The -hydroxyalkyl-hydroperoxides [R-(H)C(-OH)(-OOH), -HH] produced in the ozonolysis of unsaturated organic compounds may contribute to SOA aging. -HHs inherent instability, however, hampers their detection and a positive assessment of their actual role. Here we report, for the first time, the rates and products of the decomposition of the -HHs generated in the ozonolysis of atmospherically important monoterpenes -pinene (-P), dlimonene (d-L), -terpinene (-Tn) and -terpineol (-Tp) in water:acetonitrile (W:AN) mixtures. We detect -HHs and multifunctional decomposition products as chloride-adducts by online electrospray ionization mass spectrometry. Experiments involving D 2 O and H 2 18 O instead of H 2 16 O, and an OH-radical scavenger show that -HHs decompose into gem-diols + H 2 O 2 rather than free radicals. -HHs decay mono-or bi-exponentially depending on molecular structure and solvent composition. e-fold times, 1/e , in water-rich solvent mixtures range from 1/e = 15-45 min for monoterpene-derived -HHs to 1/e > 10 3 min for the -Tp