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Introduction See my experience with a hybrid car hereIntroductionWithout doubt, light road vehicles are a major source of pollution today. These include the pick-ups and 4x4 SUVs, so beloved by many in various countries to take their kids to school or for going to the mall. Even in countries where annual testing is mandatory, some of them can be seen on the roads, spewing clouds of smoke from their exhaust pipes. This is certainly increasing local pollution levels and could be stopped overnight by strong action. However, this is only a small part of the problem. There are seven types of polluting emissions coming from cars, even as they are driven away from the showroom, with an eighth type on cars which burn petrol (gasoline) containing lead in those countries where it is still permitted:
As a general rule, the larger the car, the higher is the amount of pollution produced. For this reason, I suggest that, for passenger use, it is unnecessary to have cars with engines larger than, say, 2 litres capacity in countries where the speed limit on motorways is 130 km/h or less. Petrol (gasoline) or diesel?In my opinion, only petrol-driven cars with a catalytic converter should be used for passenger use. It is true that diesel-engined cars consume less fuel per 100 km than their petrol-driven counterparts, of equivalent power, even though they may have slightly larger engines. However, this is no advantage in terms of pollution. The amount of carbon in diesel fuel is higher than in the more volatile petrol, so that the carbon dioxide produced is substantially equal (typically 150 - 450 g eq. C/km, depending on engine size and other factors). All the other of the first six pollutants in the above list are higher with diesels than with petrol-engined vehicles fitted with a catalytic converter, even if the diesel burns desulfurised fuel and is fitted with a particle filter, which is effective only for the larger particles. That having been said, some of the latest diesel engines have become less polluting than earlier ones, provided they are correctly maintained. However, the advantage of this is reduced as the wear on the engine components increases, typically after having run 75,000 - 100,000 km. The big advantage of diesel cars used to be the very considerably lower cost of diesel fuel. However, this advantage has diminished and is expected to do so even more in the future. In many EU countries, the cost of diesel fuel is either the same as petrol or even higher, in attempts to reduce pollution. 2-WD or 4-WD?I address a question to owners of 4-WD vehicles: when was the last time that having all-round traction allowed you to get out of a difficulty that would have been impossible with a conventional passenger car? I wouldn't mind betting that a large majority of non-agricultural owners, if they were honest, would answer years ago. Even in winter, with snow, 4-WD may occasionally be helpful, but special snow tyres on a 2-WD vehicle are more effective than ordinary ones on a 4-WD. Furthermore, steering and braking control on a 4-WD are worse than on a 2-WD under snow or icy conditions. So, why have this feature which adds heavily to the cost of a car and adds to the weight and therefore the fuel consumption? Catalytic converter?What is a converter? Such a system meters some air into the exhaust gases before they go into the converter. This is a container containing thousand of ceramic beads or ceramic nets, each coated with a microscopically thin layer of platinum. As the hot exhaust gases hit the platinum, the latter reacts chemically with them, without being consumed, and this reaction is what is called exothermic, which means that the temperature rises. In fact, it reaches a bright red heat and this allows any residual combustible material in the gases to be burnt. The result is considerably reduced emissions of carbon monoxide, VOCs, NOxs, heavy hydrocarbons, sulfur compounds, etc., all of them pollutants. It should be noted that converters do not reduce carbon dioxide emissions, another pollutant. There is one proviso with converters; if leaded petrol is used, even in minute quantities, the platinum becomes "poisoned". One tankful of leaded petrol will stop a converter from working, for ever. It is quite an expensive component to replace, but this cost would have to be borne by the careless motorist, because the annual exhaust test will reveal the problem. It is for this reason that the filler tubes of cars with converters have a diaphragm which will not allow the filling nozzle of a leaded petrol pump to enter. Diesel cars cannot be fitted with catalytic converters and this is one of the reasons why they are more polluting. The only filtration is capturing and burning particles greater than about 1 µm diameter; smaller particles, which are the most dangerous as they remain suspended in the air longest, pass through unaltered. PollutionLet's have a look at the pollutants in the above list. Carbon oxidesCarbon dioxide is the major cause of global climate change (see the essay on Climate change). Signatories of the Kyoto Protocol and other agreements have a legal obligation to minimise emissions of carbon dioxide. Reducing these may involve:
Carbon monoxide, which is a highly toxic gas causing semi-chronic cumulative damage to the oxygen-carrying capacity of the blood, oxidises in the air to carbon dioxide within a day or two, depending on the abundance of hydroxyl radicals. Carbon monoxide is burnt in catalytic converters and little is emitted from vehicles thus fitted. Volatile organic compounds (VOCs)VOCs are organic gases or vapours. Typically, in this context, they are vapours or decomposition products derived from unburnt or partially burnt fuel. Their effect is essentially local and they are a component, along with NOxs, of the smog, haze and ozone that affects most towns, especially in summer. Anyone having seen the pollution in Cairo, Delhi, Bangkok, Mexico City or a host of other cities will know the problem. This is largely due to motor traffic. The mechanism is a chemical reaction between the VOCs and the NOxs, triggered by sunlight. The resultant reaction is also the precursor of a second photochemical one, which produces ozone, a highly toxic and irritant gas when it is at ground level. It requires only trace amounts to cause a reduction of immune system responses and this is the probable cause of a number of diseases, including asthma in children. There are some natural producers of VOCs, such as terpenes and terpenoids emitted by a few aromatic plant species. The quantities in cities from these sources are negligible. On the other hand, in forested areas, natural VOCs may approach similar levels to those produced by vehicles. Nitrogen oxides (NOxs)There are several different kinds of nitrogen oxides. The only normal major natural source is the reaction between the nitrogen and oxygen due to the heating effect of lightning strikes. Most of this is immediately washed out by rain. All combustion at temperatures exceeding about 500°C will produce NOxs and that in the cylinders of a car engine is no exception. This is the other component, with VOCs, required to produce smog, haze and ozone, especially in cities (see the preceding section). Diesel engines, even with particle filters, produce more than petrol engines with a catalytic converter. Heavy hydrocarbonsThis is a phenomenon normally associated principally with diesel engines, although it does occur, to a small extent, in petrol engines, especially if badly maintained. Unburnt fuel, in contact with the cooled cylinder walls, and oil which passes the piston rings and valve guides, often undergoes a number of reactions because of the heat and pressure. These often produce polymers of the alkane groups and other heavy hydrocarbons, as well as VOCs. Many of these heavy molecules are dangerous to lung tissue and some may even be carcinogenic (causing cancers). Even if you cannot see exhaust gases, these heavy hydrocarbons are inevitably produced. If the exhaust is actually visible, then the problem is severe. More HCs are produced during starting and acceleration than in running a hot engine. Sulfur compoundsAll fossil fuels contain sulfur compounds. These are mostly removed during refining, especially the specially desulfurised fuels, but there is always a small proportion remaining. These produce sulfur dioxide during combustion and this oxidises in the air to form sulfur trioxide. This combines with humidity to form sulfuric acid, a major component of "acid rain". This can cause various illnesses in plant and animal life, including a contribution to emphysema and asthma in humans. It also causes attack of the surfaces of marble and limestone (e.g., the problems with the Parthenon in Athens) and, when it does so, it releases carbon dioxide, increasing the atmospheric loading. It is also believed that sulfuric acid, resulting from the combustion of fossil fuels, was a major contributor to the deaths of some 4,000 persons during the smog in London in December 1952. Particulate matter from exhaustsAll vehicles emit particulate matter, such as tarry soots. These have been identified as probable carcinogens (similar to those produced by cigarette smoking). With cars fitted with catalytic converters, most of this particulate matter, with a well maintained engine, is burnt, except that the converter does not start to work until it becomes hot, usually after 5 or 6 km after starting from cold. This is also when the engine runs "rich" (i.e., with a higher fuel-to-air ratio), so that the combustion is incomplete and most soot is formed. A car with a converter is just as polluting as one without a converter in these first few kilometres. Diesel engines tend to produce more particulate matter than petrol engines and cars, of all types, with a high oil consumption especially so. The particles can be wind-borne over considerable distances, especially in dry conditions. Particulate matter from friction between tyres and road surfacesThis is an inevitable part of road transport. We all know that a tyre wears down its tread at a rate of (very roughly) 1 mm/5,000 km, depending on the car, the tyre composition, the air pressure, the way it is driven and so on. This represents between 150 and 250 g of rubber compounds per tyre. For every 1,000,000 private vehicles running 15,000 km/year, on average, it means that about 2,500 tonnes of rubber compounds are lost each year. Most of this is transformed into dust and such dust cannot be healthy, even if it is inevitable. At the same time, the road surfaces are worn, probably to a similar degree. Most of the surfaces are made from compacted hot melt petroleum bitumen aggregate (usually referred to, incorrectly, as asphalt). The bitumen is formed from the still bottoms after the refining of petroleum and consists of an unrefined mixture of many heavy hydrocarbons and carbon. Almost certainly, some of these hydrocarbons are suspected carcinogens. The quantity of bitumen converted to dust is unknown. Lead compoundsTetraethyl lead (TEL) has been added to petrol to prevent "knocking" in engines since about 1923. This allows the compression ratio of the engines to be increased, thereby obtaining a better efficiency without premature ignition and thus damage to the engine. The quantity of TEL added to petrol was small, up to 0.8 cm3 per litre, but the total quantities of petrol sold are enormous, leading to an annual consumption of thousands of tonnes of the substance. Most of the lead passed through to the exhaust in a variety of compounds, some as gases, some as dust. Lead compounds are very toxic to humans and cause a variety of health problems. In particular, the brain and intellectual development of children is severely retarded when they are constantly exposed to lead compounds. It has been found that the lead content in the blood of children has been reduced by more than 75% in children in the USA since the sale of leaded petrol was banned. For the anecdote, the man who discovered that TEL reduced "knocking", Thomas Midgeley, a mechanical engineer with no knowledge of chemistry, was also the same person who discovered CFCs, used in refrigerators, causing depletion of the ozone layer; this one man had on his shoulders the responsibility for two major and potentially dangerous environmental hazards! Unfortunately, leaded petrol is still on sale in many countries, even though its bad effects have been known for over 30 years. This does nothing for anyone and I urge everyone, in the strongest terms, never to use anything but lead-free fuel. If their car is old and will not accept it, then the engine should be modified to allow it to be used (or taken off the road!). It was an anomaly that leaded petrol is still on sale, when it has been banned for many years in most developed nations and many developing ones. Environmentally-acceptable carsConventional carsIt is acknowledged that the private car is a must for most families who have economic access to one. However, the present mindset of buying the biggest and most luxurious car, to impress the neighbours, is little short of irresponsible. A small to medium-sized petrol car with catalytic converter is cheaper to buy, to tax, to insure, to run, causes less pollution and is every bit as comfortable for the lengths of trips usually undertaken - and it is still just as easy to be caught in a radar trap! As I said earlier, anything over 2 litres for an ordinary 5-seater family car is wasteful and, if local conditions dictate that you must have 4-WD, there is still a choice of good ones at this level. There is prestige to be gained by showing people that you prefer an environmentally responsible vehicle, rather than a de-luxe limousine or a sports car. Electric carsThere are no electric cars generally available or suitable. In any case, if there were a large fleet of them, they would have to be charged from the electricity supply, which is not dimensioned for such a load, and which usually burns fossil fuels, in any case. They are not environmentally acceptable. Wide-scale trials in California have shown that electric cars are not acceptable to the public either; owners of them rarely renew their vehicles with another electric vehicle and many stop using them within a matter of months, they are so inconvenient. Petrol-electric hybrid carsIt is disappointing that the hybrid car is not more widely available. There are several models, from small coupés to medium saloon cars to people carriers, and even, believe it or not, SUVs, made in mass production with typical consumptions of 4 to 6 l/100 km for the mid-sized ones, less than half that of a comparable conventional car. Most of them come from Japan but production is also starting in the USA and Europe. They have been in production for some years and the technology has been mastered. The American motoring magazine, Motor Trend, mostly directed towards cutting-edge enthusiasts' sports cars, has named a hybrid car its Car of the Year 2004; this link is well worth reading, if only to show the direction that the car is heading. The car in question in this link has a town consumption of only 3.96 l/100 km! This means that its 45 litre tank of lead-free petrol will take you an astounding 1,100 km before you have to refill - all around a crowded city! Because the widespread adoption of such cars would help solve various countries' commitments towards reducing carbon dioxide emissions, there are various subsidies or tax relief available for owners in some places. It may be useful to note that the consumption of some hybrid cars under fast highway conditions is higher than under urban driving. This is the opposite of conventional cars. I watched a TV review of the Toyota Prius recently and the reviewer, Jeremy Clarkson, complained that the consumption was too high, judging from a single fast return trip from Oxford to London on the M4 motorway. This was unfair, because the car was not meant for that. He then went on to say that he could get a better consumption with a small diesel, I think a VW Fox 1.4 l TDI. This is probably true on a motorway, but there is a lot of difference between an ultra-compact Fox and a mid-sized Prius − and I bet he would see a big difference if he had to cross London from the M4 to the M2 motorways. A more honest appraisal may be seen at this comparison between a VW Jetta diesel and a Toyota Prius. A French car-producing conglomerate (Citroen-Peugeot) has recently started to develop a small diesel-electric hybrid power train. Diesel engines do not lend themselves easily to the concept because of a different torque/power curve and constant starting/stopping of the engine is less suitable. However, prototype figures of about 3 litres/100 km in urban driving are impressive for a compact car. It would seem unlikely that this car will enter into production in the near future, implying that there are still problems to be ironed out. In June 2007, I took delivery of a Honda Civic Hybrid. My experience with it is recounted on a separate web, here. It has met most of my expectations and I have found a number of things that the manufacturers don't say! Vegetable oil cars, bio fuelsTheoretically, the "chip-oil" car could be used in warm climates. This is a standard car with a modified diesel engine designed to use vegetable oils as fuel. The used oil is collected from crisp factories, hotels, restaurants and other sources. It is carefully filtered and refined and then thinned down with a small quantity of kerosene. Of course, it emits just as much pollution as any other diesel car; the difference is that 90 per cent of the fuel is from non-fossil fuel sources and the carbon dioxide is therefore renewable to the same extent. It is uncertain whether the collection, treatment and distribution of used vegetable oil would be commercially viable, because the quantities of raw materials is relatively small and would suffice only for a fraction of the cars on the road. It is unlikely that special non-edible oil-producing crops could complement the availability, at least on a large scale. However, cars with the modified diesel engines can run equally well on conventional diesel fuel, so that the vegetable oil could be used when it was available. In cold climates, it has been found that 10 percent of vegetable oil can be added to conventional diesel fuel without much inconvenience. Petrol cars can be modified to run on light alcohols, such as a mix of methanol, ethanol and propanol. Unfortunately, as a general rule, to make such fuels will require more energy than can be derived from them, although ethanol has been widely used in Brazil. To harvest and transport fuel crops is fuel-intensive and then, after fermentation, distillation of the alcohol requires much energy. Toxicity issues are also a concern, especially with methanol. However, where the alcohol is readily available in an anhydrous condition, up to 10 per cent may be added to conventional petrol without requiring any modification of the engine. However, the fossil fuel savings are less than 10 per cent because ethanol has a lower calorific value per volume than petrol, so more fuel is required under any given running conditions. Unfortunately, edible crops are being used to make biofuels for cars. This has had the effect of reducing the availability of such crops for food and the commodity prices have risen drastically as a result and less food is available for international aid programmes. The selfishness of man in developed countries to run his gas-guzzling car with the "feel-good" factor of using so-called "green" fuels is killing third-world children. This is not acceptable. Cars of the futureNobody can predict the car of the future. The hydrogen-powered fuel-cell car is being much hyped as one possibility, although it is unlikely to be in full production in less than 12 or 15 years from now. Although the protagonists claim that this is the way that private cars will go, there are still many unanswered questions. Some of these issues have been evoked in the essay on Hydrogen. It is shown that it would seem very doubtful whether this type of vehicle would work unless the people accepts the notion of nuclear power stations. However, there are severe doubts as to whether the hydrogen fuel-cell cars will ever become a mainstream solution, because:
In the shorter term, it would certainly be the hybrid car that would offer the best solution. By 2006/2007, there will probably be tens of models with very advanced technology available on the market at attractive prices. Reduction of consumptionOf course, the best way of reducing pollution from cars is not to use them! The first and foremost way is to use public transport. Unfortunately, the public transport system in some countries is almost non-existent and is often totally unco-ordinated. It is an urgent requirement that this be addressed so that anyone in any locality can reliably reach any other locality within a 250 km radius in, say, half-a-day with no more than two changes. This could be co-ordinated with mail delivery. The example of the postal buses in some European countries shows that this can be done with radiating services from hubs which are interconnected by high-speed coaches or rail in some other countries. The crux of the system is that there are always postal buses waiting for the arrival of each train or coach, having delivered passengers from the outlying areas and waiting to take new passengers back there. This would require very radical planning and infrastructure. The important point is that it must be made convenient. It could be done. The idea of a new high-speed rail systems, such as the French TGV, for the transport backbone should not be discounted, either. This would require vision, but it would cost little more than adding an extra lane in each direction to the motorways. Container freight could also be carried, relieving the motorways of their polluting juggernauts. Of course, as I mentioned earlier, walking the kids to school, rather than using the car, as well as light local shopping would be helpful, especially as cars are at their most polluting on short trips. Planning the heavy shopping, such as to the large supermarkets, to go only once every two weeks, requires some forethought. For the daily perishables, use the nearest shop; even if a salad there costs 20 cents when the large shop charges only 15 cents, the difference is equivalent to only a little over a kilometre in a car in one direction, just for the fuel. A heavy carbon tax on motor fuels is necessary. This would bring the price of diesel to over that of lead-free petrol, but it is the only way to discourage people from buying cars with high consumptions and encourage those with low consumptions. The extra fuel cost for families may be compensated by having low road taxes for small, economical, cars, say, $10/year, but high ones for "gas-guzzlers", rising to, say $10,000/year for anything whose fuel consumption exceeds, say, 20 l/100 km, such as Humvees. This could be compensated by tax reductions for proven professional use where a smaller vehicle would be unsuitable. ConclusionIt would be possible to reduce car-engendered pollution, including carbon dioxide emissions, very significantly. This would require a three-pronged approach involving public transport, low-consumption cars (especially hybrids) and public awareness to allow them to use their cars more efficiently. More incentives are required to further these aims and particularly to discourage "gas-guzzlers". Further Reading:Books on environmentally friendly cars |
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