This manual discusses the capabilities and implementation procedures for MAEROS, the stand-alone multicomponent aerosol module of CONTAIN. The module calculates aerosol composition and mass concentration as a function of particle size and time. The processes that may be incorporated are: (1) coagulation due to Brownian motion, gravity and turbulence; (2) particle deposition due to gravitational settling, diffusion and thermophoresis; (3) particle growth due to condensation of a gas, typically water vapor; and (4) time varying sources of particles of different sizes and chemical compositions. The capabilities of the code are illustrated through simulating an aerosol released in a hypothetical situation.