Photooxidation-Initiated Aqueous-Phase Formation of Organic Peroxides: Delving into Formation Mechanisms.

Formation of highly oxygenated molecules (HOMs) such as organic peroxides (ROOR, ROOH, and H2O2) is known to degrade food and organic matter. Gas-phase unimolecular autoxidation and bimolecular RO2 + HO2/RO2 reactions are prominently renowned mechanisms associated with the formation of peroxides. However, the reaction pathways and conditions favoring the generation of peroxides in the aqueous phase need to be evaluated. Here, we identified bulk aqueous-phase ROOHs in varying organic precursors, including a laboratory model compound and monoterpene oxidation products. Our results show that formation of ROOHs is suppressed at enhanced oxidant concentrations but exhibits complex trends at elevated precursor concentrations. Furthermore, we observed an exponential increase in the yield of ROOHs when UV light with longer wavelengths was used in the experiment, comparing UVA, UVB, and UVC. Water-soluble organic compounds represent a significant fraction of ambient cloud-water components (up to 500 µM). Thus, the reaction pathways facilitating the formation of HOMs (i.e., ROOHs) during the aqueous-phase oxidation of water-soluble species add to the climate and health burden of atmospheric particulate matter.

Potential Matrix Effects in Iodometry Determination of Peroxides Induced by Olefins.

Peroxides (H2O2, ROOR, and ROOH) are an important reaction intermediate involved in a number of natural processes, including atmospheric autoxidation and lipid peroxidation in oils and animal tissues. Iodometry is an established spectroscopic technique that has been widely used to quantify total peroxide concentration in food, indoor, and outdoor samples. Iodometry provides selectivity toward peroxides through a quantitative reaction between I- and peroxides to form I3- via a molecular iodine (I2) intermediate. However, equilibrium changes caused by a potential interaction between olefinic species and I2 can suppress I3- formation, thereby underestimating peroxide concentration. For the first time in the current study, this unrecognized interference posed by olefins (OEs) is systematically investigated to gauge its effects on the accuracy of iodometry. A number of model molecules were investigated. The interference was observed to be unique to OEs, but universally affecting different peroxide species such as H2O2, tert-butyl hydroperoxide, and aerosol-bound peroxides. A simple kinetic box model was built to explain this chemistry. The measured rate constant for 3-octenoic acid was found to be 0.84 ± 0.02 M-1 s-1. Overall, our results show matrix effects induced by OEs can underestimate peroxide concentration determined by iodometry for edible oils, indoor environments, and animal fat, but absent in most of the atmospheric samples. Nonetheless, our results point out the importance of this interfering chemistry in matrices enriched with OEs.

Particulate matter emitted from ultrasonic humidifiers-Chemical composition and implication to indoor air.

Household humidification is widely practiced to combat dry indoor air. While the benefits of household humidification are widely perceived, its implications to the indoor air have not been critically appraised. In particular, ultrasonic humidifiers are known to generate fine particulate matter (PM). In this study, we first conducted laboratory experiments to investigate the size, quantity, and chemical composition of PM generated by an ultrasonic humidifier. The mass of PM generated showed a correlation with the total alkalinity of charge water, suggesting that CaCO3 is likely making a major contribution to PM. Ion chromatography analysis revealed a large amount of SO42- in PM, representing a previously unrecognized indoor source. Preliminary results of organic compounds being present in humidifier PM are also presented. A whole-house experiment was further conducted at an actual residential house, with five low-cost sensors (AirBeam) monitoring PM in real time. Operation of a single ultrasonic humidifier resulted in PM2.5 concentrations up to hundreds of µg m-3 , and its influence extended across the entire household. The transport and loss of PM2.5 depended on the rate of air circulation and ventilation. This study emphasizes the need to further investigate the impact of humidifier operation, both on human health and on the indoor atmospheric chemistry, for example, partitioning of acidic and basic compounds.

Autoxidation of glycols used in inhalable daily products: implications for the use of artificial fogs and e-cigarettes.

The use of glycols is seen in various industries and occupations. In the past few decades, the health implications of inhalable glycols have gained public attention. Inhalable glycols may cause adverse health effects, especially for workers in occupations receiving frequent exposure and consumers of glycol-based daily products. Our previous work highlighted the rapid accumulation of formaldehyde and glycolaldehyde in fog juice, thus proposing the occurrence of glycol autoxidation. However, the fundamentals of glycol autoxidation remained unclear and unexplored. Our goal is to investigate the autoxidation of common glycols during indoor storage. Carbonyls were quantified using liquid chromatography-mass spectrometry (LC-MS), and peroxides from autoxidation were monitored via iodometry and UV-Vis spectrometry. The impact of certain factors such as the water mixing ratio and antioxidants (vitamin C) was also investigated. Formation of aldehydes in many glycols was weekly monitored, such as e-cigarette juice and triethylene glycol (TEG). Occurrence of autoxidation was confirmed by the increase in the total peroxide concentration. Additionally, we highlighted the dependence of the carbonyl formation rate on the TEG-water mixing ratio, demonstrating the complex role of water in glycol autoxidation. We have also tested the effectiveness of vitamin C and made suggestions for minimizing the formation of toxic carbonyls in consumer products.