India, Nov. 9 -- Many of the city's air quality stations going dark on Diwali night does not help in answering this question consistently. And the warmer night perhaps helped despite firecrackers being used well beyond prescribed limits. The air, despite relatively favourable weather, is still close to the 'severe category' - the threshold for pollution reaching its most harmful levels.

A consistent comparison of Diwali air pollution requires comparable data over time. More than half the air quality stations in the national Capital stopped reporting air quality data around midnight. This happened even as the stations that continued to report data found the air "severe" or with the Air Quality Index (AQI) above 400. Around 80% of function...