Diesel exhaust emissions tested

Research reveals new diesel vehicles are getting cleaner with the very latest Euro 6 diesels showing an improvement on Euro 5 of 72%.

“The regulation change to Euro 6 has reduced the permitted levels of NOx by 55% but, in real terms, the very latest Euro 6 diesels that we’ve tested are showing an improvement on Euro 5 of 72%,” explains Nick Molden of Emissions Analytics, a company currently in partnership with Imperial College, studying urban emissions for transport planning and policy.

With over 350 diesel vehicles analysed so far, data reveals the earliest Euro 6 diesels produced levels of NOx significantly above the legislated limits. As reported in the International Council on Clean Transportation’s 2014 report, to which Emissions Analytics contributed data, the average was seven times over the limit.

However, many recent Euro 6 diesels show marked improvement, with NOx levels averaging around 2.5 times the legislation limit of 0.08 g/km.

The introduction of diesel particulate filters for Euro 5 stage went a long way to clean up the solid matter (soot) emitted from the exhaust. However, the levels of nitrogen oxides demonstrate the need or further work required vehicle manufacturers to help improve air quality and reduce the threat to health from diesel exhaust.

Diesel exhaust emissions

Nick Molden concludes: “To claim that all diesels are dirty misrepresents a complex situation. While it is certainly true that older diesel vehicles, including passenger cars, buses, taxis and delivery vehicles are significant contributors to poor air quality, our data shows that, with the introduction of the latest Euro 6 vehicles, the situation is improving. What this shows us is the important role real on-road emissions testing has to play in cleaning up our towns and cities.”

Car exhaust cocktail

Cars emit a complex cocktail of exhaust gases, many of which have harmful effects on both our bodies and the planet. Below are listed some of the major pollutants, along with some of their harmful effects.

Benzene (C6H6)

This naturally occurring hydrocarbon is found in crude oil, and therefore petrol, but is also produced during its refinement and combustion. Although typical atmospheric levels of Benzene are thought not to be harmful, benzene is a carcinogenic substance, and high levels of inhalation can carry severe penalties to human health.

Cadmium (Cd)

This metal naturally occurs in the Earth’s crust, and is released into the air in the form of various cadmium compounds on combustion of petrol and other fossil fuels. Cadmium oxide, one of the main by-products of combustion, is damaging to the lungs and kidneys on inhalation or ingestion, and is thought to be carcinogenic.

Carbon Dioxide (CO₂)

CO₂ is not a health damaging gas at normal atmospheric concentrations, but it is the principal driver of climate change today, and thus, arguably the most dangerous pollutant for mankind today. Did you know, for example, that a 6,000 mile journey travelled by car produces roughly its own weight in CO₂? Transportation is the fastest growing source of CO₂ emissions. The main way to cut these emissions is through reducing our use of fuel, and this can be done by (a) driving less, and (b) using more fuel-efficient cars. You can also help offset the emissions you do create by making your driving carbon neutral.

Carbon Monoxide (CO)

This is a toxic, colourless and odourless gas, produced by the incomplete burning fossil fuels such as coal, oil, petrol and gas. In Britain, road traffic is responsible for over 70% of CO emissions. CO reduces the oxygen carrying capacity of the blood, interfering with the transport of oxygen from the lungs to the tissues (including the brain). It can cause headaches, nausea, fatigue, and at high concentrations, coma and death.

CO also adds to ground level ozone concentrations, combining with other pollutants to form photochemical smog, and is one of the minor anthropogenic gases contributing to climate change.

Nitrogen Oxides (NOx)

There are a number of nitrogen oxides, all of which are produced on combustion of fossil fuels. Not only do they aggravate asthmatic conditions, and react with oxygen in the air to form the irritant ozone, but they are also one of the key causal agents of acid rain. On reacting with atmospheric moisture, they acidify it, and this moisture, when it falls as rain inhibits the growth of plants, is damaging to freshwater and soil life, and is damaging to buildings.

Nitrogen oxides also contribute to photochemical smog. They irritate lungs, and increase susceptibility to viral infections.

The percentage of NO2 in the NOx is an important consideration as NO2 is a major contributor to pollutant-related health issues - the ratio of NO2 to NOx can be as high as 90% in urban driving. A large proportion of NOx is emitted during stop-go urban driving - particularly while a vehicle is accelerating. This is one of the principal contributors towards urban air quality problems, and underlines the importance of looking beyond the headline numbers.

Particulates

Diesel engines emit particulates (or soot), which are increasingly being linked with asthma. Although car manufacturers are attempting to make these particulates smaller (as is now legally required), these micro particulates now penetrate even further into the lungs resulting in less obvious, but longer-term damage. Euro 5 diesels are fitted with filters that remove exhaust particulates.

Some estimates have suggested that particulates are responsible for up to 10,000 premature deaths per year in the UK alone. What’s more, 25% of particulates come from road transport.

Sulphur Dioxide (SO₂)

This is a colourless gas, which smells like burnt matches, and is emitted by both petrol and diesel engines. Along with Nitrogen oxides, SO₂ contributes to acid rain. The gas can also cause breathing problems, aggravate asthma, and worsen both respiratory and cardiovascular disease. It also brings about the formation of acid aerosols, which as well as being highly detrimental to human health, contribute to climate change.

The ethical choice

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