[Jessica H (OP)]

If gasoline and diesel are just different in the length of the hydrocarbons, and then why do they smell different?  My hand stinks everytime I pump diesel into my car, but I never had that problem with regular gasoline.

[Geezer]

I actually find diesel a bit less obnoxious than gasoline.

Gasoline evaporates quite quickly, so there is no residue on the pump. Diesel is very "oily" and it does not evaporate much, so it gets all over the gas pump nozzle then onto your hands.

You might wear a pair of gloves or put a paper towel in your hand when you touch the pump.

Of course, you could always move to Oregon or New Jersey where someone else has to pump the diesel for you.  []

[Bored chemist]

It's a good approximation to say that petrol and oil are just hydrocarbons, but it's not entirely true. The process starts with crude oil which also contains sulphur and nitrogen compounds.
During refining some of these get removed but not all of them. Generally diesel engines are less "fussy" about what they burn than petrol ones so the fuel needs to be refined to a higher degree. This also removes lots of the sulphur and nitrogen compounds which contribute a lot of the odour.

Also not all the hydrocarbons are simple straight chains. There are also cyclic and aromatic carbon compounds present. Though these compounds are called "aromatic" they don't always smell nice. Petrol has quite a lot of some of the lighter aromatics and these don't smell too bad. Diesel has relatively more of the heavier aromatics (like naphthalene) which are not very nice.
Of course, all the stuff about what "smells nice" is a matter of opinion anyway.

[Geezer]

I understand the truckers in the US like a high sulphur content in diesel because it helps to lubricate the engine. (It also causes a lot of the nasty soot that comes out the exhaust!)

[chris]

How would sulphur act as a lubricant? What's the chemistry behind that? I can only imagine it would behave as an acid and erode the engine components...

[RD]

Sulfur is not a lubricant in of itself, but it can combine with the nickel  content in many metal alloys to form a low melting point eutectic alloy that can increase lubricity.

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[lghf]

Of course, you could always move to Oregon or New Jersey where someone else has to pump the diesel for you.  []

There is no mandatory full service in Oregon and New Jersey for diesel.