“Delhi has almost twice the concentration of the more lethal pollutant PM1, or particles with diameter less than one micron, as compared to other cities where it is being measured, data from a government agency showed.

According to the data procured by IANS from System of Air Quality and Weather Forecasting And Research (SAFAR), in Delhi 47% of PM2.5 was composed of PM1 during winters, 44% during summers and 61% during monsoon, in 2017.”  Hindustan Times

Read it on Delhiair.org:
Delhi has double concentration of finer, more dangerous pollutant PM1