Gas powered leaf blowers are small two stroke engines, you’re smelling oil burning (oil is mixed with gasoline to lubricate, it burns by design), and those engines tend to be jetted to run rich so they don’t burn up too quickly.

Unburned gasoline, unburned oil, burned oil are the extra smells that you don’t get from a lawnmower, which would be four stroke like a car.

Two strokes are also noisier than four. They fire twice as often as four strokes, and for the purposes of a leaf blower, they also rev higher.