Anurag Agrawal of the CSIR Institute of Genomics and Integrative Biology told PTI the cost aspect of installing air purifiers at such a large scale makes it potentially "impractical".
"Air purifiers typically work by trapping the fine particulate matter in HEPA (High efficiency particulate air) filters. These filters need to be replaced frequently otherwise they get blocked," he said.
The Delhi government runs around 1,100 schools.
Anumita Roychowdhury of the Centre for Science and Environment (CSE) said that in a "dynamic environment" like a classroom installing air purifiers does not serve the purpose because even if the room is sealed, its doors will have to be opened and shut frequently.
"That way one will lose what is being purified. It may also lead to a spike in the levels of Carbon dioxide in the room which makes people lethargic. So it is not really the option," she said.
Agrawal said there would not be any increase in the levels of CO2, if purifiers that release strong drafts of air to purify the zone around it are installed. But such purifiers are more expensive.
In its previous circular, dated April 26, the government had not specified on the kind of purifiers it was planning to install.
"The ambient air quality of Delhi needs to be improved. In view of the gravity of harm to human health due to inferior ambient air quality, schools should take action to install air filters as per need," the earlier communication had said.
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