National mean Concentration with 90th percentile and 10th percentile for Sulfur dioxide , Nitrogen dioxide and Particulate matters 10 is depicted in Figure 9.2 National mean of Sulfur dioxide concentration has decreased over the years indicating that there has been a decline in Sulfur dioxide levels (Figure 9.2a). Decreasing trend may be due to various interventions that have taken place in recent years such as reduction in sulphur in diesel , use of cleaner fuel such as CNG in metro cities, change in domestic fuel from coal to LPG etc.