Ž . Sensors and Actuators B 59 1999 195–202 www.elsevier.nlrlocatersensorb Gas detection for automotive pollution control C. Pijolat ) , C. Pupier, M. Sauvan, G. Tournier, R. Lalauze Centre SPIN, ENSMSE, 158 cours Fauriel, Saint-Etienne 42023, France Abstract The detection of the gases produced by the cars becomes an important objective for different applications as urban pollution control or for the development of car exhaust devices. The use of gas sensors can contribute to reach such objectives. At the moment, the performances of the gas sensors available on the market especially SnO sensors are often not sufficient to satisfy these needs. The major 2 limitations are dependent on their poor selectivity and stability. Some examples of such problems are presented through field experiments in both types of applications and some feasible improvements of the sensors are discussed. In urban pollution monitoring, it is necessary to take into account the irreversible action of SO . The dual response to oxidising or reducing gases is a difficult problem to solve, 2 especially for the NO gases. Solutions with metallic filters above the sensing material are currently studied. In order to be able to use x directly the sensors in the car exhausts, new types of sensors are developed mainly on the basis of electrochemical devices. An example of such new sensor is exposed with experimental results obtained on car exhausts. q 1999 Elsevier Science S.A. All rights reserved. Keywords: Gas sensors; Automotive applications; CO and NO pollution x 1. Introduction The detection of gases produced by car pollution be- comes more and more an inescapable need. On one hand, this is necessary for the control of the atmospheric pollu- tion on urban sites which is, for the major part, related directly with car traffic. The different agencies which have the charge to control this pollution have installed in towns some measuring points equipped with analytical apparatus Ž . like infrared IR or UV spectrometers. These methods have a very good accuracy and allow, generally, to deter- mine the exact concentrations of the different gases with- out major problem. Nevertheless, for financial reasons, it is difficult to multiply the number of such pollution control stations. In order to have a better understanding of pollu- tion creation and of the moving of the pollutants, it becomes necessary to study the space distribution of the pollution and consequently to increase the number of measuring points. This can be obtained by the use of gas sensors. In the case of urban pollution, the pollutant gases are especially the gases produced by car, mainly CO, NO x Ž . Ž NO and NO , HC mixtures of burned and unburned 2 . hydrocarbons . ) Corresponding author. Tel.: q33-4-77-42-01-44; fax: q33-4-77-42- 00-00; E-mail: cpijolat@emse.fr The challenge for the development of such gas sensors is moreover important with the requirement of the car manufacturers to use such sensors directly on the cars. Many applications are currently studied. On one hand, some of them concern the air quality in the passenger compartment with a control of the ventilation by filtration w x of the incoming air in case of pollution 1,2 . On the other hand, it is now necessary to measure the concentrations of gases directly in the exhausts. This point becomes more and more strategic for the car manufacturers because the need of gas sensors concerns the control of the motor Ž . optimisation of the combustion rate after motor , the control of the different devices used for post-treatment Ž . three-ways catalysts, DeNO or NO trap devices, etc. x x and also diagnostics of the good efficiency of such cata- Ž . lysts coming rules OBD II, etc. . In both cases, urban pollution or for car control, the major gases to be detected are CO, NO, NO , HC, but also 2 some other gases as SO , CO , O , etc. The required 2 2 3 performances for the sensors, except a low price, are good stability, sensitivity and especially selectivity. This last property is generally difficult to satisfy and at the moment this constitutes the major limitation for the use of gas sensors. The semiconductor sensors are a good illustration of such problem. Actually, the tin oxide sensors are the Ž . only sensors except the oxygen sensors which have been well-developed by various industrial companies and com- 0925-4005r99r$ - see front matter q 1999 Elsevier Science S.A. All rights reserved. Ž . PII: S0925-4005 99 00220-8