DEF... What's the point?

What is the point of DEF in new trucks? I know that it cleans the exhaust so it is cleaner when it leaves the truck. If people want to crack down on emissions, look at all of the New Yorkers who fly to Washington D.C. every week. One air mile produces 53.3 pounds of CO2. However, semis only produce 6.472 kg per mile. And if people want their food, water, fuel, cars, phones, garbage hauled away, and their houses built, why do they put emissions restrictions on trucks? If the government wants...

DEF... What's the point?

DEF... What's the point?