Delhi's toxic winter air is back - is the Indian capital prepared for pollution?

"If we want to reduce pollution, we need to set targets for every sector - including power generation, industry and transport - not just vehicle entry, construction and stubble burning," says Manoj Kumar, an analyst at the Centre for Research on Energy and Clean Air.

"We know how much each sector and each state contributes to pollution. We can set targets to reduce emissions from each of them over the next five years."

Bosu points out that an issue which does not get enough attention is secondary pollutants - when gases in the air react with sunlight, water vapour and other substances to form harmful particles that contribute to pollution.