United Nations Environment Programme

Print Version

Tool 2: Vehicles and emissions - the influence of technology

Depending on the age and standard of your vehicle, the emissions will differ (See Figure 1).






Figure 1. Effects of vehicle age and use of emission controls and cleaner fuels

Note: Trucks assumed to weight between 6 to 15 tonnes and to be driven in Nairobi. Numbers based on IVE-model developed by J. Lentz.

Age and Technology: The age of vehicles and the use of emission reduction technologies have a great effect on emission levels, i.e. older vehicles emit more than newer ones. This is especially true for older vehicles with mechanical injection systems (typically pre-1990 for passenger vehicles and pre-1994 for trucks). Subsequently, emission standards and regulations mandated the introduction of electronically-controlled fuel and air injections systems that are much more accurate and reliable. Together with the use of unleaded petrol and low sulphur diesel (see Tool 9 and 10and the glossary), these standards have enabled the introduction of emission control technologies (see Tool 11 and 12).

Diesel vehicles (generally comprised of heavy-duty trucks and currently half of all new passenger cars in Europe) are more fuel-efficient compared to petrol vehicles, and thus emit less CO2. However, diesel engines have relatively higher emissions of particulate matter (PM) and nitrogen oxides (NOx).

Petrol-powered vehicles (generally, passenger cars, motorcycles and some light duty trucks) are not as efficient as diesel but emissions of particulate matter and NOx are less. CO emissions are higher for petrol-powered vehicles; however, CO emissions are easily reduced with a catalyst and are not deemed as harmful to human health as particulate matter and NOx emissions.

Motorcycles, 2- stroke or 4- stroke? Many motorcycles, especially in developing countries, today use 2- stroke engines due to their smaller size and lower investment cost. However, 4- stroke engines in motorcycles are available and have several advantages. A 4- stroke engine is much cleaner and emits substantially less volatile organic compounds (VOCs) compared to a 2- stroke engine. A 4- stroke engine will probably cost a little more (10-15%) but uses ~10% less fuel, needs no separate lubricating oil, and requires less maintenance. Modern 2- stroke engines with catalyst and direct injection systems have begun to enter the market. However, so far the endurance of the catalyst is a problem and the cost of a direct injected 2-stroke engine is similar to a 4-stroke engine.

policeThe influence of fuel quality on emissions - lead and sulphur:Lead is/was added to petrol for its anti-knock properties, but is not burnt in the combustion process; instead it is emitted into the atmosphere. Sulphur is naturally found in both diesel and petrol, but is also not burnt in the combustion process and therefore it is emitted as particulate matter and SOx gas.
Lead forms particles that are inhaled and can seriously damage human health. Sulphur is emitted as sulphur dioxide or sulphur trioxide and forms sulphates in the form of fine and ultra-fine particles, which can also seriously affect human health. Both lead and high levels of sulphur inhibit the use of effective emission control technologies.

New technologies: Other currently available vehicle technologies such as natural gas vehicles, biodiesel and ethanol vehicles are described in Tool 13 and 14.

For more info on vehicle emissions >>  www.epa.gov