The popularity of diesel vehicles has risen in recent years, as consumers acquaint themselves with the latest generation of cleaner-burning, quieter, smoother and faster diesel cars.
All is not well with diesel cars, however--as Researchers at King's College in London suggest diesels are having a catastrophic effects on general health.
Speaking to The Guardian, professor of environmental health Frank Kelly says that as many as one in four premature pollution-related deaths in the UK are caused by diesel emissions.
UK government figures in 2008 linked 29,000 premature deaths to pollution, and as many as a quarter of those could be diesel-related.
Research centers around particulate matter, microscopic particles of soot, sulfates, silicates and others. These particles are small enough to penetrate far into the lungs and into the bloodstream, causing respiratory problems, cancers and heart disease.
Particulates are caused by incomplete combustion of diesel fuel. This has become less of a problem with cleaner-burning engines in recent years, while mandatory fitment of particulate filters on modern diesel vehicles has reduced these still further.
Half of the particulate matter floating around in London's air is from road transport, and half the vehicles on London's roads are diesel-powered.
Many of those are ageing taxis, buses and goods vehicles.
While the latest Euro 6 emissions regulations in Europe reduce particulate matter to virtually nothing, older vehicles--with poorly maintained filters, or none at all in particularly old vehicles--are responsible for many of the problems.
For London, and other countries around Europe, CO2-based tax systems make diesel vehicles popular choices with drivers, instantly cutting tens or even hundreds of dollars from yearly tax bills.
Other CO2-based systems, such as London's congestion-charging zone, have further encouraged buyers to opt for diesels, dodging the $15 daily fee. That's been overturned recently as a lower CO2 limit has excluded all but plug-in vehicles, but for many the damage may already have been done.
Diesels do still have advantages, of course--their economy, particularly at highway speeds, helps reduce fossil fuel usage, and correspondingly low CO2 helps minimize the greenhouse effect.
Highway use also helps diesel particulate filters to work as they're designed, minimizing the risk of potentially expensive clogging. Urea injection has also cleaned up diesel's game in recent years, helping reduce oxides of nitrogen.
But as Europe's cities choke on diesel dust, it highlights the risk of overlooking deeper pollution problems for "fashionable" CO2-based legislation.