Delhi's air quality deteriorated sharply on Monday morning, entering the very poor category for the first time this season as a thick layer of smog enveloped the national capital. The city's Air Quality Index touched 307 at 7.05 am, according to real-time data from the Central Pollution Control Board, and rose further to 310 by 8 am.
The deterioration comes just a week before Diwali, when firecracker emissions are expected to add to the pollution load, and follows a brief spell of relief brought by rain late last week.
The slide in air quality was swift. Delhi had recorded a 24-hour average AQI of 261, in the poor category, on Sunday, up sharply from 117, in the moderate category, on Saturday. On Friday, the AQI had stood at 60, in the satisfactory category, after heavy rain washed pollutants out of the capital's air and gave the city its cleanest October day in four years.
The sudden reversal has caught many residents by surprise, with hazy skies and reduced visibility greeting early morning commuters across the city.
Delhi last recorded very poor air quality on February 11, when the average AQI reached 305. Earlier that month, it had touched 339 on February 4. The Central Pollution Control Board classifies an AQI between 0 and 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. Monday's reading therefore marks the capital's first entry into the very poor band since the winter pollution season began.
The deterioration was widespread. Of the 58 monitoring stations reporting valid readings at 7 am on Monday, 36 recorded very poor air quality, while 53 recorded readings above 200 and 37 registered readings above 300. Jahangirpuri emerged as the worst-affected location, entering the severe category with an AQI of 417.
Punjabi Bagh recorded 398, Rohini 397, Alipur 379, Mundka 376, R.K. Puram 368, Sonia Vihar 367 and Bawana 361. Chandni Chowk recorded 360 and the Jawaharlal Nehru Stadium area 346. Fine particulate matter, or PM2.5, was the dominant pollutant at 51 of the 58 reporting stations, while PM10 was the primary pollutant at the remaining seven.
Sunday had already shown warning signs. Twenty-two of Delhi's 59 monitoring stations recorded very poor air quality on Sunday, while 21 were in the poor category and 14 registered moderate readings. The city's 24-hour average AQI of 261 on Sunday was its highest since April 17, when it stood at 263.
The Air Quality Early Warning System had forecast that Delhi's air quality would remain in the poor category on November 2 and 3 before deteriorating to very poor on November 4. Instead, the capital crossed the 300 mark a day earlier than forecast, and the outlook for the subsequent six days indicates that air quality could remain between the poor and very poor categories.
Two familiar factors are driving the deterioration: stubble burning in neighbouring states and vehicular emissions within the city. According to the Decision Support System for air quality management, stubble burning contributed around 18.57 per cent to Delhi's pollution on Sunday, up sharply from 5.33 per cent a day earlier.
Transport emissions accounted for 16.4 per cent, while industries contributed 3 per cent, residential sources 4 per cent and construction activities 2.2 per cent. Satellite tracking by NASA detected 1,394 farm fires across Punjab and Haryana between October 1 and November 1, a reminder of how quickly crop residue burning can add to the region's pollution burden once the wind turns.
Meteorologists have warned that conditions are unlikely to improve soon. Meteorologist Navdeep Dahiya said no favourable change in weather was expected over the next seven to 10 days, with north-westerly winds and calm conditions allowing emissions to remain suspended in the atmosphere for longer. He noted that most sensors across Delhi-NCR were reporting AQI readings above 300, with many climbing towards the 400 to 500 range.
The combination of falling temperatures, low wind speeds and an approaching festival season is a familiar recipe for worsening smog in the capital.
The worsening air quality coincides with the implementation of additional winter pollution-control measures in Delhi from November 1. Stage I measures under the Graded Response Action Plan came into force on Sunday. Under the new rules, vehicles registered outside Delhi that comply with BS-IV or older emission standards will not be allowed to operate in the city until January 31.
The measures also include curbs on dust-generating construction activities and a 50 per cent cap on physical attendance in government and private offices. Authorities have intensified vehicle checks at the city's entry points, and on the first day of the curbs, 1,500 cars were denied entry and fines of Rs 68 lakh were imposed, according to reports.
Health experts routinely advise residents to limit outdoor exertion when the AQI enters the very poor category, particularly children, the elderly and people with respiratory or heart conditions. Prolonged exposure to PM2.5, the tiny particles that dominate Delhi's pollution at present, can penetrate deep into the lungs and enter the bloodstream.
Doctors advise wearing masks outdoors, keeping windows closed during peak smog hours, and using air purifiers indoors where possible.
For Delhi's residents, the timing is unwelcome. Diwali falls a week away, and firecrackers traditionally push pollution levels sharply higher in the days around the festival, even as enforcement agencies step up checks on their sale and use. With the city's air already in the very poor category before the festival has even begun, officials and experts fear that the coming days could see readings climb further into the severe range if weather conditions remain unfavourable.
The capital has seen this pattern before. Every winter, a mix of local emissions, farm fires, low wind speeds and temperature inversion traps pollutants close to the ground, turning the city's air hazardous for weeks. What makes this year different, so far, is how quickly the situation has changed: from the cleanest October air in years on Friday to very poor air on Monday morning, in the space of a single weekend.
Whether the coming days bring relief or a deeper smog episode will depend largely on the wind, and at present the forecast offers little comfort.
(Reporting based on Outlook India and Hindustan Times.)