With Diwali just a day away, Delhi's air plummeted to "hazardous levels" but bounced back to "very poor" category on Tuesday, leaving people gasping for fresh air.
Meanwhile, air purifiers have been installed at the ITO crossing in Delhi in view of rising pollution levels.
As a thick blanket of haze engulfed the national capital on Monday, experts warned that the air quality is likely to worsen further due to local factors during the festival while doctors said the impact of air pollution on public health can be compared to smoking 15-20 cigarettes a day.
The overall air quality index (AQI) on Monday was registered in the severe category at 397 against 434 a day earlier.
The PM2.5 (particles in the air with a diameter of less than 2.5 micrometres) and PM10 concentrations touched 246 and 372 respectively, both in the very poor category, according to SAFAR data.
on Monday, the PM10 concentration in several parts of Delhi recorded 'severe plus emergency' levels, around 10 times the permissible limit.
The improvement was seen in NCR too as Faridabad, Ghaziabad, Noida and Gurgaon recorded "poor" pollution levels, according to Central Pollution Control Board data.
An AQI between 0 and 50 is considered "good", 51 and 100 "satisfactory", 101 and 200 "moderate", 201 and 300 "poor", 301 and 400 "very poor", and 401 and 500 "severe".
According to a warning issued by the Centre-run System of Air Quality Forecasting and Research (SAFAR), the national capital's air quality is expected to deteriorate to 'severe plus emergency' category after Diwali and it will be "bad" on November 8 even if "partial toxic crackers" are burned compared to last year.
Officials attributed the sudden deterioration in the air quality to a change in wind direction, which is now blowing from the northwestern region towards Delhi and bringing dust and smoke from stubble burning in neighbouring states with it.
Union Environment Minister Harsh Vardhan has warned that strict action will be taken against people violating anti-pollution norms.
Tourists, including foreigners, visiting Delhi ahead of Diwali on Monday complained of having a tough time due to increasing air pollution, with some even cutting short their trips citing health concerns.
Some of them said pollution masks were proving ineffective as the air quality has turned "severe", forcing them to visit hospitals to seek treatment for breathlessness, allergy and irritation.
Meanwhile, a penalty of over Rs 1.2 million was imposed on violators on Monday by the teams deployed to monitor implementation of measures to combat pollution in the Delhi NCR under the Clean Air Campaign, the CPCB said.
The highest number of complaints related to illegal construction and demolition activities stood at 91.
The Delhi Police has seized over 3,500 kg of firecrackers from various parts of the city since October 23 and arrested 26 persons for storing them without the license.
The police have also registered 29 cases following the Supreme Court order on the sale of old firecrackers.