The air quality in Delhi slipped into the “poor” category early on Friday, with the Central Pollution Control Board’s Air Quality Index reading 228 at 1 am. The air quality in the national capital had been “satisfactory” before Dussehra, and fell into the “poor” category only on Thursday evening, the Hindustan Times reported.

An Air Quality Index in the range of 0-50 is considered “good”, 51-100 “satisfactory”, 101-200 “moderate”, 201-300 “poor”, 301-400 “very poor” and 401-500 “severe”.

State government officials said that the end of the monsoon season and the change in the wind pattern, as well as increasing incidents of stubble burning during the harvest season, were responsible for the dip in the air quality.

Delhi had breathed the cleanest air in five years the day after Dussehra. Data from the Central Pollution Control Board on Wednesday showed the Air Quality Index to be 173, compared to 326 last year.

Meanwhile, Delhi Chief Minister Arvind Kejriwal blamed smoke from burning stubble in neighbouring states as the chief reason for increasing pollution in the national capital. He hoped that all institutions and agencies, including the Supreme Court and the National Green Tribunal, will take steps to control it.

“Pollution in the city reduced by 25% in the earlier part of the year,” Kejriwal tweeted. “But the burning of stubble in neighbouring states in October and November is resulting in severe pollution. The smoke has started affecting Delhi’s air quality. We have been taking every possible step to check it.”

On September 25, reports said that there had been at least 117 incidents of stubble burning in Punjab in two days since the harvesting season began. The state is a neighbour of Delhi.

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