A hazy cocktail of emissions from fireworks, stubble burning and vehicles hung over the national capital a day after Diwali on Monday when the air quality index plummeted to "very poor", the worst-recorded level this season.
The city's air quality index (AQI) stood at 368, a huge improvement over last year when it touched as high as 642, according to data from the Central Pollution Control Board (CPCB) and Delhi Pollution Control Authority (DPCC).
AQI at 4 pm on Sunday was 337.
After last year's Diwali, Delhi's AQI reached as high as 642, which is more than three times the safe limit. The AQI post-Diwali was 367 in 2017 and 425 in 2016.
V K Shukla, in-charge of air quality management at CPCB, said stubble burning, higher vehicular emissions due to the festive season and unfavourable meteorological conditions were the prime reasons for the dip in air quality.
The satellite towns of Ghaziabad (396), Greater Noida (375), Gurgaon (372) and Noida (397) also recorded their AQI in the "very poor" category, according to the CPCB data.
Ambala, Hisar and Kurukshetra in Haryana recorded their AQI at 385, 370, and 392, respectively. In Uttar Pradesh, Muzaffarnagar, Moradbabad and Meerut recorded AQI at 426, 398 and 352.
The AQI in Punjab's Patiala, Ludhiana, Jalandhar and Khanna stood at 349, 353, 377 and 328, respectively.
An AQI between 0-50 is considered "good", 51-100 "satisfactory", 101-200 "moderate", 201-300 "poor", 301-400 "very poor", and 401-500 "severe". Above 500 is "severe-plus emergency" category.
The DPCC said less fireworks, rigorous night patrolling and enforcement measures to curb instigators reduced the PM2.5 and PM10 levels by 30 per cent on Diwali night this year when compared to 2018.
With Delhi's air quality plummeting to dangerous levels around Diwali every year, the Supreme Court had in 2018 banned polluting firecrackers and ordered that only green firecrackers, which is said to cause 30 per cent less pollution, can be manufactured and sold and enforced a two-hour limit for setting them off.
The Arvind Kejriwal government also organised a mega laser show in an effort to dissuade people from bursting crackers.
However, a large number of revellers brazenly flouted the Supreme Court-enforced two-hour limit for bursting crackers this year too.
Green pyrotechnics have also failed to draw good response both from sellers and buyers, primarily due to lack of variety, limited stock and high prices.
Last year also, people continued to buy the conventional firecrackers and use them.
According to the Ministry of Earth Sciences' air quality monitor, SAFAR, levels of PM2.5 tiny particulate matter of diameter 2.5 or less than 2.5 microns that can enter deep into the lungs reached as high as 740 at Delhi University.
Delhi's overall air quality index (AQI) stood at 506 at 6.30 pm, according to the System of Air Quality and Weather Forecasting and Research (SAFAR).
The AQI at Pusa, Lodhi Road, Airport Terminal T3, Noida, Mathura Road, Ayanagar, IIT Delhi, Dhirpur, and Chandni Chowk was 491, 432, 464, 674, 428, 482, 460, 555 and 677, respectively, according to SAFAR data.
SAFAR said an increase in the wind speed will help disperse pollutants and the pollution levels are expected to come down by Tuesday.
It had earlier predicted that Delhi's overall AQI would enter the "severe" category between 1 am and 6 am on Monday, primarily due to firecracker emissions, unfavourable weather and a significant spike in stubble burning.
Kuldeep Srivastava, a senior scientist at India Meteorological Department (IMD), said the spike in pollution levels was a result of unfavourable weather trapping pollutants.
"The wind speed is around 7-8 kilometers per hour and the direction is northwesterly, which is unfavourable. The visibility levels have dropped to around 1,200 metres. Similar weather is likely to prevail over the next two to three days. Only a marginal improvement in air quality is expected," he said.
Last night, people reported violation of the Supreme Court-enforced two-hour window in Malviya Nagar, Lajpat Nagar, Kailash Hills, Burari, Jangpura, Shahdara, Laxmi Nagar, Mayur Vihar, Sarita Vihar, Hari Nagar, New Friends Colony, Hauz Khas, Gautam Nagar, Dwarka among others places.
Residents in Noida, Greater Noida, Gurgaon, Ghaziabad and Faridabad also reported extensive fireworks much beyond the timeframe.
People could also be seen bursting crackers before 8 PM, however, the intensity remained low.