Air pollution

Festival of darkness

Smog tends to be worst in middle- income countries

CITY-DWELLERS are used to dirty air, but few have seen a haze like the one enveloping Delhi weeks ago. The concentration of PM2.5 (fine particles that settle in lungs) has exceeded 1,000 micrograms per cubic metre of air—100 times the limit the World Health Organisation suggests for long-run exposure. Inhaling this is as unhealthy as smoking 50 cigarettes a day. On November 1st the city closed schools and declared an emergency. It is letting cars only with odd- or even-numbered plates drive each day.

Such smog drifts over Delhi each November, after farmers burn the remnants of their rice crops to clear the land for wheat, and Hindus celebrate Diwali, a festival of lights, with a barrage of firecrackers. Even when the autumn haze subsides, air is filthy all over India—especially in the north, where the Himalayas act as a wind trap. AirVisual, a monitoring company, reckons that northern India contains 22 of the world’s 30 most toxic cities. One academic study found that of the 9.7m Indians who died in 2017, 670,000 would not have perished if the atmosphere had been clean.

The response from Indian politicians has been piecemeal. Limiting cars will help only a bit, since 75% of the pollution does not come from vehicles. Judges have tried to restrict…