Air quality monitoring survey conducted by Greenpeace inside five prominent schools in the city also found that the PM2.5 levels were four times more against the prescribed Indian safety limits.
"The real-time monitoring data from all the five schools revealed particulate matter 2.5 to be at very unhealthy levels," a Greenpeace release said.
According to the World Health Organization (WHO), air pollution impacts the most vulnerable sections of the population and children were among the worst hit.
The survey showed that the maximum level of PM2.5 at Greenfield Public School in Vivek Vihar on January 23 was 253.
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It was 209 at the American Embassy School on February 12.
The maximum level of PM2.5 was 243 at Salwan Public School on February 5. At Mirambika School the maximum level of PM2.5 was 251 on January 27. It was 246 at Delhi Public School on February 5.
The International Agency for Research on Cancer classified particulate matter pollution as carcinogenic to humans in 2013, and designated it as a "leading environmental cause of cancer deaths".