Over the past decade, research has shown a dramatic drop in the amount of household air pollution coming from inside Delhi. Since 2007, the contribution of household air pollution to ambient air pollution has fallen around 40%-50%. The improvement is due in large part to people switching from traditional, solid fuel-burning chulas to cleaner, more efficient cooking fuels such as LPG and electricity, which are used by more than 80% of households and commercial entities.
Despite this progress, however, the levels of ambient air pollution within Delhi have continued to worsen during the same period. Multiple sources contribute to this increase, according to data from UrbanEmissions.info, including industry, transport, dust, waste burning, seasonal crop burning (outside Delhi), power plants, and diesel generator sets. Yet one often overlooked source is coming from the homes of people living beyond Delhi's city limits. That source is cooking and space heating.