Tracking the Path to Cleaner Cities using Global Urban NO₂ Monitoring from Space

Tracking air pollution is essential for evaluating the effectiveness of urban air-quality and emission-control policies and their impact on public health. Unlike previous satellite-based urban NO₂ studies that typically rely on linear trends, aggregated data, and limited meteorological correction, we use high-resolution TROPOMI observations with an AirGAM framework to estimate meteorology-adjusted, non-linear NO₂ TVCD trends across 5,435 cities worldwide (2019–2024). Daily satellite observations, together with ERA5 meteorology, are used to remove weather and seasonal effects so that trends primarily reflect changes in emissions. 1,400 cities had significant trends, with 79% showing declines, indicating an overall global drop in urban NO₂ TVCD. East Asia, particularly China (99% of cities with significant trend), and Europe (95%) led the global reductions. Cities in the USA with significant trends (n = 14) also experienced a decline. NO₂ TVCD levels increased most sharply in the cities of the Middle East, Central, and South Asia. The most populated examples are Tehran (3.1% yr-1 [95% CI: 0.7–5.5]) and Cairo (1.4% yr-1 [0.1–2.6]).