A thick haze engulfed the national capital as the air quality remained in the “severe” category and authorities expressed concern that light rainfall in the city may worsen the pollution levels.

The overall air quality index (AQI) was recorded at 403, which falls in the “severe” category, according to data by the Central Pollution Control Board.

An AQI between 0 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”.

Seventeen areas in Delhi recorded ‘severe’ air quality and it was ‘very poor’ in 14 areas, according to the data.

On Tuesday, the level of PM2.5 (particles in the air with a diameter of less than 2.5 micrometres) and PM10 (particles in the air with a diameter of less than 10 micrometres) in Delhi was recorded at 238 and 399 respectively.

Centre-run System of Air Quality and Weather Forecasting (SAFAR) said there is a prediction of a cloudy sky in the capital and that sometimes brings sporadic showers.

“However, such isolated showers often aggravate air pollution post event unless the spell is longer and widespread. It introduces a lot of moisture in the air and makes it heavy to hold more particulate matters,” a SAFAR report said.

The Supreme Court-appointed Environment Pollution Control Authority (EPCA) on Monday warned that if the air quality in Delhi continues to deteriorate then it would impose a complete ban on the use of non-CNG private as well as commercial vehicles.

“In the scenario that the weather remains adverse and that the current situation of air quality remains in ‘very poor’ or ‘severe’ category, then there is no option but to direct for a complete stop on the use of private and commercial vehicles other than those plying on CNG so that pollution can be contained,” EPCA Chairperson Bhure Lal had said in a letter.

The air quality in Delhi has been “severe” for the past two days. The city recorded its highest pollution level of the year a day after Diwali with an AQI of 642.