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

Integrating Sacrificial Bonds into Dynamic Covalent Networks toward Mechanically Robust and Malleable Elastomers

Vitrimers are a class of covalently cross-linked polymers that have drawn great attention due to their fascinating properties such as malleability and reprocessability. The state of art approach to improve their mechanical properties is the addition of fillers, which, however, greatly restricts the chain mobility and impedes network topology rearrangement, thereby deteriorating the dynamic properties of vitrimer composites. Here, we demonstrate that the integration of sacrificial bonds into a vitrimeric network can remarkably enhance the overall mechanical properties while facilitating network rearrangement. Specifically, commercially available epoxidized natural rubber is covalently cross-linked with sebacic acid and simultaneously grafted with N-acetylglycine (NAg) through the chemical reaction between epoxy and carboxyl groups, generating exchangeable β-hydroxyl esters and introducing amide functionalities into the networks. The hydrogen bonds arising from amide functionalities act in a sacrificial and reversible manner, that is, preferentially break prior to the covalent framework and undergo reversible breaking and reforming to dissipate mechanical energy under external load, which leads to a rarely achieved combination of high strength, modulus, and toughness. The topology rearrangement of the cross-linked networks can be accomplished through transesterification reactions at high temperatures, which is accelerated with the increase of grafting NAg amount due to the dissociation of transient hydrogen bonds and increase of the ester concentration in the system

Speed of kill with HT61 against non-multiplying MSSA and MRSA.

<p>HT61 was incubated with MSSA (A) and MRSA (B) at different concentrations for 24 hours. At different time points, CFU counts were performed.</p

The MSC₅₀ and MIC of HT61 against clinically isolated MRSA, VISA and VRSA.

<p>The MSC₅₀ and MIC of HT61 against clinically isolated MRSA, VISA and VRSA.</p

Effect of HT61 against MSSA and MRSA in a murine skin bacterial colonization model.

<p>Stationary phase MSSA (A) and MRSA (B) were applied onto 2 cm² skin area followed by addition of HT61 gel, Bactroban and placebo (control) for 2 hours. Log phase MSSA were treated with HT61 gel, Bactroban and placebo (control) for 2 hours on mouse skin (C). The data has been repeated twice.</p

Effect of HT61 against MSSA and MRSA in a murine skin bacterial infection model.

<p>A. After tape-stripping the skin, log phase MSSA was applied onto the skin area. At different time points CFU counts of the bacteria were determined. The arrow indicates the point which the treatment was initiated. B. Treatment of HT61, Bactroban and placebo (control) against MSSA and C. Treatment of HT61, Bactroban and placebo (control) against MRSA. **, P<0.01. The data has been repeated twice.</p

HT61-induced cytoplasmic membrane permeabilization determined by the DiSC3(5) assay.

<p>Non-multiplying and log phase MSSA were incubated with DiSC3(5) to a final concentration of 0.4 mM until no more quenching was detected, which was followed by addition of 0.1 M KCl. Different concentrations of HT61 were incubated with non-multiplying MSSA (A) and log phase MSSA (B). The changes in fluorescence were monitored at various time points. The data was confirmed in two independent experiments.</p

Thin sectioned electron micrographs of <i>S. aurues</i> analyzed by transmission electron microscopy.

<p>The cells were fixed 10 minutes after HT61 treatment. A. normal <i>S. aureus</i> cells. B. HT61 at 10 µg/ml. C. HT61 at 20 µg/ml. D. HT61 at 40 µg/ml. The scale bar is 0.2 µm.</p

Effects of HT61 against stationary phase non-multiplying <i>S. pyogenes</i>, S. <i>agalactiae</i>, <i>S. epidermidis</i> and <i>P. acnes</i>.

<p>HT61 was added to the non-multiplying cultures at 20, 10, 5 and 0 µg/ml. CFU counts were carried out after 24 hours of incubation. These results were confirmed in two independent experiments.</p

Growth curves of methicillin-sensitive and methicillin-resistant <i>S. aureus</i>.

<p>The bacterium was grown in nutrient broth medium with shaking for 10 days. The arrows indicate the timepoints when the cultures were used for drug sensitivity test. These results were confirmed in two independent experiments.</p