Air quality in Delhi and its suburbs deteriorated again overnight after a marginal improvement a day ago with forecasts suggesting that a major relief is unlikely in the coming days.

The city's Air Quality Index (AQI) stood at 338 at 8 am on Monday, deteriorating from 301 at 4 pm and 290 at 7 am on Sunday.

The 24-hour average AQI, recorded at 4 pm every day, was 319 on Saturday, 405 on Friday and 419 on Thursday.

Neighbouring Ghaziabad (306), Gurugram (239), Greater Noida (288), Noida (308) and Faridabad (320) also recorded a dip in air quality.

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', 401 and 450 'severe' and above 450 'severe plus'.

The Centre on Saturday removed stringent curbs, including a ban on construction work related to linear projects and the entry of polluting trucks into Delhi in view of a dip in air pollution levels due to favourable wind speed and direction.

These measures constitute the final stage -- Stage IV -- of the Centre's air pollution control plan called the Graded Response Action Plan (GRAP).

The Commission for Air Quality Management (CAQM) in National Capital Region and Adjoining Area, a statutory body responsible for formulating strategies to combat pollution in the region, asked Delhi and NCR states to revoke all emergency measures, under which only CNG, electric and BS VI-compliant vehicles from other states are allowed to enter Delhi, with exemptions granted to those involved in essential services.

All medium and heavy goods vehicles not engaged in essential services were also banned in the capital under Stage IV of GRAP.

According to the latest CAQM order, all other curbs under stages I, II and III of GRAP, including a ban on non-essential construction work, mining, stone crushers and diesel generators will continue.