World Health Organization (WHO) has published ‘WHO Air quality guidelines for particulate matter, ozone, nitrogen dioxide and sulphur dioxide’ during the year 2005. The guidelines are intended for reference by countries to provide appropriate targets for a broad range of policy options for air quality management in different parts of the world. The WHO air quality guidelines and interim targets for particulate matter on the basis of 24-hour are enclosed at Annexure-I. The monthly average of PM10 concentration at four locations of Delhi during January 2016 and during September 2016 is enclosed at Annexure-II.
Source: http://www.indiaenvironmentportal.org.in