The air quality in the national capital was in the 'severe' category on Tuesday morning with an AQI of 427 while the minimum temperature was 5.9 degrees Celsius, two notches below normal.

Out of 35 monitoring stations, 28 recorded air quality in the 'severe' category while some breached the 450 mark, classified as 'severe plus.' The remaining seven stations recorded air quality in the 'very poor' category, according to the Sameer app, which provides hourly data from the Central Pollution Control Board.

An AQI of 400 or higher is deemed "severe" and it can have an adverse effect on both healthy individuals and people with medical conditions.

The weather department said, "Mainly calm winds prevailed over Delhi during the past 24 hours, bringing down visibility from 800 meters in shallow fog at Palam on Monday to 350 meters in moderate fog at Safdarjung on Tuesday morning." It added that moderate fog conditions (visibility between 200m and 500m) are likely to persist in Delhi over the next two days due to the expected prevalence of calm or easterly surface winds.

Humidity was 97 per cent at 8:30 am.

The maximum and minimum temperatures are expected to settle at 24 degrees Celsius and 5 degrees Celsius, respectively.

The Centre's air quality panel for Delhi-NCR on Monday imposed the strictest Stage 4 curbs under the winter air pollution control plan, including a ban on all construction activities, as the region's air quality deteriorated to 'severe' due to unfavourable weather conditions.

Stage 4 curbs under the Graded Response Action Plan (GRAP) for winters also include a ban on the entry of polluting trucks carrying non-essential goods into Delhi and mandatory shifting of school classes, except those for X and XII, to hybrid mode.

The decision to impose Stage 4 curbs came just hours after the Commission for Air Quality Management (CAQM) implemented restrictive measures under GRAP Stage 3, following Delhi's AQI breaching the 350 mark in the afternoon.

During winters, Delhi enforces restrictions under GRAP, which categorises air quality into four stages -- Stage I (Poor, AQI 201-300), Stage II (Very Poor, AQI 301-400), Stage III (Severe, AQI 401-450), and Stage IV (Severe Plus, AQI above 450).

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