Of the total 85 cities covered for calculation of AQI during October 2015, 48 cities revealed good air quality, 62 cities revealed satisfactory air quality, 33 cities revealed moderate air quality, 8 cities indicate poor air quality, 3 cities (Delhi, Devangere, Karnataka and Lucknow, Uttar Pradesh) cities showed very poor air quality and 2 city (Delhi, Lucknow-Uttar Pradesh) showed severe air quality. Air Quality Index is a tool for effective communication of air quality status to people in terms, which are easy to understand. It transforms complex air quality data of various pollutants into a single number (index value), nomenclature and colour. There are six AQI categories, namely Good, Satisfactory, Moderately polluted, Poor, Very Poor, and Severe. Each of these categories is decided based on ambient concentration values of air pollutants and their likely health impacts (known as health breakpoints). AQ sub-index and health breakpoints are evolved for eight pollutants (PM10, PM2.5, NO2, SO2, CO, O3, NH3, and Pb) for which short-term (upto 24-hours) National Ambient Air Quality Standards are prescribed. Based on the measured ambient concentrations of a pollutant, sub-index is calculated, which is a linear function of concentration (e.g. the sub-index for PM2.5 will be 51 at concentration 31 μg/m3, 100 at concentration 60 μg/m3 and 75 at concentration of 45 μg/m3). The worst sub-index determines the overall AQI.