Heterogeneous/multiphase reactions can influence the formation, composition, and chemical–physical properties of secondary organic aerosol (SOA), but data describing their kinetics and equilibria remain sparse. Here, we synthesized and utilized a probe molecule to investigate the condensed phase reactions of hydroperoxides with ketones and aldehydes, including those in SOA generated from the ozonolysis of α-pinene in an environmental chamber. The probe molecule, which contained a hydroperoxide group and a UV-absorbing nitrate group, was mixed with a ketone (3-decanone) or aldehyde (nonanal) and monitored over 24 h using liquid chromatography with UV–vis detection to determine the rate and equilibrium constants for each reaction. The probe molecule did not react with the ketone but reacted reversibly with the aldehyde to form a peroxyhemiacetal, a process that was also catalyzed by carboxylic acid. The rate constant for the reversible decomposition of the peroxyhemiacetal was also measured using attenuated total reflectance Fourier transform infrared spectroscopy. The forward (f) and reverse (r) rate constants for uncatalyzed (u) and catalyzed (c) peroxyhemiacetal formation were k f,u = 1.5 ± 0.4 M–1 h–1, k r,u = 0.16 ± 0.001 h–1, k f,c = 0.62 ± 0.07 M–2 h–1, and k r,c = 0.055 ± 0.006 M–1 h–1; and the equilibrium constant was K eq = 9.1 ± 2 M–1. No evidence of Baeyer–Villiger decomposition of the peroxyhemiacetal was observed. When mixed with α-pinene/O3 SOA, the probe molecule reached reaction equilibrium within 20 min, indicating that atmospheric timescales for peroxyhemiacetal formation can be short. Using the results of the nonanal experiments and measured carbonyl content of the SOA, we estimate that up to 25% of the carbonyls in this SOA was aldehydes.

Environmental chamber studies are widely used for measuring the yields of reaction products and secondary organic aerosol formed from the oxidation of volatile organic compounds, information that can be subsequently used to develop chemical reaction mechanisms and models of atmospheric chemistry. Such measurements are challenging, however, and many potential sources of errors are not always appreciated. Here, we describe methods for minimizing and accounting for uncertainties associated with the chamber volume, gas and particle sampling, instrument calibrations, gas–wall partitioning, particle deposition to walls, and secondary reactions with OH radicals and demonstrate these methods by measuring yields and branching ratios for the formation of β-hydroxynitrates from reactions of C14 and C15 1-alkenes with OH radicals in the presence of NO x . Experiments were conducted in a Teflon environmental chamber and included Tenax sampling of alkenes with analysis by gas chromatography with flame ionization detection, filter sampling of particle-phase β-hydroxynitrates and dioctyl phthalate seed particles with analysis by liquid chromatography with UV/vis detection, and measurements of aerosol volume concentration and composition using a scanning mobility particle sizer and thermal desorption particle beam mass spectrometer. The measured yields of β-hydroxynitrates are ∼25% higher than those determined previously using similar methods whose uncertainties were less well minimized and characterized.

The reactions of 1-tetradecene and 1-pentadecene, the C14 and C15 linear 1-alkenes, with OH radicals in the presence of NO x were investigated in a series of environmental chamber experiments. Particle-phase β-hydroxynitrates, dihydroxynitrates, dihydroxycarbonyls, and 1,4-hydroxynitrates and gas-phase aldehydes were sampled and then identified and quantified using a suite of offline analytical techniques that included derivatization, gas and liquid chromatography, and multiple types of mass spectrometry. Measured molar yields of products formed by OH radical addition to the CC double bond, including β-hydroxynitrates, dihydroxynitrates, dihydroxycarbonyls (which have not been previously directly quantified with high accuracy), and aldehydes were 0.125 ± 0.01, 0.048 ± 0.005, 0.240 ± 0.04, and 0.268 ± 0.03 (0.264 ± 0.02 and 0.271 ± 0.04 for the formaldehyde and tridecanal/tetradecanal co-products of β-hydroxyalkoxy radical decomposition), respectively. These values give a total molar yield of 0.681 ± 0.05, which agrees very well with the results of kinetics measurements that indicate that the fraction of reaction that occurs by OH radical addition is 0.70. The yields were used to calculate branching ratios for all OH radical addition pathways, including a value of 0.18 for the formation of dihydroxynitrates from the reaction of dihydroxyperoxy radicals with NO and values of 0.47 and 0.53 for β-hydroxyalkoxy radical decomposition and isomerization. The results were used with literature data on the yields of aldehydes measured for similar reactions of smaller alkenes, a model for the effect of carbon number on branching ratios for organic nitrate formation, and a mechanism for H atom abstraction derived from studies of linear alkanes to achieve a complete, quantitative gas-phase reaction mechanism for 1-alkenes. The results should also be useful for constructing mechanisms for more complex reactions of volatile organic compounds.