CITY-DWELLERS are used to dirty air, but few have seen a haze like the one enveloping Delhi this week. 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.
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