HIGHLY SENSITIVE NOX SENSOR FOR ENVIRONMENTAL MONITORING IN TRAFFIC CONTROL SYSTEM

A highly sensitive NOx sensor that can detect NO2 gas in the environmental monitoring level has been developed. The sensor consists of a tetraphenylporphyrin chromium chloride (CrTPP) thin film as a gas-sensitive membrane and a surface acoustic wave (SAW) device as a signal transducer. The change in mass caused by NO2 adsorption on the CrTPP film was measured by a microbalance method using the SAW device. The SAW-type NOx sensor with the CrTPP thin film showed high sensitivity for NO2 and the sensor was found to have no interference for CO, CO2, n-butane, and NO. It is concluded that the sensor is applicable to detect NO2 related to traffic condition in the environmental monitoring level. Correlation analysis between NOx concentrations and traffic volume were carried out near three car exhaust monitoring stations in Tokyo. The traffic volume was found to correlate to the NOx concentrations by taking account of wind speed. A basic concept for traffic control system based on these studies is proposed.