Air pollution increases during the winter months because cold air usually sinks and warm air rises. The warmer air acts like a dome trapping the cooler air below with the pollutants from several sources. This explains the winter smog in cities.

51% of the pollution is caused by industrial pollution, 27 % by vehicles, 17% by crop burning and 5% by other sources.

Twenty-two of the 30 most polluted cities in the world are in India, and almost 99% of Indians breathe air that breaches the WHO’s defined safety limits.

Long-term exposure to unhealthy air increases the risk of respiratory disease. India has one of the highest rates of child mortality, in part due to both toxic air and polluted water.

India has 804 manual and 286 real-time air quality monitoring stations, translating to a density of ~0.8 monitors per million people, well below that of China or the US. Most monitors are located in urban centres, while rural areas lack real-time monitoring.