Even the recently installed smog tower at Connaught Place could not give breathable air to residents nearby on Diwali night as the air quality across Delhi-National Capital Region 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 on 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.
Chief Minister Arvind Kejriwal had inaugurated the smog tower on August 23 which, officials say, can purify air in a one-km radius around the structure at a rate of around 1,000 cubic metres per second.
The chief minister had said the construction of more smog towers in the capital would depend on the success of the pilot project.
A 16-member team of experts from Delhi Pollution Control Committee, Indian Institute of Technology-Bombay, National Buildings Construction Corporation Ltd (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.
A thick layer of acrid smog hung over Delhi-NCR on Friday after residents flouted the firecracker ban and emissions from farm fires in the region peaked at 36 per cent, pushing the capital's 24-hour average air quality index for the day after Diwali to 462, the highest in five years.
In neighbouring Noida, the 24-hour AQI was 475, the highest in the country. The neighbouring cities of Faridabad (469), Greater Noida (464), Ghaziabad (470), Gurgaon (472) also recorded 'severe' air pollution levels.
As smog partially blotted out the sun in Delhi and residents complained of itchy throat and watery eyes, the city's environment minister accused the BJP of instigating people to burn crackers by linking it to religion.
Ahead of the festive season, the Delhi government had announced a complete ban on firecrackers till January 1, 2022, and ran a campaign against their sale and use.
