What is PM2.5 pollution level in the Air Quality Index?
PM2.5 refers to particulate matter which has a diameter less than 2.5 micrometre. Formed by a mixture of solid pollutants and liquid droplets, the particles can be absorbed into the lungs and bloodstream, and trigger respiratory diseases. Currently, Delhi's PM2.5 level is 20 times higher than WHO standards, according to which it cannot exceed 25 micrograms/cubic metre in 24 hours.