As Delhi’s air quality plunged to the ‘severe-plus’ category this morning, the Supreme Court today pulled up authorities over the delay in implementing tough restrictions under the Graded Response Action Plan (GRAP) to tackle the capital’s bad air days.

The court also told the Commission for Air Quality Management (CAQM) in the national capital region and the Delhi government that restrictions under Stage 4 of GRAP — implemented after Air Quality Index crosses the 400 mark — must not be relaxed without its permission even if AQI drops below 300.

The bench of Justice AS Oka and Justice AG Masih asked the authorities why GRAP 3 was implemented three days after the AQI crossed the 300 mark. When the Centre’s counsel replied that they were tracking whether the AQI dips, the court said, “Once it reaches, it has to be invoked… how can the applicability of stage 3 be delayed anyhow… 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.

CAQM has a four-step Graded Action Response Plan to tackle Delhi’s bad air days. GRAP 1 is invoked when the AQI is in poor category. Under this category, water is periodically sprinkled on roads, open burning of waste is banned and use of diesel generations is restricted. Under GRAP 2, enforced when AQI crosses the 300 mark, water is sprinkled on roads daily, uninterrupted power supply is ensured so that use of generators can be avoided, parking charges are hiked to discourage private transport and service of CNG and electric buses and Metro are stepped up.

The next stage of curbs, GRAP 3, is enforced when AQI crossed 400. Polluting vehicles in Delhi and other cities in the National Capital Region are banned and governments may take a call on online classes for primary students. Mining, stone-crushing and construction/demolition activities are prohibited under GRAP 3.

GRAP 4, which is currently in force, kicks in when AQI crossed the 450 mark. Commercial vehicles registered outside Delhi are banned from entering the capital unless they are EVs, CNG or they conform to BS-VI norms. Decisions can also be taken on discontinuing physical classes for senior classes too.