Measurements of Kinetics and Equilibria for the Condensed Phase Reactions of Hydroperoxides with Carbonyls to Form Peroxyhemiacetals

Abstract

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.

Dynamic Oxidative Potential of Organic Aerosol from Heated Cooking Oil

“…This chain reaction is terminated by reactions such as RO 2 + HO 2 and RO 2 + RO 2 , resulting in the formation of multifunctional peroxides . Another possible pathway for these alkenals to form peroxides is via OH-initiated H abstraction on the aldehyde group, which forms the peroxy acid. , Interactions between carbonyls and peroxides can further produce peroxyhemiacetals/ketals with lower volatilities, which may increase the gas-to-particle partitioning of organic peroxides . In summary, the significant peroxide content observed in SOA from heated cooking oil could be explained by the photooxidation of alkenals in our study.…”

Estimation of secondary organic aerosol viscosity from explicit modeling of gas-phase oxidation of isoprene and <i>α</i>-pinene

“…It has been observed that ambient SOA particles can bounce off from an impactor stage depending on ambient conditions, indicating non-liquid states of organic particles (Virtanen et al, 2011;Bateman et al, 2017;Slade et al, 2019). Measurements of the viscosity of SOA bulk materials derived from the oxidation of limonene (Hinks et al, 2016), toluene (Song et al, 2016), α-pinene (Renbaum-Wolff et al, 2013;Kidd et al, 2014;Bateman et al, 2015;Zhang et al, 2015;Grayson et al, 2016;Hosny et al, 2016) and isoprene (Song et al, 2015) have confirmed that viscosity of SOA particles can vary depending on temperature and RH . In addition, previous studies have shown that SOA chemical composition can be affected by experimental conditions upon SOA formation such as RH and particle mass concentrations (Kidd et al, 2014;Hinks et al, 2018;Grayson et al, 2016;Jain et al, 2018).…”

“…Figure 5. Simulated functional group distributions in particle-phase compounds derived from isoprene photooxidation (Song et al, 2015) and α-pinene ozonolysis (Bateman et al, 2015;Kidd et al, 2014;Grayson et al, 2016;Zhang et al, 2015;Renbaum-Wolff et al, 2013). sons for the discrepancies between measurements and simulations of SOA viscosity.…”

Reply on RC2

“…Chemical composition simulated for Zhang's experiments is characterized by the highest -RCHO fraction among all experiments, which may explain the largest difference between predicted and measured viscosities. Aldehydes are known to be highly reactive in the condensed phase by reacting with alcohols and hydroperoxides to form peroxyhemiacetals and oligomers (Ziemann and Atkinson, 2012) Such multiphase reactions could be accelerated under acidic conditions in the presence of carboxylic acids (Bakker-Arkema and Ziemann, 2020;Shiraiwa et al, 2013 Bateman et al, 2015Kidd et al, 2014Grayson et al, 2016Zhang et al, 2015Renbaum-Wolff et al, 2013 Figure 5. Simulated functional group distributions in particle-phase compounds derived from α-pinene ozonolysis for various experiments.…”