α-Hydroxyalkyl-hydroperoxides (α-HHs), from the addition of water to Criegee intermediates in the ozonolysis of olefins, are reactive components of organic aerosols. Assessing the fate of α-HHs in such media requires information on the rates and products of their reactions in aqueous organic matrices. This information, however, is unavailable due to the lack of analytical techniques for the detection and identification of labile α-HHs. Here, we report the mass spectrometric detection (as Cl- adducts) of the α-HH produced in the ozonolysis of a C_(15) diolefin in water (W):acetonitrile (AN) mixtures of variable composition. α-HH decays into a gem-diol + H_2O_2 in τ_(1/e) ~ 52 min in 50% (v:v) water, but persists longer than a day in < 10% water mixtures. The strong non-linear dependence of τ_(1/e) on water content reveals that water content is a major factor controlling the fate of α-HHs in atmospheric particles, and suggests that α-HH decomposes while embedded in W_nAN_m clusters rather than randomly dissolved in molecularly homogeneous W:AN mixtures
