SPIKE IN DELHI AQI PUTS DATA UNDER A CLOUD

Between 4pm on October 29 and 4pm on October 30, Delhi's air quality index or AQI spiked by almost 100 points, from 279 to 373, pointing to either a sharp increase in pollution or an underreporting of the index on October 29.

- Abhishek Jha

With the index, which is a rolling 24-hour average crossing 370 early in the morning of October 30, the air pollution between 4pm on Wednesday and 10 am on Thursday would have had to be deep in the red — the kind of spike that is physically not probable.

A Hindustan Times analysis of AQI readings over the past three days, and satellite imagery modelled estimates of pollution suggest that Thursday's reading could be a result of both — a spike over the past 24 hours, and previous underreporting. After all, Wednesday (October 29), looked visibly like a 350-plus day, as longtime sufferers in the Capital can vouch.

AQI readings on Oct 28, 29 and 30 point to this There has been a visibly dense haze in Delhi for the past three-four days. Anecdotally speaking, the official AQI numbers for October 28 and 29 the 24-hour averages at 4pm were 294 and 279 seemed to underestimate the ambient pollution. On October 30, the haze was largely similar to the previous two days, but the AQI reading increased to 373 in the Central Pollution Control Board bulletin, a jump of almost hundred points. What really led to this?

Not a calculation error