The objective of this presentation is to evaluate quality of air in terms of emissions of nitrogen oxide released from two stroke and four stroke operating vehicles selected from various industries and to compare the efficiency of engines and fuels (CNG, Petrol and Diesel). It was observed that in 43 samples tested for NOx emissions by - non dispersive infra-red technology (NDIR),  the switching of fuel from gasoline and diesel to compressed natural gas and two strokes to four stroke engines reduce the air emission burden. The concentration of NOx varies in the range from 0.0 to 20.5% for four-stork and 9.4-45.4% in two stroke engines while the reduction in concentration was 0.1 to 0.15 with the use of CNG.