The main components of vehicle exhaust as carbon monoxide (CO) and nitric oxide (NO) not only pollute the environment, but also do great harm to human body. Since CO and NO have fundamental absorption in mid-infrared wave band, it is suitable to detect them with infrared absorption spectroscopy. A set of apparatus for the measurement of CO and NO with room-temperature pulsed quantum cascade lasers (QCLs) is introduced. This system utilizes long pulsed QCL which produces a complete scan of molecular absorption lines of gases to satisfy the need for sensitivity and rapid response, with a time resolution beyond 1 Hz. It is employed to measure CO and NO from moving vehicles exhausts. The results show its capability of investigating individual plumes. Different characteristics of CO and NO emissions for gasoline and diesel vehicles are also presented. An explanation to the difference is given.