By mid- to late November every year, a pall of noxious air settles over the entire Indo-Gangetic Plain, stretching from eastern Pakistan to Bangladesh. This year, the haze was visible in satellite images and disrupted daily life in large cities such as Lahore and Delhi, leading to school closures and weekend curfews reminiscent of COVID-19 lockdowns.

The causes of this phenomenon are well known. Pollution levels typically begin to surge during the autumn festival of Diwali because of the widespread use of fireworks. The situation worsens as farmers burn leftover rice-paddy stubble to prepare fields for the winter (rabi) crop, following the harvest of the summer (kharif) crop. These seasonal factors, combined with background pollution from vehicular and industrial sources, create a public-health emergency in the region every year.

On cue, on 18 November this year, Delhi’s Air Quality Index soared to 1,700 — far exceeding the safe limit of 50 set by the World Health Organization (WHO). Lahore in Pakistan had recorded a value of 1,100 a few days earlier. Because the Indo-Gangetic Plain is one of the most densely populated regions globally, the number of people affected would be in the millions — making the north Indian pollution plume one of the world’s biggest public-health challenges. Yet it is solvable.

A comprehensive, year-round mitigation plan is required. Delhi’s case is illustrative of the challenges confronting the entire region. In 2019–22, the city’s annual average concentration of PM2.5 — harmful microscopic particles that can penetrate deep into the lungs and bloodstream — was about 20 times higher than the WHO’s clean air standard1. Most people in South Asia breathe polluted air throughout the year, resulting in a reduction in average life expectancy of about five years.