How vehicles pollute the air
Air pollution from a vehicle's exhaust pipe.
By Gavin Bennet
What you need to know:
- Motor fuels consist of hydrogen and carbon.
Fuels also contain various additives (such as lead, Pb, or other octane improvers etc) and various impurities (such as sulphur).
Which aspect of motoring is the most crucial factor in causing harmful exhaust emissions? Is it the size of the engine, the type of fuel it burns, the owner’s maintenance diligence, the driver’s style, the road conditions, or the traffic volume/density?
Andreas.
All of these factors are interconnected, and they affect both the quantity and quality of exhaust gases, both of which vary considerably for all the reasons you mention.
Quantity: Kenya has a couple of million vehicles in regular use. For every one we have, the wider world has another 600! A total of well over a billion. The quantity of exhaust gas each one generates can be halved — or more than doubled — by the conditions and manner in which it is operated.
Quality: All the elements you mention can cause an even bigger variation between “almost harmless” and “severely toxic and damaging” emissions.
The chemistry: Motor fuels consist of hydrogen (H) and carbon (C). These two elements combine in different molecular structures to create different fuel types (petrol, kerosene, diesel) but all are principally Hydrocarbons (HC). Fuels also contain various additives (such as lead, Pb, or other octane improvers etc) and various impurities (such as sulphur, S).
Most crude oil contains sulphur, which remains an impurity in refined fuels (especially diesel).
Pure air consists mostly of nitrogen (N), oxygen (0) and carbon dioxide (CO2). It also contains various trace gases, and differing amounts of moisture (water, H2O). The action of mixing air and fuel and igniting them causes all these chemicals to react with each other, so the various elements — hydrogen, oxygen, carbon, nitrogen, lead and sulphur — combine in different ways to produce different gases.
Which new chemicals are produced will depend on the ratio of the fuel:air mixture and how evenly and completely the mixture burns when it is ignited.
If the proportions of fuel and air (the mixture) are just right, and the burning process (combustion) is absolutely even and complete, the chemicals produced will be mostly carbon dioxide, water and inert nitrogen oxide. These have no significant ill-effect when emitted by the exhaust and dispersed in the atmosphere.
* Carbon Dioxide: This already exists in abundance in pure air, and is necessary to plant life which absorbs CO2 and converts it into carbons (for growth) and oxygen (which is released back into the atmosphere).
* Water: Water, pure and simple.
* Nitrogen Oxide: There are three main nitrogen oxides — NO, NO2 and N2O. This one, N2O, is inert and harmless.
However, any imbalance in the mixture and any irregular or incomplete burning will produce different chemicals. These include:
* Hydrocarbons, HCs: Unburned or partially burned hydrocarbons (soot/visible smoke). These are foul-smelling and toxic, carcinogenic, acidic when they combine with moisture in the air, and cause photochemical smog. They are poisonous to humans, they irritate and destroy mucous membranes in the body, and they make moist air more corrosive (eg faster rusting of corrugated iron roofs). The colour of unburnt hydrocarbons is black (diesel), grey (petrol) and blue-grey (oil).
Motor vehicle engine.
* Carbon monoxide, CO: When inhaled, this colourless, odourless gas combines with haemoglobin in the blood and reduces the blood's ability to transport oxygen. In low concentrations CO causes drowsiness, nausea and dizziness; in high concentrations it causes death. CO is flammable, and when it burns it generates blue smoke.
* Nitrogen Oxides, NOx: Unlike the inert N2O produced by perfect combustion, incomplete combustion generates NO and NO2, and these are harmful. NO is a colourless and odourless gas, and when it comes into contact with the air it turns into NO2, which is a smelly reddish brown gas which can cause coughing and insomnia. It is also a component of photochemical smog and it dissolves easily in water, producing powerful nitrous (HNO2) and nitric (HNO3) acids. Poor combustion also makes the quantity and chemical composition of additives and impurities worse, involving:
* Sulphur oxides, SOx: Most crude oil contains sulphur, which remains as an impurity in refined fuels (especially diesel). This becomes an exhaust emission of mainly sulphurous gas (SO2), which dissolves easily in water to make foul-smelling, toxic and corrosive substances such as sulphurous acid (H2SO3) or sulphuric acid (H2SO4).
Lead, Pb: This is an additive (now one of many) and is used to increase the octane value of petrol, to prevent knocking (irregular combustion) and therefore reduce emission of HCs, CO and NOx. Both alkyl and ethyl leads are toxic, and can cause cumulative lead poisoning. The alternative octane-enhancers used in so-called "unleaded" fuel are not any less poisonous — they are chosen because lead destroys catalytic converters which help to neutralise CO and NOx emissions.
Many of these toxic compounds have been ameliorated by technology, such as catalytic converters, particulate filters and improved fuel refinement.
Ironically, it is an inherently harmless and indeed life-giving chemical that is an essential part of our atmosphere (carbon dioxide) which is a principal villain in the apocalyptic threat of climate change – purely because we are producing it in such huge quantities that we are changing the natural and essential balance of gases in earth’s atmosphere and causing global warming. The most crucial issue here is not quality. It is quantity.
While motor vehicles make a substantial contribution to this problem, their role is far from predominant. Many other human activities – other forms of transport by land, sea and air; processing; manufacturing; power generation; building construction and use; agriculture; extraction produce many times more.
The bottom line for reducing emissions is to use less HC fuel.
Fuel consumption and emissions are least when the engine (and the rest of the vehicle) is in good condition and driven at moderate and steady speed.
Anything in the road-use environment which compromises that, is doing extra harm.
Which aspect of motoring is the most crucial factor in causing harmful exhaust emissions? Is it the size of the engine, the type of fuel it burns, the owner’s maintenance diligence, the driver’s style, the road conditions, or the traffic volume/density?
Andreas.
All of these factors are inter-connected, and they affect both the quantity and quality of exhaust gases, both of which vary considerably for all the reasons you mention.
Quantity: Kenya has a couple of million vehicles in regular use. For every one we have, the wider world has another 600! A total of well over a billion. The quantity of exhaust gas each one generates can be halved — or more than doubled — by the conditions and manner in which it is operated.
Quality: All the elements you mention can cause an even bigger variation between “almost harmless” and “severely toxic and damaging” emissions.
The chemistry: Motor fuels consist of hydrogen (H) and carbon (C). These two elements combine in different molecular structures to create different fuel types (petrol, kerosene, diesel) but all are principally Hydrocarbons (HC). Fuels also contain various additives (such as lead, Pb, or other octane improvers etc) and various impurities (such as sulphur, S).
Pure air consists mostly of nitrogen (N), oxygen (0) and carbon dioxide (CO2). It also contains various trace gases, and differing amounts of moisture (water, H2O). The action of mixing air and fuel and igniting them causes all these chemicals to react with each other, so the various elements — hydrogen, oxygen, carbon, nitrogen, lead and sulphur — combine in different ways to produce different gases.
Which new chemicals are produced will depend on the ratio of the fuel:air mixture and how evenly and completely the mixture burns when it is ignited.
If the proportions of fuel and air (the mixture) are just right, and the burning process (combustion) is absolutely even and complete, the chemicals produced will be mostly carbon dioxide, water and inert nitrogen oxide. These have no significant ill-effect when emitted by the exhaust and dispersed in the atmosphere.
* Carbon Dioxide: This already exists in abundance in pure air, and is necessary to plant life which absorbs CO2 and converts it into carbons (for growth) and oxygen (which is released back into the atmosphere).
* Water: Water, pure and simple.
* Nitrogen Oxide: There are three main nitrogen oxides — NO, NO2 and N2O. This one, N2O, is inert and harmless.
However, any imbalance in the mixture and any irregular or incomplete burning will produce different chemicals. These include:
* Hydrocarbons, HCs: Unburned or partially burned hydrocarbons (soot/visible smoke). These are foul-smelling and toxic, carcinogenic, acidic when they combine with moisture in the air, and cause photochemical smog. They are poisonous to humans, they irritate and destroy mucous membranes in the body, and they make moist air more corrosive (eg faster rusting of corrugated iron roofs). The colour of unburnt hydrocarbons is black (diesel), grey (petrol) and blue-grey (oil).
* Carbon monoxide, CO: When inhaled, this colourless, odourless gas combines with haemoglobin in the blood and reduces the blood's ability to transport oxygen. In low concentrations CO causes drowsiness, nausea and dizziness; in high concentrations it causes death. CO is flammable, and when it burns it generates blue smoke.
* Nitrogen Oxides, NOx: Unlike the inert N2O produced by perfect combustion, incomplete combustion generates NO and NO2, and these are harmful. NO is a colourless and odourless gas, and when it comes into contact with the air it turns into NO2, which is a smelly reddish brown gas which can cause coughing and insomnia. It is also a component of photochemical smog and it dissolves easily in water, producing powerful nitrous (HNO2) and nitric (HNO3) acids. Poor combustion also makes the quantity and chemical composition of additives and impurities worse, involving:
* Sulphur oxides, SOx: Most crude oil contains sulphur, which remains as an impurity in refined fuels (especially diesel). This becomes an exhaust emission of mainly sulphurous gas (SO2), which dissolves easily in water to make foul-smelling, toxic and corrosive substances such as sulphurous acid (H2SO3) or sulphuric acid (H2SO4).
Lead, Pb: This is an additive (now one of many) and is used to increase the octane value of petrol, to prevent knocking (irregular combustion) and therefore reduce emission of HCs, CO and NOx. Both alkyl and ethyl leads are toxic, and can cause cumulative lead poisoning. The alternative octane-enhancers used in so-called "unleaded" fuel are not any less poisonous — they are chosen because lead destroys catalytic converters which help to neutralise CO and NOx emissions.
Many of these toxic compounds have been ameliorated by technology, such as catalytic converters, particulate filters and improved fuel refinement.
Ironically, it is an inherently harmless and indeed life-giving chemical that is an essential part of our atmosphere (carbon dioxide) which is a principal villain in the apocalyptic threat of climate change – purely because we are producing it in such huge quantities that we are changing the natural and essential balance of gases in earth’s atmosphere and causing global warming. The most crucial issue here is not quality. It is quantity.
While motor vehicles make a substantial contribution to this problem, their role is far from predominant. Many other human activities – other forms of transport by land, sea and air; processing; manufacturing; power generation; building construction and use; agriculture; extraction produce many times more.
The bottom line for reducing emissions is to use less HC fuel.
Fuel consumption and emissions are least when the engine (and the rest of the vehicle) is in good condition and driven at moderate and steady speed.
Anything in the road-use environment which compromises that, is doing extra harm.
Why Safari rally cars are different from the rest
I am told that Safari (and all other WRC) cars only have 1600 cc engines. How come they are so powerful and fast? How good would the drivers be if they used the ordinary cars the rest of us do? Des M
The size of an engine is one determinant of its potential power. There are about 99 other “variable” factors in its materials, design and construction.
Standard cars are designed to be “good” at almost everything – limited construction cost and price, fuel economy, performance, safety, comfort, quietness, long-term durability, flexible usage, simple service, passenger and luggage space, luxury extras, driving ease…etc.
World Rally Championship (WRC) Safari designers start with that base (homologation rules insist on that) but then “modify” just about everything, to produce (very expensively) a car that is sub-standard in many of these respects but superb just at one thing— winning rallies.
Its engine is the same size, but it can suck in twice as much air and fuel and explode it twice as often…at higher compression. It can gain revs (accelerate) twice as fast.
Everything from the shape of the camshaft to the valve springs and gear ratios is different. So is the suspension. So are the brakes. The bodyshell is lighter but stiffer and has a maze of cooling ducts and fans. And so on.
Read: Rebuilding a car in 29 minutes, 30 seconds: First class engineering skills at play in Naivasha
The drivers? The difference between a “good” motorist and WRC elite drivers is bigger than the difference between a person who can play honky tonk on a pub piano, and a person who can play Flight of the bumble bee in a concert hall. If they took you for a drive in your own car, your passenger-seat experience would swing between extreme alarm and disbelief.
How ready are you for wet weather motoring?
The rains are here and I have not got round to checking everything for wet weather and conditions. Should I be worried? Robert D.
Standard cars are well designed for ordinary motoring in wet weather, if they are in all-round good condition. A pre-rains check is simply to reconfirm that condition – not necessarily to add or modify anything.
What you choose to do (or neglect) is as much a personality test as a mechanical task. In psychobabble, we're each of us either more or less introvert or extrovert, anal or oral, pedantic or spontaneous, organised or creative, logical or emotional...etc. In plain speak, each of us is either an accountant, or an engineer or an artist.
The accountants, at this time of year, have already checked their umbrellas (which they carefully dried, cleaned and stored at the end of the last rainy season) to ensure they are still in perfect condition and now strategically placed — a large one by the front door, a medium-size in the boot of the car, and a fold-up one in the briefcase.
The engineers have not done this. But when they open the door one morning to find it's pouring with rain, they'll remember there's an umbrella on their golf bag, find the opening mechanism is jammed, but have a pair of pliers and some WD40 handy to quickly sort it out.
The artists? Well, they'll get wet, having registered the thunderous mood of the sky as “inspiring”, relished the electrical charge and tangy smell in the air of an approaching storm, and in their excitement got as far away as possible from any point of shelter before remembering that they've forgotten to bring a brolly.
For the artist-motorists among you, the only advice there can ever be is “Good luck”. Just remember, or try to remember, that rain makes roads slippery so it's a good idea to slow down a bit and leave a little more room between your bonnet and the next guy's boot.
Oh, and while the drops of rain falling on the windscreen do indeed make some fascinating shapes and colours and movement on the glass, turning on the wipers does enable you to see more clearly where you (and others) are going. A demister fan also improves that.
For the engineer-motorists among you, try an experiment – get ready well in advance this year: check that the tread grooves on your tyres are deep enough to displace four litres of water per second to prevent aquaplaning, ensure your brakes are binding evenly so the car doesn't slew sideways if you have to stop suddenly, put a piece of cloth and some water repellant spray in the glove box (for wiping damp electrics should the car stall), and oil the screwbar on the jack so it's not rusted solid when you need it.
Take a quick squint at the high tension leads from your distributor cap to plugs and coil — if they're cracked or perished you're more likely to have hard-starting and stalling problems. The rubber blades on your wipers should be clean, smooth and supple.
Accountant-motorists should do all the foregoing (in fact, they've probably already done so), and should also ensure the rubber seals round all the lights are sound so water doesn't get at the reflectors, bulbs and wiring inside. They will have checked the rubber bungs under the carpets to ensure they're all in place and won't let water in, and that the drain holes in the doors are not clogged up.
Any residual dust will have been carefully cleaned away before it becomes rust-inducing mud, and not only will the wiper blades have been checked but also the position and spring tension on the wiper arms (to prevent juddering or streaking).
Now is late – but never too late — to do the rounds with oil and grease on moving parts that might get wet and stay wet; and to give the paintwork a protective coat of wax polish.
And, whatever your personality, when the rain is heavy turn on your dipped headlights and spare a thought for pedestrians.
