India, Oct. 15 -- Delhi's pollution levels rocketed into the "poor" zone for the first time in four months on Tuesday, days before Diwali, as dipping temperatures and dusty winds portended the Capital's annual winter tryst with months of toxic air, prompting authorities to roll out the first stage of the Graded Response Action (Grap) to snuff out pollutants.

The city's average 24-hour air quality index (AQI) hit 211 at 4pm on Tuesday, according to the Central Pollution Control Board's (CPCB) daily bulletin. It was Delhi's first AQI reading past 200 since 245 on June 11 and a deterioration from 189 (moderate) on Monday.

For the next three months, perhaps more, Delhi's 20 million-plus residents will inhale lungfuls of toxic air with every...