Time to breath easy is over, air pollution is reaching critical levels again this winter. Centre for Science and Environment has reviewed the daily air quality data generated by the Central Pollution Control Board as well as the Delhi Pollution Control Committee and the public information system developed by the CPCB and Aria technologies. Officially now air pollution in Delhi is classified into broad bands of healthy, moderate, unhealthy for sensitive groups, unhealthy, harmful, and hazardous. This is based on air quality index.