[no1_vern]

I had no idea that Urea could be used to "scrub" diesel exhaust.

Quote:

Urea tanks on diesel trucks -- that's the law in the United States starting in 2010
Automotive grade of world's most widely used nitrogen fertilizer used to meet new US environmental regulations to cut air pollution.

Urea tanks will be standard equipment for most new diesel trucks, buses, cars, and sport utility vehicles (SUVs) manufactured in the United States after Jan. 1, 2010. An automotive grade of urea will be injected into the vehicles' exhaust stream to "scrub" nitrogen oxide (NOx) from the diesel exhaust.

NOx, a major air pollutant, contributes to smog, which causes asthma and respiratory and heart diseases.

Apparently they will be required to shut down if they run dry of Urea- New diesels won't run when the urea tanks is dry - Autoblog

Quote:

Owners of the new crop of clean diesels will have another maintenance item to concern themselves with if their new cars are equipped with urea injection. The EPA requires that all diesels meet strict new emissions standards, which almost always requires the use of either a NOx trap or urea injection. To ensure that the system is working, a sensor checks both the level and the quality of the urea solution and will keep the car from starting if the tank is empty.