VEHICLE MAINTENANCE AND EXHAUST EMISSIONS

In most of the world, light duty vehicles and the engines used in heav y duty vehicles are designed to comply with legal limits for exhaust e missions. The manufacturer must demonstrate that this is the case by s ubmitting vehicles or engines for testing. There is considerable evide nce, though, that many vehicles operating on the roads would not achie ve the appropriate emission standards. Perhaps the main reason for thi s is inadequate maintenance of the vehicles: if engine settings are no t in accordance with manufacturers' specifications, it is not surprisi ng that their performance deteriorates. Methods of addressing this pro blem include requirements on manufacturers to produce durable and stab le components and a compulsory periodic test for vehicles in use. This paper reviews information on emissions from road vehicles in service and how they are related to the vehicle's condition and state of maint enance. The often conflicting criteria for in-service testing are dscu ssed with reference to a number of current and potential test procedur es.