Delhi AQI discrepancy: CPCB records 483, private monitors report over 1,000

Delhi woke up to a thick blanket of toxic smog on Monday, November 9, with air quality deteriorating to the ‘severe’ category hours after Diwali celebrations continued late into the night. The Central Pollution Control Board (CPCB) recorded an overall Air Quality Index (AQI) of 483 at 8.10 am, while private monitoring organisations reported readings exceeding 1,000 in parts of the capital.

At least 15 monitoring stations across Delhi recorded AQI levels above 400, as visibility dropped sharply and residents struggled to move through the dense haze. The deterioration came despite Stage III of the Graded Response Action Plan (GRAP) being in force across the National Capital Region (NCR).

The CPCB’s citywide reading was 483, but IQAir, a Swiss company specialising in protection against airborne pollutants, reported an AQI of more than 1,000 in Shahdara and south Delhi’s Defence Colony. Such figures from private platforms should be read with caution, as they may use different measurement systems and AQI scales.

Several neighbourhoods record severe pollution

Station-level readings showed that large parts of Delhi were experiencing severe air pollution. Vivek Vihar recorded an AQI of 445, although separate hourly CPCB logs put it at 437. Burari Crossing registered 441, while Jahangirpuri recorded readings ranging between 433 and 442.

Rohini’s AQI fluctuated between 430 and 438, while Delhi Technological University (DTU) recorded readings between 430 and 434. Other locations in the severe category included North Campus at 433, Bawana at 427, Ghazipur at 418, Mundka at 417, Punjabi Bagh at 408 to 409 and the National Institute of Health (NIH) station at Narela at 407.

Some monitoring stations reported levels just below the severe threshold. The Central Road Research Institute (CRRI) on Mathura Road recorded an AQI of 396, while the Dr Karni Singh Shooting Range registered 361. Najafgarh recorded 340, placing it in the ‘very poor’ category.

RK Puram and Nehru Nagar, near south Delhi’s Lajpat Nagar, were among the worst-affected locations until 9 pm. The real-time monitoring system initially showed a sharp rise in pollution, but the Delhi Pollution Control Committee’s (DPCC) website reportedly stopped displaying live readings from several stations for a few hours, news agency IANS reported. The interruption is believed to have affected the availability of monitoring data during the peak pollution period.

AQI readings and actual pollution levels

The CPCB’s AQI is calculated on a scale of 0 to 500. However, readings exceeding the concentration corresponding to 500 are generally displayed as ‘500’ or ‘500+’. This means that even if PM2.5 concentrations rise substantially beyond the severe threshold, the public-facing AQI may not reflect the extent of that increase.

AQI is an indicator of air quality based on the concentration of pollutants, not a direct measurement of the amount of particulate matter in the air. Consequently, the index may remain capped at 500 even as actual PM2.5 concentrations continue to climb.

The CPCB classifies an AQI of 0 to 50 as ‘good’, 51 to 100 as ‘satisfactory’, 101 to 200 as ‘moderate’, 201 to 300 as ‘poor’, 301 to 400 as ‘very poor’ and 401 to 500 as ‘severe’.

Visibility drops as smog blankets roads and landmarks

The pollution spike had a visible impact across the capital. At the busy ITO intersection, where the CPCB recorded an AQI of 407, commuters and pedestrians struggled to breathe through the dense smog. Several people complained of persistent headaches and burning eyes.

A thick grey haze also obscured the Akshardham temple from the adjoining flyover, just a few kilometres away. An NDTV reporter at the location said visibility had deteriorated to the extent that the temple, which could previously be seen clearly from the flyover, was hidden behind a layer of haze.

The Air Quality Early Warning System for Delhi had forecast further deterioration during the day, citing unfavourable meteorological conditions.

Drivers along the Delhi-Noida border and in north Delhi’s Inderlok switched on their headlights during the morning hours to navigate through the poor visibility.

Severe pollution despite GRAP Stage III restrictions

The post-Diwali deterioration came despite the Commission for Air Quality Management (CAQM) invoking Stage III of GRAP on November 6, three days before Diwali. The decision was based on pollution and meteorological forecasts issued by the India Meteorological Department (IMD) and the Indian Institute of Tropical Meteorology (IITM).

The four-stage emergency framework is managed by the CAQM in coordination with the CPCB and the governments of Delhi, Haryana, Uttar Pradesh and Rajasthan. It introduces progressively stricter restrictions as air quality deteriorates across the NCR.

Stage III includes a halt to non-essential construction and demolition activities, tighter restrictions on certain vehicles and hybrid classes for primary school students. It also builds on measures under the earlier stages, including dust-control measures and restrictions on polluting activities.

The CAQM’s decision to activate Stage III ahead of Diwali was a preventive measure intended to limit further deterioration. The restrictions, however, did not prevent pollution levels from entering the severe category after the festival.

Pollution levels rise across northern India

The deterioration was not confined to Delhi. Several parts of Lucknow in Uttar Pradesh were covered in a thick layer of smog on Monday morning, while haze was reported in Mumbai’s Kalanagar and Bandra areas.

Monitoring stations in Mumbai recorded an AQI of 264 at Kherwadi-Bandra East, 226 at Sewri and 221 at Ghatkopar, among other locations.

Delhi’s pollution crisis also comes against a backdrop of persistently poor air quality in the days leading up to Diwali. The city’s 24-hour average AQI stood at 382 on November 6, before improving to 369 on November 7 and recording 376 on Diwali, November 8. These daily averages are separate from the sharp hourly and station-level readings recorded during the post-Diwali pollution spike.

The Air Quality Early Warning System has warned that unfavourable weather, including low wind speeds and poor ventilation, could prevent pollutants from dispersing and keep air quality in the very poor or severe range over the following days. Firecracker emissions have added to the existing pollution burden from vehicles, industrial activity, construction dust and crop-residue burning in neighbouring states.

The latest readings underline the difference between activating emergency restrictions and achieving a sustained reduction in pollution. While GRAP Stage III remains in force, the scale of the post-Diwali spike has raised fresh concerns over the effectiveness of pollution-control measures and the ability of authorities to prevent hazardous air conditions in the capital.