact of network expansion diluting severe pollution in hotspots like Dhaka and Narsingdi, which worsen at a rate of 1.84 AQI points per year. Furthermore, the study identifies strong, statistically significant seasonality with peaks in January and lows in July, maps a clear urban-rural gradient showing air quality improvement with distance from the capital, categorizes cities into four distinct pollution regimes via K-means clustering, and establishes that particulate matter PM2.5 and PM10 serve as the primary driver of overall AQI variation.