As mentioned above, diesel engines are progressively getting cleaner. This is largely attributed to the usage of particulate filters, of more precise direct-injection technologies and also to the widespread use of ultra-low-sulphur diesel in some countries such as the United States.
But this is not the case in many developing countries. There are still a lot of vehicles, mostly commercial vehicles, in those countries that use old fashioned diesel engines that use pre-chamber type indirect injection. To complicate the matter, the World Health Organization estimates that these vehicles will take a very long time to be replaced with cleaner ones.
Chairman of the working group, Dr. Christopher Portier, explained that the scientific find was rather compelling and the groupís decision was unified; and that diesel engines emissions causes lung cancer in human beings. Portier also mentioned that exposure to this should be reduced worldwide.
The World Health Organizationís working group also looked at exhaust fumes emitted by petrol burning engines but they decided that they were only possibly carcinogenic to humans. This rating hasnít changed since 1989, when petrol exhaust fumes were last evaluated