Ozonolysis Products Research Articles

Structurally Selective Ozonolysis of p-Phenylenediamines and Toxicity in Coho Salmon and Rainbow Trout.

The tire-rubber-derived ozonation product of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-Q), was recently discovered to cause acute mortality in coho salmon (Oncorhynchus kisutch). para-Phenylenediamines (PPDs) with variable side chains distinct from 6PPD have been identified as potential replacement antioxidants, but their toxicities remain unclear under environmentally relevant ozone conditions. We herein tested the multiphase gas-surface ozone reactivity of four select PPDs [6PPD, N-isopropyl-N'-phenyl-p-phenylenediamine (IPPD), N,N'-diphenyl-p-phenylenediamine (DPPD), and N-phenyl-N'-cyclohexyl-p-phenylenediamine (CPPD)] and evaluated the toxicity of their reaction mixtures in coho salmon, rainbow trout (Oncorhynchus mykiss), and fathead minnow (Pimephales promelas). 6PPD and IPPD were found to rapidly react with ozone, while no significant multiphase ozone reactivity was observed for DPPD or CPPD. The viability of coho salmon CSE-119 cells was strongly affected by the ozonolysis products of 6PPD but not by those of the other three PPDs. Acute mortality was only observed in juvenile rainbow trout that were exposed to oxidized 6PPD, suggesting a common mechanism of toxic action in the two salmonid fish species. This study reports the structurally selective ozone reactivity of PPDs and the unique toxicity of 6PPD ozonolysis mixtures, which demonstrates that other PPDs are potential alternative antioxidants.

Investigation of the Cyclohexene Oxidation Mechanism Through the Direct Measurement of Organic Peroxy Radicals.

Monoterpenes, the second most abundant biogenic volatile organic compounds globally, are crucial in forming secondary organic aerosols, making their oxidation mechanisms vital for addressing climate change and air pollution. This study utilized cyclohexene as a surrogate to explore first-generation products from its ozonolysis through laboratory experiments and mechanistic modeling. We employed proton transfer reaction mass spectrometry with NH4+ ion sources (NH4+-CIMS) and a custom-built OH calibration source to quantify organic peroxy radicals (RO2) and closed-shell species. Under near-real atmospheric conditions in a Potential Aerosol Mass-Oxidation Flow Reactor, we identified 30 ozonolysis products, expanding previous data sets of low-oxygen compounds. Combined with simulations based on the Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere and relevant literature, our results revealed that OH dominates over ozone in cyclohexene oxidation at typical atmospheric oxidant levels with H-abstraction contributing 30% of initial RO2 radicals. Highly oxidized molecules primarily arise from RO2 autoxidation initiated by ozone, and at least 15% of ozone oxidation products follow the overlooked nonvinyl hydroperoxides pathway. Gaps remain especially in understanding RO2 cross-reactions, and the structural complexity of monoterpenes further complicates research. As emissions decrease and afforestation increases, understanding these mechanisms becomes increasingly critical.

Modeling impacts of indoor environmental variables on secondary organic aerosol formation

There are numerous air pollutants indoors including chemicals emitted from building environments as well as outdoor-origin species due to human activities. Despite the significance of indoor air quality, the atmospheric process indoors is not well studied. In this study, the secondary organic aerosol (SOA) formation from the oxidation of α-pinene blended with toluene was simulated under varying indoor environments (lamps, NO2, ozone, and inorganic seed) using the UNIfied Partitioning Aerosol Reaction (UNIPAR) model. Explicitly predicted lumping species produced during the atmospheric oxidation of precursors are used in the model and they process multiphase partitioning and aerosol phase reactions. The performance of the model was demonstrated using indoor chamber experiments in both dark conditions (ozonolysis) and light conditions with commercialized fluorescent or LED lamps. α-Pinene SOA was dominated by ozonolysis even in the presence of indoor light. Toluene, which is known to be photochemically processed, was oxidized in the dark condition with OH radicals that were derived from ozonolysis products of α-pinene. At given dark simulation conditions (10 ppb α-pinene, 30 ppb ozone, and 50 ppb of toluene), toluene contributed 15 % of SOA mass. α-Pinene SOA was insensitive to hygroscopicity of inorganic seed, but toluene blended with α-pinene increased the sensitivity to seed conditions due to the formation of oligomeric matter via aqueous reactions of reactive toluene products. In the presence of NO2. α-pinene SOA formation significantly increased with increasing NO2 owing to the reaction of α-pinene with nitrate radicals to form low volatile products. This study concludes that ozone and NO2, intruded from outdoors to indoors, effectively oxidize terpenes and furthermore aromatic hydrocarbons with OH radicals originating from ozonolysis of terpenes. The reaction paths with ozone and nitrate radicals are more effective at forming SOA than that with OH radical under the indoor light condition with commercialized lamps.

Oxidation of metazachlor herbicide by ozone in the gas and aqueous phases: mechanistic, kinetics, and ecotoxicity studies.

The atmospheric and aqueous ozonolysis of metazachlor (MTZ) is investigated using high-level quantum chemical and kinetic calculations (M06-2X/6-311 + + G(3df,3pd)//M06-2X/6-31 + G(d,p) level of theory). The ozone (O3)-initiated degradation pathways of MTZ under three different mechanisms, namely cycloaddition, oxygen-addition, and single electron transfer (SET), are explored in the temperature range of 283-333K and 1atm pressure. As a result, the cycloaddition reaction at the C16C18 double bond of the benzene ring of MTZ is found to be the most dominant channel in the atmosphere with thestandardGibbs free energy of reaction (ΔrG0g) of - 129.13kJmol-1 and the highest branching ratio of 95.18%. In the aqueous phase, the main reaction channel turns into the SET mechanism, which owns the lowest Gibbs free energy of activation (ΔG#aq) of 73.8kJmol-1 and contributes 87.8% to the ktotal. Over the temperature range of 283-333K, the total rate constant (ktotal) significantly increases from 8.42 to 5.82 × 101M-1s-1 in the atmosphere and from 4.10 × 102 to 2.40 × 104M-1s-1 in the aqueous environment. Remarkably, the ecotoxicity assessment shows that MTZ may be harmful to fish and chronically harmful to daphnia. In contrast, its main ozonolysis products exhibit no acute or chronic toxicity or mutagenic effects.

Ultrafine particles formation from ozonolysis of gas- and particle-phases of cigarette smoke

Cigarette smoke and ozone (O3) are two main pollutants in indoor environments and their mutual reaction can generate substantial detrimental substances having synergistic influences on the environment and human health. The aging process of cigarette smoke in the atmosphere is mainly gone through ozonolysis reaction attracting increasing attention in recent years. Herein, the ozonolysis reaction of cigarette smoke with indoor O3 concentrations has been investigated in a Teflon chamber. The gas- and particle-phases of cigarette smoke are divided and their individual ozonolysis process can generate ultrafine particles (UFPs) with high number concentrations. The chemical compositions of the gas- and particle-phases of cigarette smoke as well as their nascent UFPs are measured and their differences during the ozonolysis have been clearly observed with vacuum ultraviolet (VUV) photoionization mass spectrometry. In particular, several representative key species of cigarette smoke, i.e., the gas-phase furan and 2,5-dimethylfuran and the particle-phase nicotine, as well as their ozonolysis products are definitely identified and play an important role in the nucleation formation of UFPs. Their ozonolysis reaction mechanisms are also discussed. In addition, this work demonstrates that the ozonolysis of the particle-phase of cigarette smoke contributes more UFPs than that of the gas-phase.

How Does Personal Hygiene Influence Indoor Air Quality?

Humans are known to be a continuous and potent indoor source of volatile organic compounds (VOCs). However, little is known about how personal hygiene, in terms of showering frequency, can influence these emissions and their impact on indoor air chemistry involving ozone. In this study, we characterized the VOC composition of the air in a controlled climate chamber (22.5 m3 with an air change rate at 3.2 h-1) occupied by four male volunteers on successive days under ozone-free (∼0 ppb) and ozone-present (37-40 ppb) conditions. The volunteers either showered the evening prior to the experiments or skipped showering for 24 and 48 h. Reduced shower frequency increased human emissions of gas-phase carboxylic acids, possibly originating from skin bacteria. With ozone present, increasing the number of no-shower days enhanced ozone-skin surface reactions, yielding higher levels of oxidation products. Wearing the same clothing over several days reduced the level of compounds generated from clothing-ozone reactions. When skin lotion was applied, the yield of the skin ozonolysis products decreased, while other compounds increased due to ozone reactions with lotion ingredients. These findings help determine the degree to which personal hygiene choices affect the indoor air composition and indoor air exposures.

Synthesis of polyfunctional O-containing 1,3-dioxepines connected with an acetal fragment by low-temperature ozonolysis

The synthesis of 3,5-dioxo-1,7-heptandials, 3,5-dioxo-1,7-heptanediols and 1,3-dioxo-1,7-heptanedicarboxylic acid derivatives by low-temperature ozonolysis of 1,3-dioxepines was carried out for the first time. It is shown that, depending on the conditions of destruction of the intermediate peroxide products of ozonolysis, the corresponding individual dialdehydes, diols, and diesters can be synthesized with high selectivity.

Ozonolysis of 2-Methyl-2-pentenal: New Insights from Master Equation Modeling.

Experimental and theoretical studies were carried out to investigate the ozonolysis of trans-2-methyl-2-pentenal. The experiments were conducted in atmospheric simulation chambers coupled to a Fourier transform infrared (FTIR) spectrometer and a gas chromatograph-mass spectrometer at room temperature and atmospheric pressure in the presence of an excess of cyclohexane in dry conditions (RH < 1%). The ozonolysis reaction was investigated theoretically from the results of accurate density functional (M06-2X) and ab initio [CCSD(T)] computations, employing the AVTZ basis set. The sequence of reaction steps was established, and the system of kinetics equations was modeled using MESMER. In the first step, a primary ozonide is formed, which then decomposes along two pathways. The principal ozonolysis products are propanal, methylglyoxal, ethylformate, and a secondary ozonide. An interesting competition between sequential reaction steps and well-skipping is found, which leads to an inversion of the expected methylglyoxal/propanal product ratio at temperatures below 210 K. The mechanism of the "hot ester" reaction channel of the Criegee intermediate was revisited. The computed ozonolysis rate constant and product branching ratio are in excellent agreement with the experimental data that are also reported in the present work.

Functional Group Analysis of α-Pinene Oxidation Products Using Derivatization Reactions and High-Resolution Electrospray Ionization Collision-Induced Dissociation Mass Spectrometry.

Oxidation products of monoterpenes (C10H16) play a significant role as precursors for secondary organic aerosol formation. They contain several structural isomers with multifunctional groups. However, only a few of these isomers have been identified experimentally. We describe a measurement technique for identifying oxygen-containing functional groups (carbonyl, carboxyl, and hydroxyl groups) included in monoterpene oxidation products. This technique involves (i) three derivatization reactions (oximation of carbonyls by O-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine, methyl esterification of carboxylic acids by trimethylsilyl diazomethane, and acylation of alcohols by acetic anhydride), (ii) no preseparation high-resolution electrospray ionization mass spectrometry, and (iii) collision-induced dissociation. This technique was applied to functional group analysis of ozonolysis products for α-pinene. Multifunctional groups of known ozonolysis products were accurately identified. Furthermore, we successfully estimated the multifunctional groups of products that have not been previously reported.

Gas-to-Particle Partitioning of Products from Ozonolysis of Δ3-Carene and the Effect of Temperature and Relative Humidity.

Formation of oxidized products from Δ3-carene (C10H16) ozonolysis and their gas-to-particle partitioning at three temperatures (0, 10, and 20 °C) under dry conditions (<2% RH) and also at 10 °C under humid (78% RH) conditions were studied using a time-of-flight chemical ionization mass spectrometer (ToF-CIMS) combined with a filter inlet for gases and aerosols (FIGAERO). The Δ3-carene ozonolysis products detected by the FIGAERO-ToF-CIMS were dominated by semivolatile organic compounds (SVOCs). The main effect of increasing temperature or RH on the product distribution was an increase in fragmentation of monomer compounds (from C10 to C7 compounds), potentially via alkoxy scission losing a C3 group. The equilibrium partitioning coefficient estimated according to equilibrium partitioning theory shows that the measured SVOC products distribute more into the SOA phase as the temperature decreases from 20 to 10 and 0 °C and for most products as the RH increases from <2 to 78%. The temperature dependency of the saturation vapor pressure (above an assumed liquid state), derived from the partitioning method, also allows for a direct way to obtain enthalpy of vaporization for the detected species without accessibility of authentic standards of the pure substances. This method can provide physical properties, beneficial for, e.g., atmospheric modeling, of complex multifunctional oxidation products.

Impacts of α-pinene ozonolysis products on the morphology and optical properties of black carbon

Black carbon (BC) is known to absorb solar radiation and thus have a warming impact on climate. The atmospheric aging of fresh BC has been suggested to enhance BC's light absorption, but the extent of variation observed varies largely in field and laboratory measurements. Biogenic VOCs with much higher abundance than anthropogenic emissions are reactive towards atmospheric oxidants, and act as major sources of secondary organic aerosol (SOA) in the atmosphere. In this study, we performed experiments of BC aging in the presence of condensable organic vapors generated from the ozonolysis of α-pinene. Significant changes in the particle size, mass, effective density, morphology as well as optical properties are observed upon coating of BC by α-pinene ozonolysis products. While the BC aging rate depends on the initial concentrations of precursors forming condensable materials and the particle size, the extent of transformation of BC at a given size is mainly controlled by the volume equivalent coating thickness. The highly fractal BC core is converted to a more compact morphology for a coating thickness of ∼25–30 nm depending on the initial particle size. The absorption and scattering of light by BC also increase by more than 1.29- and 5.30- fold during the coating process. The enhancement of optical properties can be attributed to both formation of coatings and restructuring of the BC core, with the latter accounting for a large fraction of optical enhancement. Our results indicate that the ozonolysis of α-pinene has profound effects on the morphology and optical properties of BC, with a magnitude comparable to sulfuric acid and ammonium nitrate, but much higher than other reported anthropogenic hydrocarbons. Although present in relatively low concentrations, α-pinene oxidation reactions can considerably enhance the impacts of BC on air quality and climate forcing.

A Novel Approach for Glycero-(9,10-trioxolane)-Trialeate Incorporation into Poly(lactic acid)/Poly(ɛ-caprolactone) Blends for Biomedicine and Packaging.

The product of ozonolysis, glycero-(9,10-trioxolane)-trioleate (ozonide of oleic acid triglyceride, [OTOA]), was incorporated into polylactic acid/polycaprolactone (PLA/PCL) blend films in the amount of 1, 5, 10, 20, 30 and 40% w/w. The morphological, mechanical, thermal and antibacterial properties of the biodegradable PLA/PCL films after the OTOA addition were studied. According to DSC and XRD data, the degree of crystallinity of the PLA/PCL + OTOA films showed a general decreasing trend with an increase in OTOA content. Thus, a significant decrease from 34.0% for the reference PLA/PCL film to 15.7% for the PLA/PCL + 40% OTOA film was established using DSC. Observed results could be explained by the plasticizing effect of OTOA. On the other hand, the PLA/PCL film with 20% OTOA does not follow this trend, showing an increase in crystallinity both via DSC (20.3%) and XRD (34.6%). OTOA molecules, acting as a plasticizer, reduce the entropic barrier for nuclei formation, leading to large number of PLA spherulites in the plasticized PLA/PCL matrix. In addition, OTOA molecules could decrease the local melt viscosity at the vicinity of the growing lamellae, leading to faster crystal growth. Morphological analysis showed that the structure of the films with an OTOA concentration above 20% drastically changed. Specifically, an interface between the PLA/PCL matrix and OTOA was formed, thereby forming a capsule with the embedded antibacterial agent. The moisture permeability of the resulting PLA/PCL + OTOA films decreased due to the formation of uniformly distributed hydrophobic amorphous zones that prevented water penetration. This architecture affects the tensile characteristics of the films: strength decreases to 5.6 MPa, elastic modulus E by 40%. The behavior of film elasticity is associated with the redistribution of amorphous regions in the matrix. Additionally, PLA/PCL + OTOA films with 20, 30 and 40% of OTOA showed good antibacterial properties on Pseudomonas aeruginosa, Raoultella terrigena (Klebsiella terrigena) and Agrobacterium tumefaciens, making the developed films potentially promising materials for wound-dressing applications.

Investigation of RH effect on uncommon limonene ozonolysis products and SOA formation in indoor air with real time measurement techniques

Scientific interest in SOA influence on indoor air quality increases since last 20 years. It is well known, that particles of nano-sized diameter pose a threat for human health causing, among others: eye, upper airway irritation, inflammatory response in cells, worsening asthma, hypertension, diabetes, and central nervous dysfunction. Terpenes are reactive VOCs, commonly emitted in indoor air and considered to be SOA precursors by oxidation reactions. The aim of this study was to investigate the relative humidity influence on i) formation of limonene ozonolysis products and ii) SOA formation process – especially the first steps of it. We managed to determine 4 uncommon limonene ozonolysis products (m/z: 43, 83, 99 and 110) appearing in the PTR-TOF-MS mass spectra with the same frequency as well-known formaldehyde, acetone, acetic acid and formic acid. We also detected m/z 75 and m/z 115 formed under dry conditions and m/z 111 and m/z 125 formed under humid conditions. Detected masses formula is proposed with probability >70 % and the probability is derived from the deviation of the exact mass to the measured one and the isotope distribution. SMPS data analysis allowed us to conclude that RH around 40% increases particle mass concentration, regardless initial limonene concentration. Unfortunately, conclusions about RH influence on particle number concentration are inconsistent. Under low initial terpene concentration, RH around 40% decreases particle number concentration. However, for high initial limonene concentration, RH around 40% caused increase in particle number concentration. Obtained results allowed to conclude, that i) RH influences both particle number and particle mass concentration, ii) initial substrate concentration influences SOA formation altering the RH effect, iii) comparison of results and drawing conclusions is difficult due to different experimental protocols in the literature and due to the number of factors influencing SOA formation initiated by terpene oxidation.

Chemical Fate of Oils on Indoor Surfaces: Ozonolysis and Peroxidation.

Unsaturated triglycerides found in food and skin oils are reactive in ambient air. However, the chemical fate of such compounds has not been well characterized in genuine indoor environments. Here, we monitored the aging of oil coatings on glass surfaces over a range of environmental conditions, using mass spectrometry, nuclear magnetic resonance (NMR), and electron paramagnetic resonance (EPR) techniques. Upon room air exposure (up to 17 ppb ozone), the characteristic ozonolysis products, secondary ozonides, were observed on surfaces near the cooking area of a commercial kitchen, along with condensed-phase aldehydes. In an office setting, ozonolysis is also the dominant degradation pathway for oil films exposed to air. However, for indoor enclosed spaces such as drawers, the depleted air flow makes lipid autoxidation more favorable after an induction period of a few days. Forming hydroperoxides as the major primary products, this radical-mediated peroxidation behavior is accelerated by indoor direct sunlight, but the initiation step in dark settings is still unclear. These results are in accord with radical measurements, indicating that indoor photooxidation facilitates radical formation on surfaces. Overall, many intermediate and end products observed are reactive oxygen species (ROS) that may induce oxidative stress in human bodies. Given that these species can be widely found on both food and household surfaces, their toxicological properties are worth further attention.

MALDI-MS screening of microbial colonies with isomer resolution to select fatty acid desaturase variants

Creating controlled lipid unsaturation locations in oleochemicals can be a key to many bioengineered products. However, evaluating the effects of modifications to the acyl-ACP desaturase on lipid unsaturation is not currently amenable to high-throughput assays, limiting the scale of redesign efforts to <200 variants. Here, we report a rapid MS assay for profiling the positions of double bonds on membrane lipids produced by Escherichia coli colonies after treatment with ozone gas. By MS measurement of the ozonolysis products of Δ6 and Δ8 isomers of membrane lipids from colonies expressing recombinant Thunbergia alata desaturase, we screened a randomly mutagenized library of the desaturase gene at 5 s per sample. Two variants with altered regiospecificity were isolated, indicated by an increase in 16:1 Δ8 proportion. We also demonstrated the ability of these desaturase variants to influence the membrane composition and fatty acid distribution of E. coli strains deficient in the native acyl-ACP desaturase gene, fabA. Finally, we used the fabA deficient chassis to concomitantly express a non-native acyl-ACP desaturase and a medium-chain thioesterase from Umbellularia californica, demonstrating production of only saturated free fatty acids.

A combined gas- and particle-phase analysis of highly oxygenated organic molecules (HOMs) from α-pinene ozonolysis

Abstract. Highly oxygenated organic molecules (HOMs) are important for the formation of secondary organic aerosol (SOA), which poses serious health risks and exerts great influence on Earth's climate. However, the speciation of particle-phase HOMs and its relationship with gas-phase HOM formation has been limited by the lack of suitable analytical techniques. Here, combining a novel particle evaporation inlet, the VIA (Vaporization Inlet for Aerosols), with a nitrate chemical ionization mass spectrometer (NO3-CIMS), gas- and particle-phase HOM products of α-pinene ozonolysis were studied under different conditions. Within the 50 min residence time of our Teflon chamber, we observed enhancement of C16–C19 HOM dimers in particles compared to the HOMs that were condensing. In particular, gas-phase dimer formation was considerably suppressed in experiments with the addition of CO or NO, but dimers still made up a considerable fraction of the observed SOA. In addition to the generally shorter carbon skeletons of the particle-phase dimers (i.e., C16–C19) compared to the gas phase (C19–C20), average O/C ratios of the HOMs (especially in the dimer range) also decreased slightly in the particle phase. C17H26Oz compounds, which have often been reported by previous offline measurements, dominate the particle-phase HOM mass spectra in α-pinene ozonolysis experiments. Our results indicate that these C17 compounds might be related to particle-phase processes within 1 h after HOM condensation. However, the new VIA–NO3-CIMS system used in this work will require more detailed characterization to better understand how the thermal desorption and wall effects may modify the measured particle-phase HOM distributions. Nevertheless, organic nitrate, for example, measured by this novel VIA–NO3-CIMS system was consistent with the measurements of an Aerodyne aerosol mass spectrometer (AMS), showing the capability of this system as a promising technique for particle-phase HOM measurements. Taken together, we believe that this system is a promising technique for combined online gas- and particle-phase HOM measurements.

Predicting the environmental fates of emerging contaminants: Synergistic effects in ozone reactions of nitrogen-containing alkenes.

While nitro and amino alkenes are common in pharmaceuticals, pesticides, and munitions, their environmental fates are not well known. Ozone is a ubiquitous atmospheric oxidant for alkenes, but the synergistic effects of nitrogen-containing groups on the reactions have not been measured. The kinetics and products of ozonolysis of a series of model compounds with different combinations of these functional groups have been measured in the condensed phase using stopped-flow and mass spectrometry methods. Rate constants span about six orders of magnitude with activation energies ranging from 4.3 to 28.2 kJ mol-1. Vinyl nitro groups substantially decrease the reactivity, while amino groups have the opposite effect. The site of the initial ozone attack is highly structure dependent, consistent with local ionization energy calculations. The reaction of the neonicotinoid pesticide nitenpyram, which forms toxic N-nitroso compounds, was consistent with model compounds, confirming the utility of model compounds for assessing environmental fates of these emerging contaminants.

Atmospheric fate of typical liquid crystal monomers in the tropospheric gas, liquid, and granular phases

Mineral aerosol particles significantly impact environmental risk prediction of liquid crystal monomers (LCMs). In this work, we investigated the reaction mechanisms and kinetics of three typical LCMs (4-cyano-3,5-difluorophenyl 4-ethylbenzoate (CEB-2F), 4-cyano-3-fluorophenyl 4-ethylbenzoate (CEB-F), and 4-cyanophenyl 4-ethylbenzoate (CEB)) with ozone (O3) in the atmospheric gas, liquid, and particle phases employing density functional theory (DFT). Here, O3 is prone to add to the benzene ring without F atom(s) in the selected LCMs. The ozonolysis products are aldehydes, carboxylic acids, epoxides, and unsaturated hydrocarbons containing aromatic rings. Those products undergo secondary ozonolysis to generate small molecular compounds such as glyoxal, which is beneficial for generating secondary organic aerosol (SOA). Titanium dioxide (TiO2), an essential component of mineral aerosol particles, has good adsorption properties for LCMs; however, it slightly reduces the reactivity with O3. At 298 K, the reaction rate constant of the selected LCMs reacting with O3 in the gas and atmospheric liquid phases is (2.74‒5.53) × 10−24 cm3/(mol·sec) and 5.58 × 10−3‒39.1 L/(mol·sec), while CEB-2F reacting with O3 on (TiO2)6 cluster is 1.84 × 10−24 cm3/(mol·sec). The existence of TiO2 clusters increases the persistence and long-distance transportability of LCMs, which enlarges the contaminated area of LCMs.

Adsorption of 6-MHO on two indoor relevant surface materials: SiO2 and TiO2.

The compound 6-methyl-5-hepten-2-one (6-MHO) is a product of skin oil ozonolysis and is of significance in understanding the role of human occupants in the indoor environment. We present a joint computational and experimental study investigating the adsorption of 6-MHO on two model indoor relevant surfaces, SiO2, a model for a glass window, and TiO2, a component of paint and self-cleaning surfaces. Our classical force field-based molecular dynamics, ab initio molecular dynamics simulations, and FTIR absorption spectra indicate 6-MHO can adsorb on to both of these surfaces via hydrogen and π-hydrogen bonds and is quite stable due to the linear geometry of 6-MHO. Detailed analysis of 6-MHO on the SiO2 surface shows that relative humidity does not impact surface adsorption and adsorbed water does not displace 6-MHO from the hydroxylated SiO2 surface. Additionally, the desorption kinetics of 6-MHO from the hydroxylated SiO2 surface is compared to other compounds found in indoor environments and 6-MHO is shown to desorb with a first order rate constant that is approximately four times slower than that of limonene, but six times faster than that of carvone. In addition, our joint results indicate 6-MHO forms a stronger interaction with the TiO2 surface compared to the SiO2 surface. This study suggests that skin oil ozonolysis products can partition to indoor surfaces leading to the formation of organic films.

Quantifying the impact of relative humidity on human exposure to gas phase squalene ozonolysis products

Models were developed to treat Criegee chemistry and estimate gas-phase squalene ozonolysis products under different conditions. Relative humidity can significantly impact human exposure to these products.