The release of pollution from the point of emission into the atmosphere is the emission. Broadly speaking, it is the mass of pollution emitted per unit time, broken down by area.
Processes after the pollutant has been released into the air, e.g. further movement, possibly transformation, is called transmission.
The concentration of an air pollutant above our living space is called immission. It is actually the quality of the air measured in a given area. The air pollution measured above our heads is always less than that measured at the point of emission of the pollution, it is diluted.
Of course, the fate of pollution is not independent of the other elements of the natural environment, but interacts closely with them.