In recent years the concern about the behaviour of oxides of nitrogen (NOx: NO, NO2) in atmosphere has increased considerably. NOx undergoes various complex atmospheric reactions to generate secondary pollutants which are known to cause severe adverse effects on human health. This work focuses on the study of physical and chemical fate of NOx released in the atmosphere from vehicles, which are the main sources of atmospheric NOx. Keeping the objective and standard guidelines for monitoring in view, two typical sites near the road with high vehicular density were chosen for the study. One site was a relatively cleaner area with only vehicles as major source of pollution, and the second site was a traffic junction in an industrial region, where pollution levels are amongst the highest in Mumbai. Ambient monitoring of NOx was done for 24 hr continuously using chemiluminescent NOx analyser. The data was used to analyse temporal and spatial variation of NO, NO2 and NOx and their atmospheric chemical reactions. The monitoring results show that at larger distance from the road the level of NO decreases but the concentration of NO2 which is very harmful remains the same. Statistical analysis is conducted to establish the relationship between likely change in NO2 concentration as a result of NOx emission changes.