The Supreme Court today reprimanded authorities for delaying the implementation of stringent measures under the Graded Response Action Plan (GRAP), as Delhi's air quality plunged to the'severe-plus' category this morning.

The Supreme Court also directed the Commission for Air Quality Management (CAQM) in the National Capital Region and the Delhi government to ensure that restrictions under Stage 4 of the Graded Response Action Plan (GRAP)—triggered when the Air Quality Index (AQI) exceeds 400—are not eased without its approval, even if the AQI falls below 300.

A bench comprising Justice AS Oka and Justice AG Masih questioned the authorities over the three-day delay in implementing Stage 3 of the Graded Response Action Plan (GRAP) after the Air Quality Index (AQI) crossed the 300 mark. Responding to the Centre's counsel, who claimed they were monitoring if the AQI would dip, the court remarked, "Once it reaches, it has to be invoked... How can the applicability of Stage 3 be delayed? How can you wait for three days?"

The court then said, "We are making it very clear that you will not go below Stage 4 without our permission now, even if AQI goes below 300; that is the order we are proposing." The matter will be taken up again later in the day.

The Commission for Air Quality Management (CAQM) implements a four-tier Graded Response Action Plan (GRAP) to combat Delhi’s severe air pollution. GRAP 1 is activated when the AQI falls into the 'poor' category, enforcing measures such as periodic water sprinkling on roads, banning open burning of waste, and restricting diesel generator usage. 

When the AQI exceeds 300, GRAP 2 is invoked, intensifying measures like daily road sprinkling, ensuring uninterrupted power supply to minimize generator use, hiking parking fees to discourage private vehicle use, and enhancing CNG and electric bus services, as well as Metro operations.

At the next level, GRAP 3 comes into effect when the AQI crosses 400. Under this stage, polluting vehicles are banned in Delhi and the NCR, governments may decide on online classes for primary students, and activities such as mining, stone crushing, and construction or demolition are prohibited.

GRAP 4, currently in effect, is implemented when the AQI exceeds 450. Under this stage, commercial vehicles registered outside Delhi are barred from entering the capital unless they are electric vehicles (EVs), CNG-powered, or comply with BS-VI emission norms. Authorities can also decide on suspending physical classes for senior students as part of the measures.