A colloid is a mixture that has particles ranging between 1 and 1000 nanometres in diameter. The phase that is scattered or present in the form of colloidal particles is called the dispersed phase. The medium in which the colloidal particles are dispersed is called the dispersion medium.
The dispersion medium is gas and the dispersed phase is solid. It is an aerosol. Aerosol contains small particles of liquid or solid dispersed in a gas.