Air pollution has a high risk priority for World and recently some studies have concentrated on its risks for humanity. World Health Organization estimates that 4.6 million people die each year from causes directly attributable to air pollution which damages people, environment, animal and component of natural life. In this paper, a methodology based on Process Capability Indices (PCIs) has been presented for the risk assessment of air pollution. One of the results of PCIs is nonconforming unit which is defined as ratio of items produced out of specification limits. In this paper, main two characteristics of normal distribution, mean, and standard deviation has been taken into account as fuzzy numbers and fuzzy percentage of nonconforming items are calculated for air pollution risk in Istanbul, Turkey.