Dust particles at the mesopause tend to deplete the ionization by more or less sequentially capturing the positive ions and electrons. They remain negatively charged, despite photoelectric emission. For a given radius a the charge on a dust particle may be assumed to be a unique number, or, more rigorously, it may be specified by a distribution function characterized by a mean charge. The latter approach improves the ion depletion rate by ≲15%. The depletion rate coefficient D (cm3 s-1) is calculated to be ?6.5¿10-6 (a=3.16¿10-6 cm), ?4.5¿10-5) and ?3.5¿10-4 (a=3.16¿10-5). Dust plays an important but not a dominant role in governing the ionization at the mesopause: for Nd>1 cm-3 and a>1005 cm it may be a dominant constituent.