An average car releases 2.2kg of carbon for each litre of petrol burned.
I can't follow that. A litre of fuel weighs about 800g of which I guess about 660g is carbon and most of the rest is hydrogen. Where is the extra ~1.4kg of carbon coming from?
Simplisitically, the C in CO2 comes from the fuel, the O2 comes from the oxygen in the air consumed when the fuel is burned. So 660g of Carbon in the fuel plus 1.54 of Oxygen not in the fuel.