Why do some brands of green petrol smell different from others

Why do some brands of green petrol smell different from others  

The petrol we buy comprises a mixture of naturally occurring hydrocarbons, a principal component of which is octane but the mixture also contains a small amount of benzene. Some brands of petrol contain more benzene than others, both because of variations in the conditions with which the crude oil is distilled into fractions, and also variations in the reservoir from which the crude oil is obtained. The proportion varies quite widely the average is presently about 3 per cent. 

Petrol containing a lot of benzene smells more strongly of benzene than petrol containing less of it. In fact, the intensity of the smell is in direct proportion to the amount of benzene in the petrol at equilibrium, the pressure of vapour above a liquid mixture 

In the countries of North America, petrol is often called gas, which is short for gasoline.  

If we know the mole fraction of a liquid i (via Equation (5.11)) and the vapour pressures of the pure liquids pf, then we can ascertain the total vapour pressure of the gaseous mixture hovering at equilibrium above the liquid. 

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