We use a homogeneous 10-year record of satellite data to study recent trends in NO2 over the world's major urban agglomerations. The results indicate distinct spatial patterns in trends, with moderate but consistent reductions in NO2 throughout most developed countries and rapid increases of up to 15 % per year over many sites in Asia, Africa, and South America. We also show links between urban NO2 trends and economic as well as demographic factors, and how the latter drive regional differences.