Green claims of diesel cars disputed by some experts
Sun 01 May 2011
View all news
Modern diesel cars may not offer the emissions benefit previously thought according to Stanford University's Mark Jacobson and some other experts who say that the soot emissions of diesel cars are now underestimated.
Filter technologies have cleaned up diesel cars traditionally viewed as far more polluting than gasoline rivals and vehicle standards, in any case, often focus on carbon emissions and fuel economy, where diesels perform best.
National incentive schemes to promote carbon reduction do not account for soot, which can also contribute to global warming through a substance called black carbon. The omission is a mistake, according to some analysts.
Even reduced levels of soot could still be the equivalent of an extra one gram (g) of CO2 per kilometer, according to the estimates of two leading experts. Black carbon is produced from incomplete burning of fossil fuels and is blamed for accelerating global warming by soaking up heat from the sun. It can darken snow and ice when it lands, hastening a thaw such as in the Arctic or Himalayas.
Modern diesel cars also produce more NOX emissions than gasoline, which in turn creates a greenhouse gas and pollutant called ozone which can harm the lungs. But NOX emissions also destroy a powerful greenhouse gas called methane, further muddying the net effect of such cars on the environment.
Veerabhadran Ramanathan from the U.S. Scripps Institution of Oceanography, supported Jacobson's calculations.
Other researchers, however, said that it was difficult to compare CO2 with black carbon as they behaved differently, staying in the atmosphere for centuries and just weeks respectively.
"I would not characterise the little black carbon that remains in the emissions (as) still a problem," said the California Air Resources Board's ( CARB's) Alberto Ayala.
Related Links
< Back to news list