Abstract
Recent research conducted by the Instituut voor Gezondheidstechniek TNO showed that 53% of the air pollutants are produced by traffic. In order to advise repair and service station personnel about simple means of correct adjustment and servicing of engines, the working of four different types of measuring apparatus is described, viz: exhaust fumes testing devices based on heat conducting, exhaust fumes testing devices with after-burning, infrared carbon monoxide meter, and carbon monoxide meter with hydrocarbon indication.