CPCB implements the National Ambient Air Quality Monitoring (NAMP) through a network comprising 523 operating ambient air quality stations covering 215 cities/towns in states and Union territories of the country in compliance with the mandate under the Air (Prevention and Control of Pollution) Act, 1981 to collect compile and disseminate the information on ambient air quality. This report contains ambient air quality data for the year 2011 with ambient air quality analysis of major metropolitan cities of the country. Status of air pollution of various pollutants in the cities has been described in terms of Low, Moderate, High and Critical category vis-à-vis the notified ambient air quality standards. The ambient air quality status is also depicted in the form of trends and percentile figures for ambient air quality locations/cities in the country as well.