The Delhi government plans to install air purifiers in 38,000 classrooms of government schools, starting with 10,000 in the first phase. Can it help?
Portable HEPA purifiers can substantially lower the level of fine particles inside a closed classroom, so children will inhale less pollution during class time. This reduction matters because it lowers a child’s overall or cumulative exposure to pollution through the day, which is very important for lung health.
(HEPA stands for ‘high-efficiency particulate air [filter]’ that can, in theory, remove 99.9% of dust, pollen, mould, bacteria and airborne particles of 0.3 microns size.)
However, purifiers only clean the air where and when they operate. Students are still exposed while commuting, playing outside, or at home, and these exposures add up. Purifiers, therefore, offer partial protection by reducing indoor exposure during school hours, but they do not replace the need to cut outdoor pollution or protect children before and after school.
Some intervention trials have reported improvements in asthma symptoms, medication use, or short-term respiratory outcomes in children living with high pollution. But evidence on long-term lung growth or permanent protection is limited and mixed.
Recent large classroom trials found lower particles but did not always show clear reductions in viral exposure or illness. Air purifiers do reduce indoor pollution and can help respiratory health in some settings, but they are not a guaranteed long-term fix.
There is evidence that reducing indoor PM2.5 with HEPA filtration can improve symptoms and the quality of life, and reduce medication needs for some children with asthma. Benefits are greater where baseline pollution is high, and when purifiers are used consistently.
Purifiers are not a substitute for medical care, inhalers, or avoiding triggers. But they can be a useful part of a wider plan that includes follow-up with clinicians, trigger control, and inhaler adherence. Results vary by individual and setting.
Effectiveness depends on filter type – it should be true HEPA – and sizing for the room. Units must have proven HEPA filters and a Clean Air Delivery Rate (CADR) or recommended room-coverage that matches the volume of the classroom. Undersized or poorly rated machines move too little air and won’t lower particle levels enough, and can create a false sense of security.
Also, technologies that produce ozone or unproven ionisers should be avoided. Proper selection, placement, and sizing are essential for meaningful protection.
Yes, there is a study. Ventilation air purifiers are considered more helpful as they suck outside air and purify it rather than re-circulate inside air. These air purifiers are especially good for commercial buildings and offices.
Maintenance is critical. Filters clogged with captured particles lose effectiveness and can let polluted air pass through; fans may fail and units can become noisy or energy-inefficient. In poorly maintained settings, a broken or dirty purifier gives little benefit while costing money, and might breed mold if moisture collects.
For government schools, this means budgeting for replacement filters, staff training, simple logs of run hours, and a maintenance plan. Without this, installed machines may not protect children and can create a false sense of safety.
Air purifiers give immediate, local relief indoors but do not address root causes of air pollution. They can protect children during school hours while broader policies are pursued.
Relying on purifiers alone risks diverting attention and funds from long-term actions such as cleaner transport, industrial controls, waste management, and urban planning. The best approach combines short-term indoor protection with sustained public policies to lower outdoor pollution so children are safer everywhere.
(Dr Viny Kantroo is Senior Consultant, Respiratory and Critical Care, Sleep Medicine, Indraprastha Apollo Hospitals)
