Current Status of Atmospheric Environment and Viewpoints on Motor Vehicle Exhaust Emission Reduction
(1) Current status of the atmospheric environment
Environment standards for air pollution have been prescribed for nitrogen dioxide, suspended particulate matter, photochemical oxidants, carbon monoxide, and sulfur dioxide. In addition, benzene, trichloroethylene, and tetrachloroethylene were included in these environment standards in February 1997. There is concern that exposure to these substances for a prolonged period of time will affect human health, even at very low concentrations. Presently, these substances are monitored continuously.
Measurements from roadside air pollution monitoring stations deployed across Japan have revealed that sulfur dioxide and carbon monoxide concentrations are in good condition but that nitrogen dioxide, suspended particulate matter, and photochemical oxidants are still in a critical state, especially near large cities. In addition, suspended particulate matter and photochemical oxidants are contributing to air pollution over a wider region. Moreover, there are places where the level of hazardous pollutants, such as benzene contained in hydrocarbons, exceeds environmental standards, especially near roadside areas. In recent years, the problem of acid rain has also been spreading over wider areas.
Artificial sources of substances causing such air pollution may be divided into two groups: Mobile generating sources (e.g., motor vehicles) and Stationary generating sources (e.g., factories and business offices).
(2) Formation mechanism of air pollutants and related motor vehicle exhaust emissions
When nitrogen oxides (nitrogen monoxide and nitrogen dioxide) and ozone are exposed to sun light (ultraviolet light) and no hydrocarbons are present in the atmosphere, the concentrations of nitrogen dioxide and ozone in the atmosphere will drop as the concentration of nitrogen oxide dwindles. However, volatile organic compounds, such as hydrocarbons and aldehydes, are present in the actual atmosphere. Consequently, air pollutants (e.g., nitrogen dioxide, ozone, aldehyde, and secondary forming particulate matters) are formed by photochemical reactions, thereby affecting the concentrations of nitrogen dioxide and ozone in the atmosphere. Moreover, some of these substances are involved in the formation of acid rain. Furthermore, air pollution occurs in many places, from local places where air pollution occurs only in vicinity of the generating sources (e.g., air pollution caused by nitrogen dioxide and particles from diesel-powered motor vehicles), to a larger areas where the pollution phenomena is caused by photochemical oxidants, secondary forming particulate matters, and acid rain.
The following explains the mechanism that forms air pollutants. The explanation is based on the knowledge that has become accessible and takes into consideration the kind of motor vehicle exhaust emissions that are related to the reduction of these air pollutants.
- Nitrogen dioxide is emitted directly from exhaust pipes of motor vehicles and other sources. Nitrogen dioxide can also be formed when nitrogen monoxide and ozone react; through the photochemical reaction of nitrogen monoxide and volatile organic compounds, such as hydrocarbons. The rate of nitrogen dioxide formed through photochemical reactions is greatest during the day in winter and spring. Therefore, in order to decrease the concentration of nitrogen dioxide, it is essential to reduce hydrocarbons as well as nitrogen oxides.
- Suspended particulate matters have the following sources: emitted directly through the exhaust pipes of diesel motor vehicles, etc. because of incomplete combustion and secondary formation when a reaction occurs among gases, such as hydrocarbons and nitrogen oxides emitted from exhaust pipes. Therefore, it is imperative to reduce nitrogen oxides and hydrocarbons emitted from gasoline·LPG motor vehicles and diesel motor vehicles in addition to reducing particulate matters discharged directly from diesel motor vehicles.
- Photochemical oxidants are affected by concentrations of nitrogen oxides and hydrocarbons in the atmosphere as well as by meteorological conditions, such as solar radiation rate, ambient temperature, and atmospheric stability. Of these factors, hydrocarbons affect with the formation rate for photochemical oxidants and the formation distribution for high-concentration areas. Therefore, it is mandatory to reduce nitrogen oxides and hydrocarbons to reduce the concentration of photochemical oxidants and to control air pollution over large areas.
- Hazardous air pollutants (e.g., benzene and formaldehydes) are discharged from motor vehicles as a complex substances. Hence, it is imperative to reduce hydrocarbons and particulate matter that constitute the main components of these complex substances.
- Acid rain bears a relationship to nitrogen oxides and ozone, the main components of photochemical oxidants. Therefore, it is imperative to reduce nitrogen oxides and hydrocarbons.
(3) Basic approach to motor vehicle exhaust emission reduction in this Report
In view of the current status of the atmospheric environment described earlier, the formation mechanism of air pollutants, and the possible future growth of the number of motor vehicles in operation, traffic volume, etc., it is necessary to further reduce hydrocarbons, culprits in the formation of many air pollutants, and to reduce nitrogen oxides and particulate matters that are directly related to the concentrations of air pollutants in order to achieve comprehensive improvements in the atmospheric environment. Moreover, with a view to maintaining good quality of the atmospheric environment, it is necessary to further endeavor to decrease carbon monoxide as much as possible along with other substances.
Based on such fundamental concepts, the Experts Committee has closely evaluated the progress of technologies at home and abroad as well as the possibility of technological developments in the future. Furthermore, the Experts Committee has conducted studies on measures for motor vehicle exhaust emission reduction while assessing costs required for these measures.
Furthermore, amid growing concern over a global warming as one of the largest environmental problems faced by humanity today, the Third Conference of Parties to the U.N. Convention on Climate Change (COP3) is scheduled to be held in Kyoto in December of this year. Thus, it has been clearly shown that global warming is a pressing subject to be tackled urgently at home and abroad. Consequently, the Experts Committee has conducted careful studies that will eventually contribute to curbing carbon dioxide emission so that the enforcement of motor vehicle exhaust emission reduction will not hamper the development of fuel economy technologies.
As a result, the Experts Committee has reached the conclusion that it is imperative to carry out the following measures for exhaust emission reduction.
- Considering the recent rapid progress in exhaust emission reduction technology represented by technologies for passenger cars and the increased possibility of future technical development, reduction measures for exhaust emissions from exhaust pipes (exhaust pipe emissions) of gasoline·LPG motor vehicles should be strengthened to emphasize the reduction of emissions of nitrogen oxides and hydrocarbons. In particular, it is necessary to toughen reduction measures for exhaust pipe emissions during cold starts. Moreover, it is indispensable to implement measures that are more effective in maintaining adequate performance of exhaust emission control devices over the entire life of motor vehicles.
- It is necessary to strengthen the measures for fuel evaporative emissions from gasoline motor vehicles to further reduce emissions of hydrocarbons.
- Off-road vehicle emissions contribute about thirty percent of all nitrogen oxides from motor vehicles and about ten percent of all particulate matter. Despite these facts, off-road vehicles are not subject to exhaust emission control regulations. Hence, it is mandatory to implement exhaust emission reduction for these motor vehicles by adding them to the list of motor vehicles subject to exhaust emission control regulations that emphasize the reduction of nitrogen oxides and particulate matter.
Drastic reduction of emissions from diesel motor vehicles has been scheduled to be implemented over a period from 1997 to 1999 in accordance with the 1989 Report. Moreover, a new measure to reduce emissions from two-wheeled motor vehicles has been slated to become effective in 1998 or 1999, according to the 1996 Interim Report. Therefore, the Experts Committee will continue its studies while assessing the effectiveness of these measures.