Platinum Metals Rev., 1989, 33, (4), 194
Controlling Motor Vehicle Emissions
An Assessment of the Implications for Climate Modification
For some twenty years this Journal has reported advances in the application of platinum metals catalyst technology for the control of automobile exhaust gases. The first work was directed at reducing atmospheric pollution in Los Angeles, where climatic and topographic conditions, together with a high concentration of automobiles combined to create a clearly perceived problem. Since that time the use of pollution control catalysts for vehicle emission abatement has grown substantially. In Europe, popular concern about the effects of pollution is now being translated into legislation to protect the environment, so it is timely to re-examine the existing evidence of the atmospheric changes caused by motor vehicles, and from that to predict what may happen on a global scale in the future. It is suggested by the author, who was formerly Deputy Assistant Administrator for Mobile Source Air Pollution Control at the U.S. Environmental Protection Agency, that the latest catalyst technology must be applied worldwide, without delay, to prevent further major damage to the environment.
Motor vehicles using petrochemical fuels emit significant quantities of carbon monoxide, unburnt hydrocarbons, nitrogen oxides, fine particles of solids, and lead, each of which in sufficient quantities can cause adverse effects on health and on the environment. Because of the growing number of vehicles in use, and the high levels of emissions from them, serious air pollution problems have become an increasingly common phenomena in modern life. Initially these problems were most apparent in city centres, but recently rivers, lakes and even forests, have also experienced significant degradation. As more and more evidence accumulates of the impact that some of man’s activities are having on the upper atmosphere, so concern is increasing that motor vehicles are contributing not just to local or regional pollution but also to global changes which could modify the climate of the entire planet.
In an effort to minimise the problem of motor vehicle pollution, emission rates from cars have been limited since the 1960s. Starting in 1975, the pace of control was accelerated with the introduction of oxidation catalytic converters on cars in the United States of America. Now these have been replaced by three-way converters which can lower carbon monoxide, hydrocarbons and nitrogen oxides emissions simultaneously, and increasingly this technology is being applied to vehicles all across the world. Catalytic technology using platinum group metals is now routinely applied to vehicles in Austria, Australia, Canada, the Federal Republic of Germany, Japan, the Netherlands, South Korea, Sweden, Switzerland and the United States. Within the next few years Brazil, Mexico, Taiwan, and most European countries are scheduled to join their ranks.
To date, the primary impetus for these controls has been concern about pollution of the troposphere, which is the lower part of the atmosphere that extends from the surface of the earth to an altitude of between 9 and 17 kilometres. Now, however, evidence shows that the control of carbon monoxide, hydrocarbons and nitrogen oxides is also necessary to reduce the risk of global warming that could result from changes in the upper atmosphere.
Human activity can increase global warming by changing the chemistry of the atmosphere in two ways: by allowing more rays from the sun to reach the surface of the planet, and by reducing the opportunity for rays to escape from the earth. In the face of “irrefutable evidence” that the chemistry of the upper atmosphere is changing, physical evidence linking these changes to global warming, and “observational evidence” that the earth is in fact warming, political and policy oriented institutions and individuals have increasingly focused their attention on the problem of global warming (1).
The two major human activities that are considered to cause these changes are the combustion of fossil fuels and the release of chlorofluorocarbons. The former leads to the emission of carbon dioxide and other so called “greenhouse gases” which have been shown to be accumulating in the atmosphere in recent years, while the latter can destroy the protective ozone layer which shields the earth from harmful ultraviolet radiation from the sun. Perversely, while the depletion of ozone in the upper atmosphere is the cause of great concern, its formation and accumulation at ground level by the reaction in sunlight of volatile organic compounds, including hydrocarbons, with nitrogen oxides can also be damaging to health, and to plant life.
Several factors have increased the fear regarding global warming and influenced the perception of its severity. First has been the rapid development of a hole in the ozone layer over the Antarctic, which shows that human activity is actually causing modifications to the upper atmosphere, and that once such modifications begin they can proceed at a rapid and not fully understood rate. Indeed, new evidence suggests the presence of a similar but smaller hole over the Arctic. Second there is clear evidence that global atmospheric concentrations of carbon dioxide, methane, nitrous oxide, carbon monoxide and other gases are increasing, and either directly or indirectly, each of these has the potential to exacerbate the greenhouse effect (2). Finally, the average global temperature already appears to be increasing, as shown by the fact that four of the warmest years in this century have occurred this decade; worldwide, 1988 appears to have been the hottest year in the last one hundred and thirty, during which detailed records have been kept (3). In the north-eastern U.S.A., at one point, there were over 40 consecutive days with temperatures in excess of 32°C, a factor which contributed to the highest tropospheric ozone levels in a decade (4).
While the global temperature cycle is not fully understood and can be influenced by many factors, the combination of factors noted above has led highly reputable scientists to conclude that global warming is already occurring as a result of the greenhouse effect (5, 6). For example, Dr. James Hansen, the head of the National Aeronautics and Space Administration’s Goddard Institute for Space Studies, told a Senate subcommittee that it is “time to stop waffling so much and say that the evidence is pretty strong that the greenhouse effect is here” (7). Others who feel that the linkage between the greenhouse gases and global warming is still tenuous, none the less seem to be leaning toward some precautionary controls at this time because the potential adverse impact could be so severe. This latter view is reinforced by the lessons of the ozone hole. Clearly we do not understand fully the phenomena but once it starts, if it starts, it may proceed much more quickly than we currently anticipate and lead to results we cannot predict. As recently noted in Science :
“the possibility that a considerably larger, though less likely, temperature rise presents the greater risk remains ignored. The latter eventuality is more to be feared, principally because of the high cost of its effects, the draconian and expensive steps needed to avert it, and the time required, first, to obtain global agreement on the need to act, and then to transmute world energy production into a non fossil-fuel-using system.” (8)
Many observers now agree that motor vehicles already play a significant role in the climate modification problem, and have the potential to play an even greater role in the future. The purpose of this analysis is to examine that role and its likely future direction. First, an assessment will be made of the important greenhouse gases and the current significance of vehicle emissions. Then, historical and likely future trends in vehicles and their use will be summarised. Finally, the overall effect of vehicles and emission control technologies on future climate modification will be assessed.
|Pollutant||Total amount||Vehicle emissions|
The Role of the Motor Vehicle in Climate Modification
Important Greenhouse Gases
Important greenhouse gases include carbon dioxide, some of the chlorofluorocarbons (CFC-11, CFC-12), methane, nitrous oxide, ozone and the compounds which cause ground level ozone to form, hydrocarbons, and the other oxides of nitrogen. On a global scale, each of these gases has been increasing in recent years. As noted in a recent report:
“The concentrations of halocarbons, methane, nitrous oxide (N2O), odd nitrogen and carbon monoxide appear to be increasing at present on a global basis, by 5% per year for CFC-11 and CFC-12, 7% per year for CH3CCl3, 1 percent a year for CH4, 0.2% per year for N2O and 1 to 2% per year for CO”. (9)
Concentrations of ground level ozone are increasing, and stratospheric ozone is being destroyed globally. During the Antarctic spring a “hole” the size of North America is depleted of ozone and, at certain altitudes, is destroyed almost completely because of man-made chemicals (10). Researchers who recently re-analysed a set of European data on tropospheric ozone concentrations from the turn of the century concluded that ozone concentrations had doubled over the last 100 years (11). One commentator described the finding “as remarkable as the observation of a hole in the stratospheric ozone layer over Antarctica and potentially is just as consequential” (12). An analysis of several sites indicates that tropospheric ozone background levels are increasing at a rate of 1 to 3 per cent per year, with overall nitrogen oxides increases being the controlling factor (13).
Likely Effects of Climate Modification
Over the next fifty years, increasing concentrations of tropospheric ozone and other greenhouse gases are projected to result in an increase in the global average temperature of between 1.5 and 4.5°C. Changes likely to accompany this temperature increase include stratospheric cooling, an increase in global mean precipitation, reduction of sea ice, polar winter surface warming, summer continental dryness, precipitation increase in high latitudes, and a rise in global mean sea level. Most of these changes should occur gradually. The U.S. Environmental Protection Agency (E.P.A.) has recently estimated that average sea levels will rise 5 to 15 inches above current levels by the year 2025, if events develop as anticipated (14); however, the Antarctic ozone hole experience reinforces the anxiety that is associated with any such significant and poorly understood phenomena, because of the risk that chemical modifications once initiated may proceed at a faster rate than is generally anticipated at present.
Complex Inter-Relationships between Gases
Some of the previously mentioned compounds react with each other in ways which have been understood only recently. For example, hydroxyl radicals (OH), which scavenge many anthropogenic and natural trace gases from the atmosphere, are themselves removed by carbon monoxide (15, 16). This was summarised by Ramanathan in a recent Science article:
“The highly reactive OH is the primary sink for many tropospheric gases and pollutants including O3, CH4, CO, and NO. Hence, increases in CH4, such as those during the last century [135% increase] could have caused a substantial (20 to 40%) reduction in OH, which in turn, could cause an increase in tropospheric O3 by as much as 20%. Since CH4 oxidation leads to the formation of H2O, an increase in CH4, an important greenhouse gas, can lead to an increase in H2O in the stratosphere. Likewise, an increase in the CO concentration can tie up more OH in the oxidation of CO. Thus, through chemical reactions, an increase in either a radiatively active gas such as CH4 or even a radiatively inactive gas such as CO can increase the concentration of several important greenhouse gases.” (2)
Thus carbon monoxide emissions are very important for climate modification. This point was reinforced by Dr. Gordon MacDonald at a recent World Resources Institute Symposium:
“Carbon monoxide could thus be indirectly responsible for increasing greenhouse warming by 20 to 40% through raising the levels of methane and ozone. … Carbon monoxide participates in the formation of ozone, and also in the destruction of hydroxyl radicals, which are principal sinks for ozone and methane greenhouse gases. Because carbon monoxide reacts rapidly with hydroxyl, increased levels of carbon monoxide will lead to higher regional concentrations of ozone and methane. Measures to reduce carbon monoxide emissions will assist in controlling greenhouse warming.” (17)
This is especially significant in view of the evidence that global carbon monoxide levels are now also increasing. As recently noted by Khalil and Rasmussen:
“the average tropospheric concentration of CO is increasing at between 0.8% and 1.4% per year, depending on the method used to estimate the trend, and the 90% confidence limits of the various estimates range between 0.5% and 2.0% per year.” (18)
Motor Vehicles Emit Many of These Gases
Motor vehicles generate more air pollution than any other single human activity. Greenhouse gases emitted by, or attributable to, motor vehicles include chlorofluorocarbons, carbon dioxide, nitrous oxide, methane, and the precursors to ground level ozone, namely, hydrocarbons and the other nitrogen oxides (19). Chlorofluorocarbons. These are the most potent greenhouse gases and are now responsible for about 15 to 20 per cent of the total global warming effect (2). About 40 per cent of the United States production of chlorofluorocarbons and 30 per cent of European production is devoted to air conditioning and refrigeration. Mobile air conditioning accounted for 56,500 metric tons of chlorofluorocarbons—28 per cent of the chlorofluorocarbons used for refrigeration in the United States, or about 13 per cent of total production. In contrast, home refrigerators accounted for only 3,800 metric tons (20). Thus, approximately one of every eight pounds of chlorofluorocarbons manufactured in the U.S.A. is used, and emitted, by motor vehicles. Chlorofluorocarbons are also used as a blowing agent in the production of seating and other foamed products but this is a considerably smaller vehicular use.
Carbon dioxide is the other major greenhouse gas. A single tank of gasoline produces between 300 and 400 pounds of carbon dioxide when burned. Motor vehicles emit almost 15 per cent of the world’s output; in the U.S.A. motor vehicles are responsible for about 25 per cent of the total carbon dioxide emissions (19).
Carbon monoxide, hydrocarbons and nitrogen oxides. In 1985, in the U.S.A., transportation sources were responsible for 70 per cent of the carbon monoxide, 45 per cent of the nitrogen oxides, and 34 per cent of the hydrocarbons. For transportation sources other than highway vehicles, that is air, rail and marine transport, the U.S. Congressional Office of Technology Assessment (O.T.A.) recently concluded that mobile sources were actually responsible for almost 40 per cent of total nationwide volatile organic compounds (V.O.C.). As illustrated in Figure 1, the only other major source category which this Office found to be responsible for amounts approximating to those from mobile sources in 1985 was organic solvent evaporation (21). Based on recent preliminary data regarding evaporative “running losses”, the hydrocarbon contribution from vehicles may actually be substantially higher; running losses could exceed 1.5 grams per mile (22).
Motor vehicles also dominate the emissions inventories of most European countries. The Organisation for Economic Co-operation and Development (O.E.C.D.) recently noted that:
“The primary source category responsible for most NOx emissions is road transportation roughly between 50 and 70 per cent. … Mobile sources, mainly road traffic, produce around 50 per cent of anthropogenic VOC emissions, therefore constituting the largest man-made VOC source category in all European OECD countries.” (23)
Beyond the U.S.A. and Europe, the Table shows that, for countries belonging to the O.E.C.D. as a whole, motor vehicles are the dominant source of carbon monoxide, oxides of nitrogen, and hydrocarbons (24).
These Pollutants Cause Other Adverse Effects
While climate modification is the primary focus of this study, it is important to note that many of the same pollutants which cause or contribute to that problem, also contribute substantially to adverse health effects in many individuals, in addition to harming terrestrial and aquatic ecosystems, causing crop damage, and impairing visibility. Some of these other effects will be described below.
Tropospheric Ozone. Photochemical smog results from chemical reactions involving both hydrocarbons and nitrogen oxides in the presence of sunlight. While historically the major strategy for reducing smog has focused on tight restrictions on hydrocarbon emissions, nitrogen oxide control is also necessary. A prominent researcher in this field has noted that:
“Recent research results from our research group indicate there is a critical need to consider controls on both nitrogen oxides and reactive hydrocarbons if overall oxidant levels are to be lowered. … A critical implication of these findings is that without controls on nitrogen oxides the current control policies will simply change the urban ozone problem into a regional scale one.” (25)
The ozone problem is a special concern. First, the problem is widespread and pervasive, and appears likely to be a long term problem in many areas of the world unless further significant controls are implemented. For example, almost 80 million Americans currently reside in areas where the amount of ozone exceeds the current air quality standard (26, 27); many of these individuals suffer eye irritation, cough and chest discomfort, headaches, upper respiratory illness, increased asthma attacks, and reduced pulmonary function as a result of the ozone levels.
In addition, the current air quality standard tends to understate the health effects. For example, as noted by E.P.A. Administrator Lee Thomas, new studies indicate:
“that elevated ozone concentrations occurring on some days during the hot summers in many of our urban areas may reduce lung function, not only for people with pre-existing respiratory problems, but even for people in good health. This reduction in lung function may be accompanied by symptomatic effects such as chest pain and shortness of breath. Observed effects from exposures of 1 to 2 hours with heavy exercise include measurable reductions in normal lung function in a portion (15–30 per cent) of the healthy population that is particularly sensitive to ozone.” (26)
Other studies presented at the recent U.S.-Dutch Symposium on ozone indicate that healthy young children can suffer adverse effects from exposure to ozone at levels below the current air quality standard (28). Numerous studies have also demonstrated that photochemical pollutants inflict damage on forest ecosystems and seriously affect the growth of certain crops. (29)
It is important to note that global warming may have a significant impact on local ozone air pollution episodes. As recently pointed out by the American Lung Association:
“the increase in ultraviolet B radiation resulting from even a moderate loss in the total ozone column can be expected to result in a significant increase in peak ground based ozone levels.”
… “these high peaks will occur earlier in the day and closer to the populous urban areas in comparison to current experience, resulting in a significant, though quantitatively unspecified, increase in the number of people exposed to these high peaks.” (30)
Furthermore, tropospheric ozone is a greenhouse gas. Ozone absorbs infrared radiation and increased ozone concentrations in the troposphere will then contribute to climate modification.
Carbon Monoxide. Exposure to carbon monoxide results almost entirely from motor vehicle emissions, although in some localised areas, wood burning stoves also significantly affect carbon monoxide levels. While there has been progress in reducing ambient carbon monoxide levels across Europe, Japan and the United States, the problem is far from solved. For example, approximately 85 major metropolitan areas in the U.S.A., with a total population approaching 30 million, currently exceed the carbon monoxide air quality standard. In fact, E.P.A. Administrator Lee Thomas indicated in Congressional testimony that as many as 15 areas in the United States may have intermittent carbon monoxide problems that could prevent attainment of this standard for many years (26).
This problem is important because of the clear evidence relating carbon monoxide exposure to adverse health effects. For example, in a recent assessment conducted under the auspices of the Health Effects Institute, it was concluded that:
“These findings demonstrate that low levels of COHb produce significant effects on cardiac function during exercise in subjects with coronary artery disease.” (31)
Further, in another recent study of tunnel workers in New York City, the authors noted:
“Given the magnitude of the effect that we have observed for a very prevalent cause of death, exposure to vehicular exhaust, more specifically to CO, in combination with underlying heart disease or other cardiovascular risk factors could be responsible for a very large number of preventable deaths.” (32)
In addition, as noted earlier, recent evidence indicates that carbon monoxide may contribute to elevated levels of tropospheric ozone (17).
Oxides of Nitrogen. A variety of adverse health and environmental effects are produced by nitrogen oxides emissions from vehicles and other sources. These emissions also react chemically with other pollutants to form ozone and other highly toxic pollutants. Next to sulphur dioxide, nitrogen oxides emissions are the most prominent pollutants contributing to acidic deposition.
Exposure to nitrogen dioxide emissions is linked with increased susceptibility to respiratory infection, increased airway resistance in asthmatics, and decreased pulmonary function (33). While the annual average national air quality standard is currently attained in most areas of the U.S.A., short term exposures to nitrogen dioxide have resulted in a wide range of respiratory problems in school children, the most common being coughs, runny noses and sore throats, as well as increased sensitivity to bronchoconstrictors by asthmatics (34, 35).
The World Health Organisation concluded that a maximum 1 hour exposure of 190 to 320 micrograms per cubic metre (0.10–0.17 ppm) should be consistent with the protection of public health, and that this exposure should not be exceeded more than once per month. The State of California has also adopted a short term nitrogen dioxide standard, 0.25 ppm averaged over one hour, to protect public health.
Oxides of nitrogen have also been shown to affect vegetation adversely. Some scientists believe that these oxides are significant contributors to the dying forests that are seen throughout central Europe (36). This adverse effect is even more pronounced when nitrogen dioxide and sulphur dioxide occur simultaneously. Furthermore, nitrogen dioxide has been found to cause deleterious effects on a wide variety of materials, including textile dyes and fabrics, plastics and rubber, and is responsible for a portion of the brownish colorations in polluted air or smog.
Acid deposition results from the chemical transformation and transport of sulphur dioxide and nitrogen oxides. The latter emissions are responsible for approximately one-third of the acidity of rainfall. Recent evidence indicates that the role of nitrogen oxides may be of increasing significance with regard to this problem:
“Measurements of the nitrate to sulphate ratio in the atmospheric aerosol in southern England have shown a steady increase since 1954. The nitrate content of precipitation averaged over the entire European Air Chemistry Network has steadily increased over the period 1955 to 1979. The nitrate levels in ice cores from South Greenland have continued to increase steeply from 1975 to 1984, whilst sulphate has remained relatively constant since 1968. The ‘Thousand Lake Survey’ in Norway has recently revealed a doubling in the nitrate concentration of 305 lakes over the period 1974–1975 to 1986, despite little change in pH and sulphate.” (37)
Several plans to control acid deposition have targeted on reductions in nitrogen oxides emissions, in addition to substantial reductions in sulphur dioxide. The participating countries at the 1985 International Conference of Ministers on Acid Rain undertook to “take measures to decrease effectively the total annual emissions of nitrogen oxides from stationary and mobile sources as soon as possible.” (38)
Conclusions: Vehicle Emissions and Climatic Modifications
Emissions of hydrocarbons, carbon monoxide and nitrogen oxides from motor vehicles, therefore, can be seen as a major source not only of climate modification but also of adverse health and other environmental effects resulting from ground level pollution. In addition, tropospheric pollution and climate modification have been found to be directly linked by a variety of mechanisms. To deal with these problems in a co-ordinated manner requires the minimisation of carbon monoxide, carbon dioxide, hydrocarbons, nitrogen oxides and chlorofluorocarbons.
On a global scale, total emissions of these pollutants depend on the number of vehicles in use and their emission rates. In turn, their actual emissions rates depend on their fuel efficiency and their use of available control technologies.
Vehicle pollution control devices and fuel efficiency improvements can reduce the greenhouse and other adverse effects which result from these vehicles. However, the continued growth both in the number of vehicles and their use can overwhelm the potential benefits of these technological gains. Unless this growth is constrained, global pollution will continue to increase, many areas which currently have relatively clean environments will deteriorate, and the few areas which have made progress will see some of these gains eroded.
A larger population and greater economic activity in the future holds the potential to increase the problem. Whereas the number of people in Europe and the U.S.A. is growing slowly, the global population is expected to double (compared to 1960 levels) by the year 2000, driven by more than a doubling in Asia and an almost 150 per cent increase in South America, see Figure 2. As well as the overall growth in population, an increasing portion of the people in Asia and South America are moving to cities, thus further increasing the global urban population, see Figure 3. One result is that global automobile production and use are projected to continue to grow substantially over the next several decades.
The next sections will examine both the historical and likely future prospects for the number of vehicles and their use.
World Motor Vehicle Registrations
Overall Historical Trends
The overall trends in vehicle registrations around the world since 1930 are shown in Figure 4. Since 1950, the average annual growth rate for cars has been 5.9 per cent; for trucks and buses, it has been only slightly less at 5.6 per cent per year. Most recently the trends have remained quite high, but the number of commercial vehicles has actually risen more rapidly than cars. For example, since 1970, annual car growth has averaged 4.7 per cent per year while truck and bus registrations averaged 5.1 per cent per year. Overall, as a result of this growth, the total worldwide vehicle count in 1985 was just under 500 million, with the number of cars approaching 400 million.
Recent Trends in Various Areas
With regard to the global car population, Figure 5 shows that Europe and North America each have slightly more than one third of the world’s total, with the remainder divided between Asia, South America, Oceania and Africa, in that order. With regard to trucks and buses, on the other hand, North America has about 40 per cent followed closely by Asia and then Europe.
It seems important to emphasise the dominant role of North America and Western Europe as potential vehicle markets. While the percentage growth in vehicle production is quite high in other countries, and to a lesser extent the percentage growth in vehicle registrations in those countries is also relatively large, the “highly industrialised” Western markets are so big that they dominate the world, and they are likely to continue to do so for the foreseeable future.
The result of this is that, to a large extent, vehicle specifications in these highly industrialised countries will have a significant impact on vehicle characteristics in other areas. For example, it seems likely that increased stringency of emissions or fuel economy requirements in the highly industrialised West would lead to similar requirements in other vehicle markets, especially those where vehicle production is increasing with a view to exporting to the highly industrialised markets. The converse, of course, is also true—weak requirements in the highly industrialised areas will probably result in weak controls in the developing areas. It also appears that much of the vehicle population growth in some rapidly industrialising, developing countries comes from imports of used vehicles from highly industrialised areas. Thus, fundamental designs which are either high or low in emissions or fuel consumption are perpetuated, and can increase or decrease overall emissions and fuel consumption in these rapidly industrialising countries.
Vehicle Registrations Per Capita
As the above figures showed, the number of vehicles in the world has been growing faster than the population. Over the last decade the per capita car population has increased in every corner of the world. This is illustrated in Figure 6, which shows the trends for selected countries and Western Europe. Even the U.S.A., which already has a much greater per capita vehicle population by far than any other area of the world, continues to increase, indicating that there is not a natural limit, or at least that it has not yet been reached.
Projections of vehicle population and use have been developed based on historical trends, patterns of population, and discussions with experts in various countries (39–75). Such projections are, of course, inherently uncertain because of the inability to predict factors such as international crises, prolonged economic downturns, and oil embargoes.
Two methodologies have been used to project the future vehicle fleet. Conservatively, vehicle growth can be expected to follow historical trends, as reflected by a straight linear regression. As shown in Figure 7, this indicates a global vehicle population approaching one thousand million by the year 2030. If, on the other hand, per capita trends are regressed, and then multiplied by population estimates, the global vehicle population would tend to be even higher, as shown in Figure 8. Overall each scenario indicates that the global vehicle populations will increase at an average rate of about 2.5 per cent per year, over the timeframe investigated; in individual countries, particularly in Asia and Latin America, vehicle numbers are growing at an even faster rate.
Possible Limits To Growth
It is important to emhasise that making predictions forty or fifty years into the future is fraught with uncertainty. Will war or economic crises intervene? How will individuals react to increased congestion and pollution? When will the world really run out of economically usable oil?
It seems virtually certain that one or another of these or many other potential eventualities will intervene at some time in the future. However, with the possible exception of World War II, none of the events of the last fifty years has slowed the steady increase in the global vehicle population. For example, some would argue that future vehicle growth will be constrained by the increased congestion which would inevitably result. However, past experience in the U.S.A. has not borne this out. This is well illustrated by the recent events in New York City, as summarised in the article, “New York Rush Hours Grow Earlier and Later”, (76). Most people would agree that during the morning and evening rush hours, Manhattan is one of the most congested urban centres in the United States, if not the world. Data shows that in spite of the congestion, peak hour traffic into and out of Manhattan has increased about one per cent per year from 1981 to 1986; further, it has increased at a much higher rate during the early morning hours and late evening hours, just before and after the peaks. Congestion appears to spread traffic out over a larger area and for a longer time, rather than to stop its growth. As a result, the New York Metropolitan Area continues to grow.
Projecting Total Mobile Source Emissions
Mobile 3 Emissions Model
In the 1970s the U.S. Environmental Protection Agency developed a computer modelling system for predicting the effect of improvements in emission control on motor vehicles. The model used data from tests performed on vehicles taken at random from the in-use fleet to assess the effectiveness of the control technology. This model has undergone a number of significant changes over the last ten years to account for innovations in technology, improved understanding of the emissions process, and changes in assumption about the in-use fleet composition.
Based on available data from sources in various countries, emissions factors for vehicles were developed and used to customise the model known as Mobile 3. This was then used to calculate overall emissions under appropriate driving conditions for each case study.
The emissions rates from the modified Mobile 3 were combined with the vehicle growth projections to estimate future emissions by year. To carry out the calculations, the world vehicle population was subdivided into several vehicle categories according to the level of emission control which was judged likely to apply at a given point in time:
Stockholm Group standards
Common Market standards
East Europe standards
Gulf Coast Council
Vehicles in the first category are assumed to meet the currently adopted U.S. standards, or the approximate technological equivalent, for all categories of vehicles. The second group, the Stockholm group has U.S. standards for cars but somewhat more lenient requirements for heavy duty vehicles. In the third case, all vehicles are assumed to adopt the Common Market standards for all vehicle categories; the so called Luxembourg standards were assumed to go into effect on time in all Common Market countries and with small cars (with engines less than 1.4 litres in size) meeting the same standards as medium sized cars. Eastern Block countries are assumed to adopt the same standards as the Common Market but with a three year delay. The Gulf Coast countries were assumed to adopt U.S. vehicle standards but with a delay until 1995. The final category is self explanatory.
It should be clear from the above summary that there are two different sets of requirements in the world today. First, the U.S. type, which effectively results in the use of three-way catalysts, using primarily platinum, palladium and rhodium, with closed loop electronic feed back systems for gasoline fuelled light duty vehicles. These requirements, giving rise to so called environmentally friendly vehicles, have been adopted by several countries around the world. Secondly, the Common Market requirements (“mixed”) which are much less effective at present but appear to be rapidly approaching U.S. catalyst technology.
Global Carbon Monoxide, Hydrocarbons and Nitrogen Oxides Emissions Projections
Results for carbon monoxide, hydrocarbons and nitrogen oxides are summarised in the three parts of Figure 11. They show that all three pollutants are likely to increase in the future, despite the adoption of all the restrictions that were planned during early 1989⋆. Even these estimates are optimistic because they do not account for the increased emissions likely to occur as a result of increased traffic congestion.
An additional scenario was also added which assumed that by the year 2030, all vehicles around the world would be equipped with the same state-of-the-art—including platinum based catalytic converters—emission controls as installed on vehicles in the U.S.A. These results, displayed on the three parts of Figure 11, show that this alternative has the potential to offset the global vehicle population growth. In other words, if it were possible to introduce state-of-the-art emissions controls across the entire planet, it might be possible to start to reduce global emissions of carbon monoxide, hydrocarbons and nitrogen oxides from the vehicle population, simultaneously absorbing approximately 2 per cent annual growth in vehicle miles travelled.
As noted earlier, climate modifications can result from vehicle emissions other than carbon monoxide, hydrocarbons and nitrogen oxides. Other important pollutants include carbon dioxide, the subject of the next two sections.
Fuel Consumption and Carbon Dioxide Emissions
Fuel Consumption Worldwide
The degree of control of fuel consumption exercised by Governments varies throughout the world. In the U.S.A. and Japan, improvements in fuel consumption are being enforced. In Europe, government control is limited to mandatory publication of vehicle fuel consumption data in only France and the United Kingdom; additionally, voluntary commitments have been made by motor manufacturers in several countries for improvements in fuel consumption. Other measures which have been taken by some countries to reduce fuel consumption include lower speed limits, and higher taxes on vehicles with high fuel consumption.
The U.S.A. Fuel Consumption Experience
It is shown in Figure 12 that automobile corporate average fuel economy figure (C.A.F.E.) rose during the 1970s but has remained fairly flat since the early 1980s. It is important to note that during the 1970s when emissions standards were substantially tightened, average miles per gallon improved significantly. This observation is true even if fuel economy improvements due to vehicle weight reductions are not included. However, during the 1980s when vehicle emission standards have generally stabilised, fuel economy gains have been minimal. Further, without the stimulus of regulatory requirements or market incentives due to higher fuel prices, manufacturers quickly reverted to historical patterns of competing on the basis of horsepower and acceleration rather than on fuel economy or emissions. The lesson seems to be that, just as with emissions, stringent regulation is the surest path to the desired goal.
On a worldwide basis very little if any fuel efficiency improvement is occurring at present. The governmental push of the late 1970s and early 1980s has stalled, and market competition now appears to be focused primarily on performance improvements rather than fuel economy gains.
The significance of this for global carbon dioxide is illustrated in Figure 13. In effect, even with only a 2 per cent annual growth worldwide in vehicle miles travelled, motor vehicle carbon dioxide emissions will drastically increase over the next forty to fifty years. Modest efficiency improvements on the scale of one per cent per annum would barely reduce this growth.
Emissions of hydrocarbons, carbon monoxide and nitrogen oxides from motor vehicles are a major source of climate modification, as well as of adverse health and other environmental effects resulting from ground level pollution. In addition, tropospheric pollution and climate modification have been found to be directly linked by a variety of mechanisms. To deal with these problems in a co-ordinated fashion requires the minimisation of carbon monoxide, carbon dioxide, hydrocarbons, nitrogen oxides and also chlorofluorocarbons.
On a global scale, total emissions of these pollutants depend on the number of vehicles in use and their emissions rates. In turn, actual vehicle emissions rates depend on their fuel efficiency and their use of available control technologies, such as platinum based catalytic converters.
Vehicle pollution controls and fuel efficiency improvements can reduce the greenhouse and other adverse effects which result from these vehicles.
The damage caused by vehicular pollutants is no longer doubted and is increasing on a global basis. Increases in the number of vehicles and the number of vehicle miles travelled is overwhelming the reductions which have been achieved to date, although almost fifty per cent of all new cars produced this year around the world are equipped with state-of-the-art, including catalytic converters, emissions controls.
The Common Market countries of Europe have stood out as the slowest industrialised area to implement state-of-the-art, including catalytic converters, requirements. Accepting that further damage to the environment would result from weak motor vehicle emissions requirements, the Common Market countries of Europe have now agreed to substantially tighten standards. Depending on the resolution of such issues as the incorporation of high speed driving conditions and in-use durability requirements, the overall degree of control could approximate that in the U.S.A. Adoption of the most advanced emissions controls throughout the U.S.A. and Europe, coupled with enhanced inspection and maintenance programmes to maximise the effectiveness of these controls, has the potential to substantially lower carbon monoxide, hydrocarbons and nitrogen oxides emissions in these areas compared to the situation that would otherwise result. If these controls could be applied to all vehicles throughout the world, the projected growth of global emissions of these pollutants would be restrained, at least throughout the first quarter of the next century.
Experience gained during the 1970s and 1980s in the U.S.A. and Japan suggests that the dual goals of low emissions of carbon monoxide, hydrocarbons and nitrogen oxides, and improved energy efficiency (and therefore lower carbon dioxide) are not only compatible but are mutually reinforcing. However, significant gains in either area are dependent on forceful government requirements. Mandatory fuel efficiency standards throughout the world are feasible and necessary to slow the growth in carbon dioxide emissions. In conjunction with stringent carbon monoxide, hydrocarbons and nitrogen oxides requirements, the potential exists to offset not only the global impacts of expected vehicle growth over the next half century but also to start to reduce emissions.
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⋆ As this article was going to press, in a dramatic reversal, the European Council of Environmental Ministers decided to significantly strengthen the Luxembourg compromise. Details are still being developed regarding such questions as incorporation of high speed driving conditions and in-use durability requirements. Depending on how these issues are resolved, the overall emission control of carbon monoxide, hydrocarbons and nitrogen oxides from cars in the Common Market could approximate to that in the United States. In any event, it appears likely that platinum-based three-way catalytic converters will be used on most, if not all, new cars in the European Community by the year 1993.