The Delhi ‘gas chamber’: smog, air pollution and the health emergency of November 2017

The thick smog that blanketed India's capital, New Delhi, in early November 2017 saw air quality index values peak above 1000 – a figure in excess of three times the threshold value for ‘hazardous’ conditions. A public health emergency was declared. Delhi's smog was the result of an existing ambient urban air‐pollution problem, significantly worsened by smoke blowing in from numerous agricultural fires burning across neighbouring Punjab and Haryana states. Post‐summer monsoon regional air‐flow patterns, decreasing autumn temperatures, high‐pressure stability, temperature inversion and light local winds helped to produce climatic conditions that were conducive to smog build‐up and subsequently prevented it from readily dispersing. Well‐intentioned measures introduced by the authorities saw only partial improvement in city air quality after three weeks. To reduce the severity of future smog hazards, a region‐wide agreement to restrict stubble burning during late autumn across northwest India will be needed.