I think unless the car is running poorly or there's a diagnostic code there is probably nothing wrong. My 95-850 with 130K gets only a little better mileage than you do. Are you an agressive or easy driver, how much load do you have in the car, and what kind of terrain do you drive on?

I have a Ford Taurus whose size and weight are very similar to the Volvo and has been carefully maintained with no indications or history of fuel or other problems. It runs smoothly, passes emission tests and gives off no exhaust smell except at cold start. At 58K miles, it gets 14 mpg city and 23 highway.

I have the black soot too and was concerned until I looked at the tail pipes of cars where I park at work (Volvos and many others) - every single one has a tail pipe which is black and sooty inside.

When you start the car (cold engine) the fuel mixture is highly enriched. The normal control of the mixture via feedback from the oxygen sensors doesn't go into effect until the car has been running for a minute or so. Until that happens I think the fuel smell is normal - it has been present at startup on various cars I've owned.

If the engine coolant temp sensor is significantly out of spec the car will not run right once it is warm and you will probably see the check engine light.

Regarding the air pump/air injection I am unfamiliar as I do not have this on my car.