Reduction of CO2, the main greenhouse gas, is a key target for the UK Government. The latest tests have been based on a real world drive cycle and a well-to wheel basis.
Petrol CO2 is 20.3% more than autogas
Diesel CO2 is 1.8% more than autogas
The quality of air in our towns and cities is still a major concern for society with an estimated 24,000 deaths being advanced every year attributed to this issue (Source: government statistics). In London around 90% of pollution is caused by road transport with "Ultra Fine Particles" being the major contributor.
They are mostly carbon particles coated with a cocktail of chemicals, known to the public as PM 10s (smaller than 10 microns). These particles do occur naturally, but the type emitted from engines are believed to be rather more harmful to human health. The smallest are seen to be the most dangerous due to their ability to penetrate deeply into the respiratory system with the smallest of these particles being deposited in the alveolar region. PM 10 particles are associated with health effects including increased risk of heart and lung disease. In addition, they may carry surface-absorbed carcinogenic compounds into the lungs.
The tests on fine particles on the urban emission cycle demonstrates that , diesel vehicles emit up to 120 times more fine particles than autogas.
These are an acidic family of gases. These gases are produced in nature in modest quantities and serve to enrich the soil for plant life. Produced by combustion, in larger quantities, these gases have a very significant effect on air quality.
Nitrogen dioxide has a variety of environmental and health impacts. It is a respiratory irritant, may exacerbate asthma and possibly increase susceptibility to infections. In the presence of sunlight, it reacts with hydrocarbons to produce photochemical pollutants such as ozone. The 12 th August 2003 saw the Daily Telegraph report that summer time smog, a mixture of ozone and other noxious gases, broke health limits at 76 out of 80 monitoring sites in the UK.
In addition, nitrogen oxides convert to nitric acid. This nitric acid is in turn removed from the atmosphere by rain - ACID RAIN.
Petrol NOx is 120% to 180% more than autogas depending on the drive cycle
Diesel NOx is over 2,000% more than autogas for any drive cycle.
In other words one diesel vehicle emits the same NOx as over 20 autogas vehicles
No proven technologies are being introduced in the medium term to reduce the NOx from the diesel vehicles tested.
Autogas does not contain heavy metals (nickel, cadmium, arsenic and mercury) - this is not the case for petrol and diesel.
The sulphur content of Autogas is less than Ultra Low Sulphur Petrol or Ultra Low Sulphur Diesel. The only sulphur contained in autogas is that added as part of the stenching agent (to enable a gas leak to be detected by smell) which is generally less than 25ppm.
Research has shown that benzene is a powerful carcinogen causing many types of cancers, particularly leukaemia. The rise in some types of cancer (particularly in children) has partly been attributed to the rise in levels of Benzene in the atmosphere.
Benzene is an aromatic volatile organic compound (VOC) which is a constituent of petrol (about 2% by volume). The level of benzene in petrol was actually increased when lead was removed. The main sources of benzene in the atmosphere in Europe are the distribution and combustion of petrol. Of these, combustion by petrol vehicles is the single biggest source (70% of total emissions) whilst the refining, distribution and evaporation of petrol from vehicles accounts for approximately a further 10% of total emissions.
Benzene is emitted in vehicle exhaust not only as unburnt fuel but also as a product of the decomposition of other compounds.
It's also worth noting that when you fill your car with petrol, the vapour that comes out of the tank contains a high level of benzene which can then be breathed in. Studies from Sweden have found unexpectedly high levels of leukaemia in petrol-station workers.
Autogas does not contain any benzene
Like benzene, this is a VOC emitted into the atmosphere principally from the combustion of petrol and diesel. Unlike benzene, however, it is not contained in the fuel but is produced by the combustion process. The dominant source of 1,3-butadiene in the atmosphere is the motor vehicle. 1,3 Butadiene is also a known, potent, human carcinogen.
So you may be thinking: "But my car has a catalytic converter which will destroy all these harmful gases" and to a certain extent, that is true. Catalytic converters have substantially reduced the quantities of harmful gases emitted from vehicle exhausts, but they are not 100% efficient. Firstly, they only operate above a certain temperature and for about the first three miles or so they do not work well.
Secondly, their efficiency deteriorates with age. By 40 to 70 thousand miles (depending on whose research you read) many converters are not working at all.
Thirdly, they do not remove all the harmful gases. They do not remove carbon dioxide (CO2) - they actually produce it. They do not remove sulphur or any of the heavy metals and they are not very efficient at removing benzene and 1,3-butadiene.
And finally, very few diesels are fitted with any form of catalytic converter.
So if you are concerned about the harmful emissions from your vehicle, the most practical solution is to convert to Autogas.
The combined air toxics emissions from Autogas vehicles are 90% less than those of petrol and diesel .