New dELHI, Oct. 31 -- 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. 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. Aft...