This week, Delhi residents are battling toxic air once again.

On Dec. 23 and Dec. 24, as the weather got chillier and fog engulfed the city, India’s national capital reportedly experienced its most polluted days of the year, with the air quality index at an “emergency” level. Since then, things have just barely improved as high levels of fine particulate matter have kept the air in most parts of the city “hazardous” even today (Dec. 26). At this level, residents are at risk of serious health effects and are encouraged to avoid all outdoor activities, an instruction that is especially difficult for those who have to work outside.

Delhi’s air pollution makes the headlines every year during the winter months, usually, after farmers begin burning crop stubble in neighbouring states such as Punjab and Haryana. The trouble with Delhi is its geography, which ensures that pollutants carried from other states in the wind are trapped in the air above it. In this context, the addition of vehicular emissions and other regular polluting activities turns the city’s air into an especially toxic mess…