The Environment Pollution (Prevention and Control) Authority has identified air pollution as the fifth biggest killer in India after high blood pressure, indoor air pollution from cooking fuels, tobacco smoking, and poor nutrition. Delhi and Ghaziabad are among the five critically polluted cities that include Gwalior, west Singhbhum, and Raipur. These cities have the highest levels of PM10 or Particulate Matter that refers to harmful suspended particles in the air. Diseases caused by air pollution include strokes, chronic obstructive pulmonary disease, Ischemic heart disease, lower respiratory infections and trachea, bronchus and lung cancer. According to Sunita Narain, the Director General of the Centre For Science and Environment the study shows that half of India's urban population breathes air with particulate levels that exceed permissible limits, while one-third of urban Indians live in critically polluted areas.