Focusing on vehicles themselves is an effective way to mitigate climate change. By setting strict emission standards for vehicles, improving the quality of fuel processed, and designing cleaner engine technology, the amount of pollutants released would be decreased and the negative effects of climate change can be offset.
Emission standards are standards set by governments which specify limits on the amount of pollutants that can be released into the atmosphere from mobile sources such as vehicles and stationary sources such as industry and power plants. The World Health Organization (WHO) has established air quality guidelines, which can be applied within all regions of the world. They provide uniform standards or targets for ambient air quality. Many countries have set their own national air quality standards that regulate the extent of pollutants in the ambient air. These national standards may be stricter than the WHO guidelines. Typical examples of vehicle emission standards are the European, Japanese and American emission systems. All set emission standards for criteria pollutants such as lead, sulfur dioxide, nitrous oxides, methane, carbon dioxides and particulate matter on the basis of vehicle type. The European emission standards (Euro Standards) are followed by all European Union member countries and many other automobile manufacturing countries in Asia and Africa such as China, India, South Africa and Nigeria. Several non-manufacturing countries have also adopted Euro Standards.
UNECE has released regulations for heavy duty and light vehicles that specify limit values for emissions of particulate matter, carbon monoxide, hydrocarbons and nitrogen oxides. Similar limit values have also been enforced for engines of non-road mobile machinery.
Inspection and maintenance (I/M) measures to control emissions from in-use vehicles are an essential complement to emission standards for new vehicles. I/M programs for gasoline vehicles typically measure hydrocarbon and carbon monoxide concentrations in the exhaust. These have limited effectiveness but can identify gross malfunctions in emissions control systems. iM240 procedure uses dynamometers and constant volume sampling to measure emissions in grams per kilometer over a realistic driving cycle. Inspection and maintenance of high-technology, computer-controlled vehicles can be enhanced substantially with on-board diagnostic systems. For diesel vehicles, smoke opacity measurements in free acceleration are the most common inspection method. However, this approach also has limited effectiveness, but can identify serious emission failures. Opacity measurements can also be used to control white smoke emissions from two-stroke motorcycles. Emissions measured by basic I/M test procedures do not correlate well with emissions measured by more sophisticated tests used to establish vehicle emissions standards, or with actual on-road emissions. These procedures are primarily effective in identifying vehicles with grossly excessive emissions in order to require that those be repaired.
Remote sensing of vehicle emissions is a new technology that could improve the effectiveness of vehicle emissions control programs. The technique works by measuring the absorption of a beam of infrared light by the carbon dioxide, carbon monoxide, and hydrocarbon in a vehicle’s exhaust plume. Based on absorption, a computer is able to calculate the concentration of pollutants in the exhaust as soon as the vehicle passes the device. Although remote sensing offers significant potential for vehicle emissions monitoring and control, the technique has limitations because the measurement is only a snapshot of the emissions and not an average.
On-Board Diagnostic Systems identify and diagnose emission-related malfunctions in vehicles equipped with sophisticated electronic engine control systems, as such malfunctions can greatly increase emissions. The vehicle’s computer system is required to detect failures or loss of efficiency in major emissions-related components and systems, as well as engine misfire, and alerts the user when a malfunction is detected. These systems are able to detect malfunctions that I/M programs miss, such as nitrogen oxide emissions.
Vehicle replacement and retrofit programs are useful in cities in the developing world. Because of the large number of uncontrolled vehicles in operation, new vehicle emissions standards and I/M programs are ineffective at reducing emission levels. Retrofitting existing vehicles with new engines or emission control systems or replacing them with new, low-emitting vehicles can often reduce emissions by 70 percent.
The use of cleaner and lower carbon-density fuels is an important way of improving local air quality and tackling climate change. Major efforts have been made worldwide to gradually remove lead from gasoline. Possible further changes to reduce emissions from gasoline include reduced volatility, increased oxygen content, reduced aromatics, and more widespread use of detergent additives. Conventional diesel fuel can also be improved by reducing the sulfur and aromatic content and by using detergent additives.
Alternative fuels commonly considered for vehicular use are natural gas in compressed or liquefied form, liquefied petroleum gas, methanol made from natural gas, coal or biomass, ethanol made from grain or sugar, vegetable oils, hydrogen, synthetic liquid fuels derived from hydrogenation of coal, and various blends of gasohol. Natural gas and liquefied petroleum gas have significant emission advantages, Hydrogen is a very clean fuel, but is difficult to store and requires a lot of energy to produce. Electricity can reduce pollutant emissions if used for vehicle propulsion, but is costly.
The introduction of ultra-low sulfur diesel (ULSD) can deliver carbon dioxide reductions of 20 to 45%. Local pollutants such as particulate matter and hydrocarbons can also be reduced by up to 97% on the equivalent emissions of standard diesel. However, experts have found levels of NO2 to be in the order of four times higher than for petrol driven equivalent cars. One of the most commonly cited barriers to the introduction of ULSD is its cost due to initial high investment prices for refinery creation.
One fuel-shift taking place is a move towards using biofuels for transport energy, especially in the USA and Brazil. Biofuels have a low carbon footprint, are as energy-efficient as petrol and diesel and have the potential to reduce dependency on imported fuel. Brazil processes bioethanol from sugar cane and soybeans.
Hydrogen fuel is a promising energy source that emits only water at the vehicle tailpipe. It can be derived locally, reducing dependency on imported fossil fuel and can also be heavily compressed, allowing enough of it to be stored on a vehicle for longer-range use between re-fuels.
Environmental assessment of alternative fuels should not be based strictly on vehicle end-use emissions, but should take into account production, storage, and distribution emissions.
Case Study: Iceland is conducting a pilot study, using hydrogen fuel for transport. However, Iceland has comparative advantages in the renewable energy stakes; the country is endowed with large quantities of geothermal energy. More information on future developments can be obtained through the EU's Hydrogen and Fuel Cell Technology Program which is presently structuring socio-economic and technical research into hydrogen fuel.
Vehicle technology improvements can reduce local and global pollutants from individual vehicles. The principal pollutant emissions from vehicles equipped with spark-ignition gasoline engines include unburned hydrocarbons, carbon monoxide and nitrogen oxides. Two-stroke engines, which are generally found in motorcycles, emit high amounts of particulate matter.
Three-way catalysts and electronic engine control systems can reduce hydrocarbons and carbon monoxide emissions by 90-95 percent and nitrogen oxides by 80-90 percent. Lead burn techniques and oxidation catalytic converter can reduce hydrocarbons and carbon monoxide emissions by 90- 95 percent, nitrogen oxides by 60-75 percent and improve fuel economy by 10-15 percent. Catalytic converters process exhaust to remove pollutants. Advanced two-stroke design with fuel infection can reduce fuel consumption by 30-40 percent compared to traditional two-stroke technology in motorcycles. Emissions from diesel engines can be improved by turbo-charging, fuel injection systems, and charge air cooling. Nitrogen oxides and hydrocarbons can be reduced by 50 percent and particulate matter can be reduced by 75 percent. Particulate matter and hydrocarbon emissions can be further reduced through the use of low-sulfur fuel and an oxidation catalytic converter. A trap-oxidizer is a particulate filter in an engine exhaust stream and includes a means of burning collected particulate matter from the filter and can reduce particulate matter by 95 percent.