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

Transient absorption spectra and decay profiles of HO2 have been measured using cw near-IR two-tone frequency modulation absorption spectroscopy at 297 K and 50 Torr in diluent of N2 in the presence of water. From the depletion of the HO2 absorption peak area following the addition of water, the equilibrium constant of the reaction HO2 + H2O <--> HO2-H2O was determined to be K2 = (5.2 +/- 3.2) x 10(-19) cm3 molecule(-1) at 297 K. Substituting K2 into the water dependence of the HO2 decay rate, the rate coefficient of the reaction HO2 + HO2-H2O was estimated to be (1.5 +/- 0.1) x 10(-11) cm3 molecule(-1) s(-1) at 297 K and 50 Torr with N2 as the diluent. This reaction is much faster than the HO2 self-reaction without water. It is suggested that the apparent rate of the HO2 self-reaction is enhanced by the formation of the HO2-H2O complex and its subsequent reaction. Results are discussed with respect to the kinetics and atmospheric chemistry of the HO2-H2O complex. At 297 K and 50% humidity, the concentration ratio of [HO2-H2O]/[HO2] was estimated from the value of K2 to be 0.19 +/- 0.11.

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 matrixes. 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 C15 diolefin in water (W):acetonitrile (AN) mixtures of variable composition containing inert NaCl. α-HH decays into a gem-diol + H2O2 within τ1/e ≈ 52 min in 50% (v:v) water, but persists longer than a day in ≤10% water mixtures. The strong nonlinear dependence of τ1/e on solvent composition reveals that water content is a major factor controlling the fate of α-HHs in atmospheric particles. It also suggests that α-HH decomposes while embedded in WnANm clusters rather than randomly dissolved in molecularly homogeneous W:AN mixtures.

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In the atmosphere, most biogenic terpenes undergo ozonolysis in the presence of water to form reactive α-hydroxyalkyl-hydroperoxides (α-HHs), and the lifetimes of these α-HHs are a key parameter for understanding the processes that occur during the aging of atmospheric particles. We previously reported that α-HHs generated by ozonolysis of terpenes decompose in water to give H 2 O 2 and the corresponding aldehydes, which undergo hydration to form gem-diols. Herein, we report that this decomposition process was dramatically accelerated by acidification of the water with oxalic, acetic, hexanoic, cis-pinonic, or hydrochloric acid. In acidic solution, the temporal profiles of the α-HHs, detected as their chloride adducts by electrospray mass spectrometry, showed single-exponential decays in the pH range from 4.1 to 6.1, and the first-order rate coefficients (k) for the decays increased with decreasing pH. The lifetime of the α-HH derived from α-terpineol was 128 min (k = (1.3 ± 0.4) × 10 −4 s −1 ) at pH 6.1 but only 8 min (k = (2.1 ± 0.1) × 10 −3 s −1 ) at pH 4.1. Because the rate coefficients increased as the pH decreased and the increase depended on pH rather than on the properties of the acid, we propose that the decomposition of the α-HHs in water was specifically catalyzed by H + . Fast H + -catalyzed decomposition of α-HHs could be an important source of H 2 O 2 and multifunctionalized compounds found in ambient atmospheric particles.

In the atmosphere, carbonyl oxides known as Criegee intermediates are produced mainly by ozonolysis of volatile organic compounds containing C=C double bonds, such as biogenic terpenoids. Criegee intermediates can react...

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