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Green Car Guide to Low Emission Cars

A good example of a low emission car is the Nissan Leaf. The one seen here is awaiting a recharge of its batteries. Low emission cars is a term that refers to automobiles that emit less carbon dioxide (CO2) and other emissions such as particulates than the average car – but is that the correct basis on which to judge what is a low emission car?

Over recent years the focus has been on the CO2 emissions that vehicles produce, because a consensus of scientists worldwide agree that high levels of CO2 emissions are having a direct impact on global warming and climate change.

Governments have therefore set policies to reduce CO2 emissions. This has translated to targets for the car industry in Europe to lower the CO2 outputs of their fleets to an average of 130 g/km CO2 per car by 2015. Some manufacturers have already achieved this target. The next European target for manufacturers for average new car emissions is likely to be 95 g/km CO2 by 2020 – this is due to be approved in 2013.

Low emission cars are also more economical than the average car, because there is a direct link between the CO2 emissions of a vehicle and fuel economy.

However there are two significant issues that are currently being debated in the automotive industry concerning what constitutes a low emission car. The first is the quoting of the CO2 emissions from a vehicle’s tailpipe compared to all the other emissions from its tailpipe. The second is quoting the ‘tailpipe’ CO2 emissions compared to the ‘lifetime’ CO2 emissions from a vehicle.

With regard to the first issue, there are other emissions from a vehicle’s tailpipe in addition to CO2. These are often referred to as ‘regulated’ emissions, and include nasties such as particulate matter (PM) or soot, nitrogen oxides (NOx), sulphur oxides and carbon monoxide (CO). Although CO2 emissions are believed to impact upon the planet’s climate, regulated emissions impact upon the air we breathe. This is a very serious issue in cities such as London, where, according to European standards, air quality is very poor.

Low emission cars can help with this problem, as long as they have low levels of regulated emissions. Although diesel cars generally have lower CO2 emissions than equivalent petrol cars, they have higher levels of regulated emissions, especially particulates. In order to comply with future European regulation, diesel engines need to be much cleaner, and this will add considerable complexity and therefore cost to them in the future.

As well as tailpipe emissions, there are ‘whole-life’ CO2 emissions associated with the production of a vehicle. This includes the CO2 involved in the manufacture of a vehicle, in its use, and in its end-of-life disposal. Traditionally the most commonly agreed set of statistics in the industry say that out of the lifetime CO2 impacts of a vehicle , 10% are in its manufacture, 85% are in its use (ie. the fuel it uses during its lifetime), and 5% are in its end-of-life recycling and disposal.

With the increasing number of low, ultra-low, or zero-emission cars, these proportions are changing. Hybrids use less fuel in their lifetime, so that element within the lifecycle is reducing, and the CO2 involved in production and disposal is increasing. This change is even more pronounced with electric cars.

Plug-in Vehicles – Not really zero emission cars

The issue becomes even more complex with the issue of plug-in or electric vehicles. Electric vehicles may be described as low or zero-emission, but they use energy produced by the electricity grid. If recharged using electricity generated by coal-fired power stations in the UK, the emissions from an electric Nissan LEAF can be in the region of 94 g/km CO2, which is higher than the official CO2 emissions from some diesel cars. Ideally, electric cars should be recharged using renewable energy to ensure they are genuine low emission cars.

It is likely that we are heading towards a system where a low emission car will be defined by its whole life emissions, but currently we are far off having sufficiently extensive and standard data to calculate emissions in this way.

More info:

– The Green Car Guide to some of the lowest emission cars currently available in the UK designed primarily for use in the city.

– Some more detail about current green vehicle technologies covering the latest developments in petrol, diesel, hybrid, plug-in hybrid and electric powered cars.

– Which cars have lower whole-life CO2 emissions? – We compare conventional cars with hybrid and electric cars and find out which has the lower overall carbon footprint.