Quantifying Ozone-Dependent Emissions of Volatile Organic Compounds from the Human Body

A model of the spatiotemporal distribution of ozone-squalene reaction and ozonolysis by-products from human body

Emissions of ozone and its by-products from ozonolysis on human surfaces lead to indoor air pollution. However, the spatiotemporal distribution of such emissions in indoor environments remains unclear, which may introduce bias when assessing human exposure to ozone and ozonolysis byproducts. This study developed a computational fluid dynamics model to describe the physical and chemical processes involved in the emission of ozone-dependent volatile organic compounds from the human body. The results showed that the reaction probability of ozone in the human body depends on the ozone concentration in the bulk air. For ozone concentrations ranging from 28 ppb to 200 ppb, the reaction probabilities ranged from 5.9 × 10-5 to 1.5 × 10-4. The concentrations of ozone and ozonolysis byproducts obtained from the experimental measurements were used for model validation. The ozonolysis by-products were found to be uniformly distributed in the chamber, whereas the ozone distribution showed less uniformity. The ozone concentration near the human surface was approximately 30 %∼50 % of that in the ambient air. Overall, a model was developed to understand the effect of ozone-surface interactions on indoor air quality. This model can be applied to analyze human exposure to ozone and ozonolysis byproducts and for health risk assessment in built environments.

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.

Proposals for gas-detection improvement of the FeMPc monolayer towards ethylene and formaldehyde by using bimetallic synergy

Development and fabrication of a novel gas sensor with superb performance are crucial for enabling real-time monitoring of ethylene (C2H4) and formaldehyde (H2CO) emissions from industrial manufacture. Herein, first-principles calculations and AIMD simulations were carried out to investigate the effect of the Fe-M dimer on the adsorption of C2H4 and H2CO on metal dimer phthalocyanine (FeMPc, M = Ti-Zn) monolayers, and the electronic structures and sensing properties of the above adsorption systems were systematically discussed. The results show that the FeMPc (M = Ti, V, Cr, Mn) monolayers interact with C2H4 and H2CO by chemisorption except for the FeMnPc/H2CO system, while the other adsorption systems are all characterized by physisorption. Interestingly, the adsorption strength of C2H4 and H2CO can be effectively regulated by the bimetallic synergy of the Fe-M dimer. Moreover, the FeCrPc and FeMnPc monolayers exhibit excellent sensitivity towards C2H4 and H2CO, and have short recovery time (4.69 ms-2.31 s) for these gases at room temperature due to the effective surface diffusion at 300 K. Consequently, the FeCrPc and FeMnPc materials can be utilized as high-performance, reusable gas sensors for detecting C2H4 and H2CO, and have promising applications in monitoring the release of ethylene and formaldehyde from industrial processes.

Squalene Depletion in Skin Following Human Exposure to Ozone under Controlled Chamber Conditions

A major component of human skin oil is squalene, a highly unsaturated hydrocarbon that protects the skin from atmospheric oxidants. Skin oil, and thus squalene, is continuously replenished on the skin surface. Squalene is also quickly consumed through reactions with ozone and other oxidants. This study examined the extent of squalene depletion in the skin oils of the forearm of human volunteers after exposure to ozone in a climate chamber. Temperature, relative humidity (RH), skin coverage by clothing, and participants' age were varied in a controlled manner. Concentrations of squalene were determined in skin wipe samples collected before and after ozone exposure. Exposures to ozone resulted in statistically significant decreases in post-exposure squalene concentrations compared to pre-exposure squalene concentrations in the skin wipes when squalene concentrations were normalized by concentrations of co-occurring cholesterol but not by co-occurring pyroglutamic acid (PGA). The rate of squalene loss due to ozonolysis was lower than its replenishment on the skin surface. Within the ranges examined, temperature and RH did not significantly affect the difference between normalized squalene levels in post-samples versus pre-samples. Although not statistically significant, skin coverage and age of the volunteers (three young adults, three seniors, and three teenagers) did appear to impact squalene depletion on the skin surfaces.

Investigating the spatial distribution of volatile organic compounds in aircraft cabins from various emission sources

Volatile organic compounds (VOCs) significantly affect the air quality in aircraft cabins, consequently affecting passenger health and comfort. Although VOC emission sources and their contributions have been studied extensively, the distribution characteristics of VOCs originating from diverse sources within cabins have received limited attention, and the correlation between VOC sources and concentrations in passenger breathing zones remains largely unexplored. To fill this knowledge gap, the concentration field of VOCs was investigated using a computational fluid dynamics model, and the results were experimentally validated in a typical single-aisle aircraft cabin with seven seat rows. The diffusion characteristics of different VOCs emitted by four typical sources in aircraft cabins (floors, human surfaces, seats, and respiratory sources) were analyzed and compared. The distribution of VOCs emitted by different sources was nonuniform and could be classified into two distinct categories. When the emission intensities of all sources were equal, the average concentration of VOCs emitted from the floor source were considerably lower in the passenger breathing zone (4.01 μg/m³) than those emitted from the human surface, seat, and respiratory sources, which exhibited approximately equal concentrations (6.82, 6.90, and 7.29 μg/m³, respectively). The analysis highlighted that the simplified lumped-parameter method could not accurately estimate the exposure concentrations within an aircraft cabin. To address this issue, we propose a correction method based on the emission intensity of each VOC source. This study provides critical insights into the diffusion characteristics of VOCs within aircraft cabins and VOC emissions from various sources.

Emissions of Volatile Organic Compounds from Human Occupants in a Student Office: Dependence on Ozone Concentration

Human occupants themselves constitute an important source of volatile organic compounds (VOCs) in indoor environments through breath and dermal emissions. In order to quantify VOC emissions from occupants under real-world settings, previous indoor observational studies often determined emission factors (i.e., average emission rates per person). However, the values obtained across these studies exhibited large variability, and the causes of this variability still need to be understood. Herein we report 10-day real-time VOC measurements in a university student office, using a proton transfer reaction-quadrupole interface-time-of-flight mass spectrometer. A method was developed to identify VOCs of primary human origin and to quantify the corresponding emission factors, accounting for the dynamically changing occupancy level and ventilation rate in the assessed office. We found that the emission factors of many dermally emitted VOCs strongly increased as the ozone concentration increased from <3 to 10-15 ppb. These VOCs include geranyl acetone, 6-methyl-5-hepten-2-one (6-MHO), and C10-C12 saturated aldehydes, which align with characteristic first-generation ozonolysis products of skin oil. The strongest increase occurred for 6-MHO, from 113 to 337 μg/h/p. In comparison, acetone and isoprene, which are primarily emitted from human breath, varied little with the ozone level. In light of this finding, we conducted an integrated analysis of emission factors reported in the literature for two frequently reported species, namely, 6-MHO and decanal. Ozone concentration alone can explain 94-97% of the variation in their emission factors across previous studies, and the best-estimated ozone dependence obtained using the literature data is consistent with those obtained in the current study. These results suggest that the ozone concentration is a key factor regulating emission factors of many dermally emitted VOCs in real indoor environments, which has to be considered when reporting or using the emission factors.