If a specific mass of air is polluted, will the pollution stick with it?
Air is a fluid, as such it tends to mix and concentrations, of anything, tend to disperse into the wider volume. Erik's cup of tea metaphor is pretty accurate, currents of air will pull apart your exemplar 1m3 and disperse the pollutants therein, the heavier particulate, which is mainly soot, water droplets from combustion, and unburned fuel, will full to the ground fairly quickly. Finer particulate and reactive gases like nitrogen and sulfur oxides will react with water to form acids and fall back to earth with the next rain storm. The exception to this general rule of mixing occurs when there is an inversion layer that puts a "lid" on vertical circulation in a particular area causing a build up of pollutants which often results in smog formation.