Junction Triangle

Either way all bad for the Environment, Children and the Vulnerable. However found an article which talks about this very subject:

Diesel Versus Gasoline: Which Is Best For The Climate?
More and more Norwegian cars have diesel engines. Whether these are actually more climate-friendly than gasoline-driven cars depends on which time perspective one emphasizes.

Av Marianne Tronstad Lund

In recent years, the proportion of diesel cars on Norwegian roads has increased. In 2007, 74 percent of new passenger cars had diesel engines, compared to only 48 percent in 2006, according to figures from the Norwegian Road Traffic Information Council (OFV). New tax policies favor diesel cars more and may further stimulate an increase in their proportion. However, it is debatable whether favoring diesel cars is good environmental policy.

A new study at CICERO compares gasoline and diesel engines for the same category of passenger cars within a climate perspective. In the study, the climate effects of the various components in the emissions are calculated so that net climate effects are compared over time. Knowledge gained from this is important in assessing the extent to which substituting gasoline with diesel is helpful in reducing global warming.

Both gasoline and diesel give a net climate warming effect. The study shows that diesel causes more warming than gasoline in the first decade after emission into the atmosphere, while gasoline causes most warming after that period. Which is best depends on your time perspective and what you want to achieve. If you emphasize short-term climate changes or the rate of warming, diesel comes out worse. On the other hand, when the emphasis is on more long-term climate changes, diesel clearly comes out best due to lower CO2 emissions per kilometer driven.
Less CO2 with diesel
The reason for the difference between diesel and gasoline is in the composition of their emissions. We know from before that passenger cars with diesel engines emit, depending on their condition, about 20 percent less of the greenhouse gas carbon dioxide (CO2) per kilometer than the same car type with gasoline engines. However, besides CO2, the exhaust contains a number of other components such as nitrogen oxide (NOx), carbon monoxide (CO), and particles. With the exception of CO, emissions of these components are generally higher from diesel cars, and lead to lower air quality and negative health effects.

But the particles CO and NOx also have important climate effects. The emission of NOx not only contributes to the formation of ozone that has a climate warming effect, but it also reduces the amount of the greenhouse gas methane, which results in a cooling effect. Soot particles from diesel engines absorb solar radiation and cause warming.

The climate effects of the various components work on very different time scales. While CO2 gives a long-term warming effect over several centuries, soot particles and NOx give an intense but short-term warming effect over circa one decade. Warming from diesel, with its higher emissions of the latter components, will therefore be intense right away. On the other hand, with a time perspective of more than 10-15 years where warming from CO2 dominates, gasoline causes greater warming.

New emissions requirements
The study also examines the effect of new requirements for emissions that will be introduced starting from 2009. These stricter emissions requirements will lead to reduced warming, particularly from diesel, and especially during the first few years.

Emissions from road traffic are regulated in the EU by the so-called Euro requirements. These were first introduced in 1993 and have been tightened several times. With the current requirements (Euro 4), higher emissions of NOx and particles are permitted from diesel cars than from gasoline cars. However, this will change with the new requirements (Euro 5) starting from 2009. Emissions requirements of NOx and particles will be tightened, resulting in cleaner diesel cars. Work is also in progress for further tightening of the requirements in 2014 and this will equalize these emissions from diesel and gasoline cars to an even greater extent.

CO2 will become more dominant
CO2 is, however, not included in the Euro requirements but regulated within the EU and EEA region by setting requirements for average CO2 emissions for all new vehicles from each individual manufacturer. With a tightening of requirements for NOx and particles emissions, it is the short, intense warming effect from diesel that will be reduced the most. CO2 will then dominate warming to an even greater extent. As a result, with Euro 5, gasoline is expected to cause more warming than diesel after only 5 years. Because it is the short-lived components that are affected, the regulations will mainly have an effect on warming during the first 10 to 15 years.

Because of the different compositions of emissions and many different climate effects on different time-scales, comparing diesel and gasoline is not straight forward. In addition, the effects on air quality and health have to be taken into consideration. This autumn, the Norwegian Pollution Control Authority (SFT) released a report in which the environmental costs of CO2 emissions are compared with the health-care costs related to air pollution. With the new Euro 5 requirements, the main conclusion is that emissions from new diesel cars give lower net climate, environmental, and health-care costs than emissions from new gasoline cars. However, the climate effects of NOx, CO, VOC and soot particles are not analyzed in the report.
Sources
www.sft.no
www.ssb.no
www.ofv.no
Ingrid Strømme, et al, Miljø- og helsekonsekvenser av utslipp fra bensin- og dieselkjøretøy [Environmental and health consequences of emissions from gasoline and diesel vehicles]. 2008, Norwegian Pollution Control Authority (SFT)
Terje Berntsen, Jan S. Fuglestvedt, and Kristin Rypdal, Climate effects of passenger cars: gasoline versus diesel (in prep.). 2008.