could be a leaking oilpan .the wind blows the smoke away while driving and when you slow down it goes away leaving the smell. http://www.autozone.com/servlet/UiBroker?UseCase=S001&UserAction=viewSimpleDiagInfo&Parameters=info
Cause its burnt.
Acrid
That depends on the exit, in most cases yes you would slow down when exiting a highway, but there are off-ramps that are mostly straight and lead to another highway.
If you locked your wheels and slid, you burnt your tires and that will smell like burnt oil, since they ARE petroleum products.
Smell is an important part of our lives. Without it, we wouldn't be able to smell fires, for example. That would cause many areas to be burnt down.
The smell of cannabis is quite pungent, reminds me of a mixture of wet soil and burnt pine needles. Probably would smell different for each person.
Giant explosion occurs leaving only the smell of burnt pubic hair.
Brown fluid = burnt fluid (either dark brown or black in color) . In the early stages of slipping, a burnt smell will be the first noticeable indication.
There is a short in your wiring somewhere to your radio. I would check it out. Or get it checked.
That is almost always an indication of a failed transmission. Check the fluid for a burnt smell.
The main part of diesel fuel is kerosene, which produces thick black smoke, and gives that smell that is commonly associated with diesel. most likely if it is white smoke, it is antifreeze, if it has a blue tint to it, it is oil. the smell of burnt diesel is rather strong so it could cancel the burnt oil smell, or on the other hand it could be coolant, because burned coolant doesn't have a strong smell. I would check your coolant and oil levels, and check your coolant for having oil in it.
Many things can cause a burning smell under the hood of your car, if the smell is accompanied by smoke you are most likely looking at a fluid leak dripping onto something hot and burning off. If it smells sweet this would be a sign of a coolant leak. A ozone type smell would most likely be caused by a burnt clutch (standard transmission) or brakes hanging up and staying applied. burnt clutch smell would be expected if you have a new driver learning to drive a stick. An exhaust leak would smell, well, quite frankly like exhaust which is a dangerous gas to be inhaling (CO2, CO, etc). either way if your car is smelling funky you should really have a professional auto technician check it out to prevent damage to your health, the environment or future damage to your vehicle.