Any of a series of relatively long-lived compounds that sequester more reactive oxides of nitrogen, hydrogen, and halogen in the stratosphere. Examples include 1) chlorine nitrate, ClNO₃, which ties up both ClO and NO₂, and 2) HO₂NO₂, which is a HO₂ and NO₂ reservoir. The presence of these compounds serves to mediate the ability of the more reactive oxides to destroy stratospheric ozone, or to produce tropospheric ozone.