Delhi woke on Tuesday to a dense blanket of toxic haze as its air quality deteriorated sharply, slipping into the “severe” category for the first time this season. According to the Central Pollution Control Board (CPCB), the national capital recorded a 24-hour rolling average Air Quality Index (AQI) of 421 at 7am, marking the highest pollution level of the year so far and signalling the beginning of another prolonged winter pollution crisis.

Persistent Haze and Stagnant Atmospheric Conditions

Experts attributed the alarming spike in pollutants to a combination of meteorological factors. A significant drop in wind speed, coupled with falling temperatures, created a stagnant atmospheric layer over the region. This prevented pollutants—already being continuously generated across Delhi-NCR—from dispersing. As a result, the haze that began forming on Monday morning persisted throughout the day and deepened by nightfall.

Unlike fog, which typically fluctuates based on moisture and temperature, the haze showed no signs of thinning, a clear indicator of pollutant accumulation. Visibility dropped to around 1,000 metres on Monday morning and only marginally improved to 1,500–2,000 metres by late evening. The visual density of the haze served as an unmistakable signal of deteriorating air quality long before the numbers confirmed it.

Monday’s average AQI was 362, classified as “very poor,” slightly lower than Sunday’s 370. But the trend showed consistent worsening, culminating in Tuesday’s severe-level breach.

Data Outage Raises Concerns About Pollution Monitoring

A critical disruption added to the frustration of residents and experts: pollution data went missing for nearly 10 hours on Monday due to a server issue. The national pollution bulletin, normally released around 4pm, was delayed until after 11pm. This gap left residents without official updates during what visibly appeared to be one of the most polluted days of the season.

Throughout the afternoon, the AQI remained stuck at 345, with no fresh updates until late at night. When the data finally updated at 10pm, the AQI had already climbed to 391. By midnight it surged to 398, crossing into the “severe” category shortly before 1am on Tuesday.

The last time Delhi recorded a “severe” air day was on December 23, 2024, when the AQI touched 406.

Majority of Monitoring Stations Record Dangerous Levels

CPCB’s Sameer app showed that at 7am on Tuesday, 34 out of Delhi’s 39 monitoring stations measured AQI levels in the “severe” category. Several stations recorded values at the very high end of the scale, indicating dangerous concentrations of PM2.5—fine particulate matter small enough to enter the bloodstream.

The highest readings included:

• Bawana: 462
• Wazirpur: 460
• Punjabi Bagh: 452
• Mundka: 452

Other areas such as Alipur, RK Puram, and Chandni Chowk similarly recorded AQIs well above the 400 mark, signalling severe air quality hazardous for all residents irrespective of age or health condition.

Under the national classification:

• AQI 51–100 is satisfactory
• 101–200 is moderate
• 201–300 is poor
• 301–400 is very poor
• Above 400 is severe, posing serious health risks, especially upon prolonged or repeated exposure

GRAP Stage-3 Measures Expected to Take Effect

With pollution worsening rapidly, authorities turned to the Graded Response Action Plan (GRAP), a statutory framework designed to impose progressively stricter restrictions in response to rising pollution levels.

Stage-3—activated when the AQI crosses 400—was expected to come into force following discussions by the Commission for Air Quality Management (CAQM). Under Stage-3, several mandatory measures are implemented to curb emissions and reduce pollutant load.

Key restrictions include:

• A complete ban on non-essential construction and demolition activities.
  This covers earthwork, excavation, piling, open trenching for utilities, and the operation of Ready-Mix Concrete (RMC) plants.
• Banning private BS-III petrol and BS-IV diesel four-wheelers in Delhi, Gurugram, Faridabad, Ghaziabad, and Gautam Budh Nagar.
• Prohibiting non-essential diesel-operated BS-IV medium goods vehicles.
• Banning BS-IV and lower diesel light commercial vehicles registered outside Delhi, except those transporting essential goods or providing critical services.
• Mandating hybrid learning for schools up to Class 5 in Delhi and neighbouring districts.
• Requiring staggered work timings for government offices and municipal bodies in Delhi-NCR.

These measures aim to reduce vehicular emissions, construction dust, and industrial pollutants—three major contributors to Delhi’s winter smog.

CAQM Monitoring Under Scrutiny

On Monday, the CAQM had refrained from invoking Stage-3 measures due to the pollution data outage. The delay drew criticism from environmental groups who argued that visible ground conditions were sufficient to justify immediate intervention, regardless of temporary data unavailability.

In its statement later that evening, the CAQM said it was maintaining close coordination with state agencies, pollution control boards, and urban local bodies across NCR. It added that it was “regularly reviewing sector-specific actions and compliance” to ensure pollution mitigation efforts were implemented effectively.

A Familiar Seasonal Crisis with Growing Urgency

Delhi’s severe air days have become a predictable part of the winter landscape, driven by a mix of local emissions, regional pollution sources, and unfavourable weather. Experts warn that while emergency interventions like GRAP offer temporary relief, long-term solutions demand sustained reforms in transportation, industrial emissions, waste burning, and agricultural practices across northern India.

The capital’s annual battle against pollution increasingly highlights the need for structural changes rather than reactive measures. With winter just beginning, officials anticipate that more “severe” days may occur unless weather patterns turn favourable or emissions fall significantly.

Delhi now enters another season of heightened health risk, with residents—especially children, the elderly, and those with respiratory issues—advised to stay indoors as much as possible, use air purifiers, and avoid strenuous outdoor activity until conditions improve.