The Air Quality Index in Delhi and its surrounding areas remained in "severe" category on Tuesday with PM 2.5 levels at 421 in the capital and PM 2.5 at 529 in Gurugram, according to the System of Air Quality and Weather Forecasting And Research (SAFAR).

The AQI at Mathura road, Pusa, Delhi University, Lodhi Road, IIT Delhi and Ayanagar was recorded at 488, 425, 410, 410, 402 and 416, all in the "severe category", on Tuesday.

The AQI in Noida reached 458 under the "severe" category.

An AQI between zero and 50 is considered "good", 51 and 100 "satisfactory", 101 and 200 "moderate", 201 and 300 "poor", 301 and 400 "very poor", and 401 and 500 "severe".

According to Central Pollution Control Board data, the national capital was the most polluted city in India in 2022 with PM 2.5 levels more than double the safe limit and the third highest average PM10 concentration.

PM2.5 is tiny particulate matter that can enter the lungs and bloodstream and it is less than 2.5 microns in diameter.

"With respect to PM 2.5 level among the top polluted cities, Delhi with 99.71 micrograms per cubic metre had ranked first, neighbouring Faridabad in Haryana with 95.64 micrograms per cubic metre) ranked second and Ghaziabad's PM 2.5 at 91.25 micrograms per cubic metre ranked third," CPCB data stated.

The air quality had suddenly and unexpectedly deteriorated owing to dense foggy conditions without much sunlight and very low temperatures, coupled with calm winds and stable atmospheric conditions, said experts

With the air quality worsening, the Delhi government on Tuesday imposed a temporary ban on using BS-III petrol and BS-IV diesel four-wheelers in the national capital.

According to the order released by the Delhi Transport Department, the Sub-Committee for operationalisation of the revised GRAP has reviewed the air quality scenario as well as the forecasts for meteorological conditions and Air Quality Index in Delhi.

"As per directions as provided under Stage III of the revised GRAP and under Section 115 of Motor Vehicle Act, 1988, it is hereby ordered that there shall be restrictions to ply BS-III, Petrol and BS-IV, Diesel LMVS (4 wheelers) in NCT of Delhi, with immediate effect, till dated 12:02:23 or till downward revision in GRAP stage, whichever is earlier (except for vehicles deployed in emergency services, police vehicles and government vehicles used for Enforcement)," stated the order.

It said that any such vehicles found plying on roads will be prosecuted under section 194(1) of Motor Vehicle Act, 1988 which provides a fine of Rs 20,000. (SJ/IANS)