For years, Delhi has been living with the idea that closing doors and stepping indoors provides protection from toxic air. A week-long HT field experiment challenges that belief. By tracking particulate matter inside a school, AIIMS, a special pollution clinic and a house, the journalists found that the city’s most vulnerable people – children, patients, pregnant women – were breathing polluted air as often indoors as outside. Only in a tightly controlled indoor environment, with the air purifier running continuously, could pollution be reduced to safe levels.
In classrooms, the air is barely better than in a parking lot
While most parents may see schools as sanctuaries from the smoke outside, the air inside a private school in Rohini’s Sector 5 tells a sobering story. As HT tracked the air quality inside and outside the campus – in several schools across the city, where there are no air purifiers in classrooms, it found figures that left little room for reassurance.
Outside the school gate and bus parking area, PM2.5 levels ranged from 246μg/m³ to 502μg/m³. Indoors, in places where children spend most of their day – closed classrooms, computer labs and even the principal’s office – readings ranged from 188μg/m³ to 404μg/m³. The readings showed that in corridors and semi-sheltered areas, pollution levels were almost indistinguishable from outside areas. These readings were between three to seven times the safe level of 60μg/m³ as per Indian standards.
Since this exercise took place during regular school hours, curious students came to observe the findings. Most of them were shocked to know the level of pollution they were exposed to despite being inside the school.
A Class 5 student said, “I take off my mask only when I am inside the school and carry hot drinking water with me to ensure that I am drinking dust-free water. But, with this level of pollution around me, I feel my efforts will do little to make things better.”
On the first day of monitoring, January 14, PM2.5 levels at the parking lot and playground were 308 µg/m³ and 297 µg/m³. Indoors, the readings dropped marginally – 236μg/m³ in the principal’s office, 231μg/m³ inside a classroom and 248μg/m³ in the computer lab. Pollution remained in the same range over the next two days, before increasing rapidly after January 16.
January 17 was the worst day of practice. In the parking bay, PM2.5 reached 502μg/m³ – the highest single reading recorded at the school during the week. Indoors, the air offered little respite: 432µg/m³ in the principal’s office, 421µg/m³ in the computer lab, 399µg/m³ in the counselor’s room and 435µg/m³ in the corridors. This coincides with Delhi’s widespread pollution spike, when the city’s 24-hour average AQI reached 400.
The school remained closed on Sunday, but when monitoring resumed, the pattern remained intact. On the sixth day, PM2.5 outside the main building was 451μg/m³. Inside, readings in offices, laboratories and corridors ranged from 404μg/m³ to 444μg/m³. Even on the final day, when outdoor pollution came down slightly to 364μg/m³, indoor levels remained between 301μg/m³ and 339μg/m³.
Throughout the week, not a single reading was in line with India’s safety standard of 60μg/m³. The highest daily average of 434.8μg/m³ was recorded on day 4. Even the “best” day average was 206.2μg/m³ – still more than three times the national safe limit.
Principal Jyoti Arora said the findings raise difficult questions. “We have a green campus, cleanliness is our top priority, and during high pollution months we limit outdoor activities,” he said. “But with pollution at these levels, I am not sure what else can be done at the school level. Amidst all this, meeting the norm of 220 academic days becomes a challenge.”
For some teachers, the data has become a lesson in itself. A senior coordinator said the crisis provides a big teaching moment. “It’s an eye-opener for students. It shows why respecting the environment is no longer optional – it’s essential.”
Even wards treating the most vulnerable have polluted air
At Delhi’s premier public hospital, the All India Institute of Medical Sciences (AIIMS), the hope is that the sick will find safety within its walls. Yet a week-long monitoring exercise inside two of its most sensitive locations – Dr BR Ambedkar Institute Rotary Cancer Hospital and Mother and Child Block – revealed that PM2.5 levels continued to be well above what is considered safe.
Inside the cancer ward, where immunocompromised patients spend hours every day, the lowest PM2.5 reading recorded was 201µg/m³ on January 15 – more than three times India’s 24-hour safety limit. The worst reading logged on January 17 reached 431µg/m³.
Fine particles at these levels are known to penetrate deep into the lungs and bloodstream, increasing the risk of respiratory illness, inflammation, and weakened immunity – these dangers are especially serious for cancer patients undergoing chemotherapy or radiation. The peak rush of patients is also in the early morning, when readings are taken, further increasing exposure.
On January 17, the day when the average pollution level at AIIMS was highest, PM2.5 outside the cancer ward was 412μg/m³. Inside the waiting room, it measured 328μg/m³, which dropped slightly to 249μg/m³ in the corridor.
Among those who came forward was 17 year old Anmol, who was undergoing treatment for brain cancer. “On OPD days, we stay here for four to five hours. On radiation days, we spend the whole day here,” he said. “Doctors warn us about infection, but most patients don’t even know how bad the air is. It feels like we’re coming to a more infection-prone place to get treatment.”
The situation was hardly better in the maternal and child block, which houses gynecology and pediatric OPDs, surgery wards and neonatal units. PM2.5 levels there ranged from around 120μg/m³ on the best day to over 400μg/m³ on the worst day in some parts of the ward. On 14 January, 123μg/m³ was recorded in the main waiting area. Five days later, the same location recorded 431μg/m³ – seven times more than the national limit.
On most days, readings remained between 180μg/m³ and 270μg/m³, indicating sustained exposure rather than short-term spikes.
Kamla, who had traveled from Gwalior with her two-year-old child for liver treatment, said the findings were disturbing. “We take precautions – masks, cabs, avoiding going out. But if the air inside the hospital is also this bad, what can we do?”
Public health experts have warned that such conditions pose serious risks. A pulmonologist said patients with weakened immune systems, pregnant women and children are particularly vulnerable, as prolonged exposure can increase inflammation, lead to infection and weaken recovery.
A special ‘pollution clinic’ battling poisonous air
A special air pollution clinic was set up at Delhi’s Ram Manohar Lohia (RML) Hospital to treat diseases caused by toxic air. Yet even here, clean air remains elusive. During a separate monitoring exercise on Monday – the only day the clinic operated – PM2.5 levels inside the facility were recorded at 216µg/m³ around 2pm. This is 3.5 times India’s national safety limit and is strongly in the “harmful” category, especially for patients who already suffer from pollution-related diseases.
Located on the ground floor, the clinic provides integrated care across pulmonology, cardiology, ENT, ophthalmology, dermatology and psychiatry, acknowledging the multi-systemic impact of air pollution. Every Monday, 60 to 80 patients walk through its doors, with the number of patients increasing rapidly during the winter.
Health experts say that in such situations, polluted indoor air can weaken the treatment. “Most patients coming to air pollution clinics already have compromised respiratory health,” said Dr Arun Kumar Giri, director of surgical oncology, Aakash Healthcare. “Exposure to polluted air inside hospital premises can aggravate symptoms and delay recovery. Clean air here is essential, not optional.”
Clean indoor air is possible – but only with purification and constant vigilance
HT’s surveillance inside a house in Vikaspuri, west Delhi, shows that the refuge offered by a house from pollution is conditional at best. Doors closed, windows sealed and purifiers on full blast – it’s the only way to breathe clean air at home.
By running the air purifier in the bedroom, PM2.5 levels dropped to 18µg/m³ – an ideal scenario and a glimpse of what safe air could look like. On most days, the purifier’s readings range between 20μg/m³ and 50μg/m³. Turn the machine off, however, and pollution increased rapidly, often to four or five times the national limit.
The exercise began on 14 January with the purifiers being shut down. At 10 am, PM2.5 was 338μg/m³. Within minutes of turning on the purifier, the levels started falling – 129μg/m³ by 10.11am, 74μg/m³ by 10.15am and below 60μg/m³ by 10.20am. For the next hour, the readings remained roughly between 20μg/m³ and 40μg/m³.
On January 20, exactly the opposite happened. With the purifier running, PM2.5 remained below 30μg/m³. Ten minutes after it was switched off, levels rose to 238μg/m³ – this despite the doors and windows being closed.
Experts say this reflects how most homes are built. “We assume homes are airtight, but they rarely are,” said Arun Sharma, professor of community medicine at UCMS. “When pollution is high outside, it leaks indoors almost immediately. Indoor sources like cooking, incense and room fresheners can make it worse.”
Unless Delhi’s outdoor air improves, clean indoor air will remain a privilege – relying entirely on machines, vigilance and constant purifying power, Sharma said.
