An air pollutant generated from the sulfur present in diesel fuel. The concentration of SO2 in the exhaust gas depends on the sulfur content of the fuel. Sulfur dioxide is a colorless toxic gas with a characteristic, irritating odor. Oxidation of sulfur dioxide produces sulfur trioxide which is the precursor of sulfuric acid which, in turn, is responsible for the sulfate particulate matter emissions. Sulfur oxides have a profound impact on environment being the major cause of acid rain. Low sulfur fuels of less than 0.05% sulfur are being introduced for most diesel engine applications throughout the USA and Canada.