New Delhi, Delhi’s air quality remained in the ‘severe’ category as isolated showers in parts of the city made the air heavier and increased the pollution level, according to authorities.

The overall air quality index was recorded at 411, which falls in the ‘severe’ category, according to data by the Central Pollution Control Board (CPCB).

On Tuesday, the PM2.5 — particles in the air with a diameter of less than 2.5 micrometres — level was recorded at 278, while the PM10 — particles in the air with a diameter of less than 10 micrometres — was recorded at 477 in Delhi, according to the data.

Twenty one areas in Delhi recorded ‘severe’ air quality while 12 areas showed ‘very poor’ air quality, the CPCB said.

Ghaziabad, Faridabad, Greater Noida and Noida recorded ‘severe’ air quality while Gurgaon’s air quality was recorded in the ‘very poor’ category, it said.

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’.

Light showers on Tuesday hit various parts of the city which led to further deterioration of air quality, the Centre-run System of Air Quality and Weather Forecasting (SAFAR) said.

“After isolated showers in parts of Delhi, lots of moisture is introduced in the air to make it heavy and increased the holding capacity which increased the pollution level,” the SAFAR said in a report.

It also said that the stubble burning incidents have reduced significantly and now the winds are not blowing from these areas so its impact on Delhi’s air quality would be marginal.

The Supreme Court-appointed EPCA lifted the ban on the entry of heavy vehicles into Delhi on Tuesday, four days after it was imposed due to alarming pollution levels.

The EPCA — Environment Pollution (Prevention and Control) Authority — said heavy vehicles would now ply on normal timings between 11 PM and 6 AM.