I was searching a cool website by the EPA that categorizes various vehicles by their green factor, or by how efficient and clean burning their emissions are. I noticed that no diesel engines were listed among the vehicles and sent a note to ask why. This is the reply I got from the EPA.
The reason why you are having trouble finding diesel vehicles is that there aren’t very many offered for sale in the U.S. Only one Mercedes Benz model and a couple of Volkswagen models have been certified to comply with EPA’s strict emission standards. Even though they may be fuel efficient, diesel vehicles have inherently higher levels of oxides of nitrogen, a lung irritant, and particulate matter, a likely carcinogen. These pollutants are particularly difficult to control in diesels, and most auto manufacturers have chosen not to produce them for sale in the U.S., since they are unable to comply with EPA’s strict “Tier 2” emission standards. Car companies are now working on improving the technology needed to control diesel pollution from vehicles, so we will likely be seeing more models in the next few years.
As they mentioned, there are some that meet the standards, and since they are only comparing gasoline versions, there’s no figures for engines burning biodiesel.
So while diesel engines weren’t that green initially, they are getting better and by burning biodiesel, you can vastly improve their environmental impact, and reduce emissions.