India, Nov. 2 -- Smoke from farm fires in Punjab and Haryana drove the sharp rise in Delhi's pollution on Sunday, which pushed the air into the "very poor" range on Monday, an HT analysis of air-quality, weather and satellite data has found. Most of the fires were lit in the evening, after the NASA satellite whose count is the standard measure of stubble burning had passed over the region.

Delhi's air quality index, which runs from 0 to 500, rose from 117 on Saturday to 261 on Sunday. By Monday morning the Central Pollution Control Board's (CPCB) hourly reading had crossed 300, the threshold for "very poor" air. Monday's 4pm bulletin put the index at 324, the season's first very poor reading. The last very poor reading this year was on F...