Delhi’s air quality fell into the "very poor" category this week, days before the Hindu festival of Diwali was expected to make it worse.

The Central Pollution Control Board classes readings of 301 to 400 as "very poor" and beyond 400 as "severe".

The deterioration in air quality came after the Indian capital saw the lowest average AQI for October in eight years, at 166, and north-westerly winds carrying smoke from crop burning in neighbouring states returned after a storm.

The Commission for Air Quality Management, which coordinates pollution control across the National Capital Region, invokes Stage II of the Graded Response Action Plan on Monday. Stage II involves the use of measures such as more mechanical sweeping and water sprinkling to control road dust, higher parking charges to discourage private vehicle use, restrictions on the use of coal and firewood in open eateries and restaurants, stricter rules on diesel generators, and more inspections of construction and demolition sites.…