Aerosols such as smoke or dust suspended in the lower layers of the atmosphere can either heat up the planet by trapping solar radiation, or cool it by reflecting sunlight back into space. Little is known, however, about how much aerosols that are present much higher up — above the clouds — contribute to this warming.
An IIT Bombay study using satellite data shows rising greenhouse gas levels over Delhi and Mumbai and also identifies emission hotspots in these cities.