The W.H.O. report, which examined pollution levels in nearly 1,600 cities in 91 countries for the years 2008 to 2013, found that the annual mean for PM 2.5 concentrations in Delhi was 153 micrograms per cubic meter. Delhi’s reading was almost three times that of Beijing, whose annual mean in the report was 59. Air pollution killed about seven million people globally in 2012, making it the world’s biggest environmental health risk. About 80 percent of those deaths came from heart attacks and strokes, although air pollution also increases lung cancer deaths. Presentation courtesy of Dr. Walter Hays, Global Alliance for Disaster Reduction