Shocked by the sudden Delhi haze, smog and whatnot? This is the reason

Delhi’s sudden pollution spike was driven mainly by incoming smoke from evening farm fires in Punjab and Haryana. Stagnant weather helped pollution build up, but HT’s comparison found that weather alone could not explain the sharp deterioration. The source region and wind direction were crucial.

PM2.5 averaged 194 micrograms per cubic metre overnight on November 1, more than three times India’s safe limit. Unlike earlier dates, pollution did not clear by mid-afternoon. It nearly doubled within three hours around midday on October 31, showing that a fresh load of dirty air had arrived from outside Delhi.

Transport-level winds on October 31 and November 1 came from the northwest fire belt. A three-day trajectory showed the arriving air had passed over Punjab and Haryana fires. The AQI reached 324 by Monday, prompting Stage-II GRAP measures across the NCR, including dust controls and more road sweeping.

The Air Quality Index, or AQI, is a single number used to communicate how polluted the air is and the potential health concern. Higher values indicate worse air. In the article’s classification, AQI between 301 and 400 is “very poor,” the range that triggered Stage-II GRAP across the NCR.

Delhi’s index climbed from 117 on Saturday to 261 on Sunday, then reached 324 by Monday’s 4 PM bulletin. That crossed the 300 threshold for the first time that season. The pollution was especially concerning because fine particles formed a large share of the air and remained elevated instead of clearing during the afternoon.

People with respiratory problems were advised to avoid outdoor activity during heavy pollution, particularly early morning and at night. Masks were recommended. Those with chronic conditions were told to continue prescribed medicines and seek medical advice if symptoms worsened.

Fine particles, especially PM2.5, are very small airborne pollutants that can travel deep into the respiratory system. Their share helps indicate the type of pollution present. HT found that fine particles made up nearly 60% of total particulate matter on the night of November 1, pointing more strongly to smoke than coarse road dust.

Delhi’s PM2.5 averaged 194 micrograms per cubic metre between 10 PM and 6 AM. India’s safe limit is 60 micrograms per cubic metre, so the measured level was more than three times higher. On October 18 and 28, the corresponding averages were 68 and 127.

The unusually high fine-particle share matched the movement of smoke from farm fires. High humidity above 90% may also have helped convert gases into fine particles. Together, the particle composition, weather, and wind direction linked the pollution episode to incoming smoke rather than local dust alone.

Winds can move pollution across state borders, so Delhi’s air quality depends partly on conditions outside the capital. During this episode, transport-level winds in the afternoon came directly from the northwest fire belt. That direction aligned with active farm fires in Punjab and Haryana.

HT used Safdarjung balloon readings and global weather models to trace the air’s three-day path. The air reaching Delhi on November 1 had spent most of that time over Punjab and Haryana, passing over dozens of fires. On October 28, winds arrived from the south and east and avoided the fire belt; Delhi’s air was cleaner.

The contrast showed why the timing and direction of winds mattered. Overnight pollution normally dissipates as sunlight warms the ground, but it did not clear on November 1. Smoke arriving from neighbouring states added a new pollution load, helping push Delhi’s AQI to 324.

The usual fire-count measure relies on a NASA satellite pass over Punjab at about 1:30 PM. That schedule can miss fires that begin later in the day. HT found that crop-burning patterns had shifted strongly toward evening, when the standard snapshot is no longer observing the relevant conditions.

A 2025 iFOREST report found that more than 90% of large Punjab fires in 2024 and 2025 were lit after 3 PM. The figure was only 3% in 2021. India’s geostationary INSAT-3DS satellite scans continuously, so it captured evening fire counts rising from 17 on October 29 to 90 on November 1.

INSAT-3DS detects only larger fires, meaning the actual number of burning fields was likely higher. Better monitoring of the full day matters because late fires can produce smoke that reaches Delhi overnight or the next day. Standard afternoon snapshots may therefore understate the pollution threat.

Crop-residue, or stubble, fires are fires set to remove the straw, stalks, and other plant material left after crops are harvested. They are especially relevant here because smoke from fields in Punjab and Haryana was identified as the main outside source behind Delhi’s pollution spike.

Burning is commonly used because it clears a field quickly and at low direct cost, leaving it ready for the next crop. The article does not give a specific reason from individual farmers, but it documents the scale and timing of the fires. More than 90% of large Punjab fires in 2024 and 2025 were lit after 3 PM.

That timing matters beyond the fields themselves. Evening fires can release smoke when winds later carry it toward Delhi. INSAT-3DS recorded evening fire counts increasing from 17 on October 29 to 90 on November 1. Because it detects only large fires, the real number was likely higher.

A temperature inversion occurs when warmer air sits above cooler air near the ground. This arrangement limits vertical mixing, so pollution remains concentrated where people breathe. Still nighttime air has a similar effect. The article notes that dawn inversion strength and night stillness were as severe, or worse, on October 18 and 28, yet Delhi was cleaner then.

Humidity adds another mechanism. Humidity above 90% on October 31 and November 1 may have helped gases convert into fine particles. Normally, sunlight warms the ground and trapped overnight pollution falls by mid-afternoon. On November 1, PM2.5 did not decline; instead, it nearly doubled in three hours around midday.

That difference showed that local weather was not the whole explanation. Incoming smoke from Punjab and Haryana arrived while Delhi’s atmosphere was already capable of trapping pollution. The combination produced unusually dirty afternoon air and helped drive the AQI to 324.