Pinhas Alpert’s team studies recent decadal trends of aerosol optical depth (AOD) over megacities around the world by using three NASA space aerosol sensors: MODIS-Terra, MODIS-Aqua and MISR. Results from these three satellites clearly show a rise in air pollution levels in the megacities of the Middle East, India and North China (see Figure 1). At the same time, Alpert et al.’s study also reveals some positive trends. Megacities in Europe, northeastern United States and South-East Asia indicate a decrease in air pollution from 2002 to 2010 (see Figure 1). These cities have taken active steps to reduce the amount of contaminants in the air. Alpert hopes that these greener cities will serve as an example to the rest of the world, inspiring those who have yet to clean up their communities to push for environmental reforms.