According to the World Health Organization (WHO), the dubious honour goes to Delhi. It is estimated that air pollution kills 10,500 people in the city every year. The study analyzed the peak levels of fine particulate matter in the ambient (outside) air. It determined that the highest level of airborne particulate matter of PM2.5 (smaller than 2.5 microns) clocked in at 153 micrograms, which is significantly higher than any other city in the world. For example, Beijing, once considered one of the world’s most polluted cities, has a PM2.5 concentration of only 56 micrograms. Delhi’s level is six times the WHO’s recommended maximum and twelve times U.S. standards. High concentrations of pollutants impact lung-health and cause asthma, bronchitis and cancer. Crop burning, coal-fired power plants and heavy vehicular traffic produce most of the particulate matter. Twelve other Indian cities also fell in the top 20 worst offenders on the list. Fuelwood and biomass cake burning for cooking have also left their dirty little mark. A near-permanent brown haze looms over the city and much of the nation. India burns ten times more fuelwood than the U.S. and their stoves are less efficient. Many indoor stoves produce excess smoke that is emitted into the air and inhaled by residents.