Air Pollution is typically judged by “PM 10” and “PM 2.5” levels in the atmosphere. PM 10 levels measure pollutants with a diameter of 10 microns or less, while PM 2.5 measure pollutants with a diameter of 2.5 microns or less.
By U.S. standards, for both measurements, a level of more than 201 is classified as “very unhealthy,” and levels higher than 301 are considered “hazardous” to health. Pollution levels above this, “would trigger health warnings of emergency conditions” according to a U.S. government body, which warned that in such a scenario “everyone should avoid any outdoor exertion.”
Over the last few days, the air quality index for PM 10 and PM 2.5 in New Delhi has ranged from 400 to 500, according to data collected by India’s Ministry of Earth Sciences. Early Thursday, the average air quality index for PM 10 was 410 and for PM 2.5 was 417, both levels described by the ministry “very unhealthy.”
In 2010, the capital’s PM 10 averaged 249, according to data from India’s Environment Ministry. That made it India’s most polluted city.