The Supreme Court on Monday questioned the Delhi government over delay in implementation of stricter anti-pollution measures under GRAP-4, and said it will not allow scaling down of the preventive measures without its prior permission.

A bench of Justices Abhay S Oka and Augustine George Masih pointed out that there was a delay in implementation of preventive measures under stage 4 of the Graded Response Action Plan (GRAP) even after the Air Quality Index (AQI) touched alarming levels in the national capital.

At the outset, the counsel for the Delhi government informed the bench that stage 4 of GRAP has been implemented from Monday and heavy vehicles have been banned from entering the national capital.

“The moment the AQI reaches between 300 and 400, stage 4 has to be invoked. How can you take risk in these matters by delaying applicability of stage 4 of GRAP,” the bench told the counsel.

It told the state government that the court wants to know what steps it has taken to curb the alarming rise of pollution level.

"We won't allow scaling down of preventive measures under stage 4 even if AQI goes below 450. Stage 4 will continue till court permits," the bench said, adding it will hear the matter in detail at the end of the day's work.

On Sunday, the CAQM announced stricter pollution control measures for the Delhi-NCR under GRAP-4, effective from 8 am on Monday, including a ban on truck entry and a temporary halt on construction at public projects.

The Commission for Air Quality Management (CAQM) issued the order as Delhi's Air Quality Index (AQI) worsened, reaching 441 at 4 pm and rising to 457 by 7 pm due to unfavourable weather conditions.

According to the order, no trucks would be allowed into Delhi except for those carrying essential items or using clean fuel (LNG/CNG/BS-VI diesel/electric).

Non-essential light commercial vehicles registered outside Delhi will also be prohibited, except for EVs and CNG and BS-VI diesel ones.

On November 14, the top court had agreed to urgently list the plea after it was told that Delhi should not become the most polluted city in the world due to the rising pollution.

It had earlier said the right to live in a pollution-free atmosphere was a fundamental right of every citizen, protected by Article 21 of the Constitution.

The apex court is hearing a plea seeking directions to curb air pollution in the national capital and adjoining areas.