Emissions from motor vehicles lead to significant adverse effect on air quality of cities, with many cities reporting ambient air concentration of pollutants well beyond the permissible standards. In this paper, we determine the effect of changing driving patterns during peak and off-peak periods on emissions from diesel passenger cars. Second-by-second emissions of CO, CO2, HC, and NOx were measured during both peak and off-peak periods using portable emission measurement system (PEMS). It is seen that during peak hour, average speed decreases, percentage time spent in acceleration, deceleration, and idling increases, while time spent in cruising mode decreases significantly. Further, EFs are developed for peak and off-peak periods and compared with the Automotive Research Association of India (ARAI) emission standards. The EFs during peak periods are found to be significantly different from off-peak periods. The results of this study would be useful in accurate quantification of emissions. © 2020, Springer Nature Singapore Pte Ltd.