Even the recently-launched smog tower at Connaught Place could not give breathable air to residents nearby on Diwali night as the air quality across Delhi-NCR nosedived to the "severe" zone following rampant cracker bursting, government data showed.
Around 9 pm on Thursday, the 24-metre-high air purifier, considered the first such structure in India, recorded a PM2.5 concentration of 642 micrograms per cubic metre at the inlet and 453 micrograms per cubic metre at the outlet.
The smog tower could only reduce the PM10 level from 649 micrograms per cubic metre to 511 micrograms per cubic metre, as per the readings taken at 9 pm.
The safe limit for the lung-damaging fine particles PM2.5 and PM10 is 60 micrograms per cubic metre and 100 micrograms per cubic metre, respectively.
Earlier, it lowered the PM2.5 concentration from 538 micrograms per cubic metre to 261 micrograms per cubic metre and the PM10 levels from 603 micrograms per cubic metre to 288 micrograms per cubic metre at 9 am.
At 10 am, the PM2.5 concentration was reduced from 481 micrograms per cubic metre to 228 micrograms per cubic metre and the PM10 levels from 544 micrograms per cubic metre to 250 micrograms per cubic metre.
There was no immediate reaction from the office of Delhi Environment Minister Gopal Rai to queries related to the smog tower data.
Official sources, however, said smog towers can "reduce pollution only to a certain extent and one cannot expect the large air purifiers to provide clean air on hazardous air quality days like Friday".
Sunil Dahiya of the Centre for Research on Energy and Clean Air said all environmentalists and scientists have been saying there is no proven record or data globally that establishes that smog towers are effective.
"This experiment at Connaught Place has shown that smog towers can never be a solution to the problem of air pollution. Any further wastage of money on such structures should be stopped immediately. The money should be utilised to reduce pollution at source," he said.
The smog tower, inaugurated by Chief Minister Arvind Kejriwal on August 23, can purify air in a one-km radius around the structure, at a rate of around 1,000 cubic metres per second.
A 16-member team of experts from Delhi Pollution Control Committee, IIT-Bombay, NBCC and Tata Projects has been constituted to study the impact of the air purifier.
The smog tower at Baba Kharak Singh Marg has 5,000 coarse filters and 5,000 fine filters developed by experts at the University of Minnesota which also helped design a 100-metre-high smog tower in Xian, China.
Residents in many parts of Delhi-NCR woke up with an itchy throat and watery eyes as a thick layer of acrid smog engulfed the region on Friday following rampant cracker bursting on Diwali night amid a rapid increase in fumes from stubble burning.
Ahead of the festival season, the Delhi government had announced a complete ban on crackers till January 1, 2022 and ran an aggressive campaign against the sale and use of crackers.
Delhi's air quality index which entered the severe zone last night continued its upward trend and stood at 462 at 12 noon on Friday.
The neighbouring cities of Faridabad (460), Greater Noida (423), Ghaziabad (450), Gurgaon (478) and Noida (466) recorded severe air quality at 12 noon.
An AQI between zero 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.
A likely increase in fumes from farm fires on Friday may worsen the situation, authorities said.
According to the Central Pollution Control Board (CPCB), the 24-hour average concentration of lung-damaging fine particles known as PM2.5 in Delhi-NCR shot up from 243 micrograms per cubic metre at 6 pm on Thursday (Diwali day) to 425 micrograms per cubic metre at 12 noon on Friday, around seven times the safe limit of 60 micrograms per cubic metre.
The PM10 levels crossed the 500 micrograms per cubic metre mark around 5 am on Friday and stood at 554 micrograms per cubic metre at 12 noon.
According to the Graded Response Action Plan (GRAP), the air quality is considered to be in the emergency category if PM2.5 and PM10 levels continue to be above 300 micrograms per cubic metre and 500 micrograms per cubic metre, respectively, for 48 hours or more.