Abstract
This study aimed to better understand and quantify the influence of ventilation strategies on occupant‐related indoor air chemistry. The oxidation of human skin oil constituents was studied in a continuously ventilated climate chamber at two air exchange rates (1 h−1 and 3 h−1) and two initial ozone mixing ratios (30 and 60 ppb). Additional measurements were performed to investigate the effect of intermittent ventilation (“off” followed by “on”). Soiled t‐shirts were used to simulate the presence of occupants. A time‐of‐flight‐chemical ionization mass spectrometer (ToF‐CIMS) in positive mode using protonated water clusters was used to measure the oxygenated reaction products geranyl acetone, 6‐methyl‐5‐hepten‐2‐one (6‐MHO) and 4‐oxopentanal (4‐OPA). The measurement data were used in a series of mass balance models accounting for formation and removal processes. Reactions of ozone with squalene occurring on the surface of the t‐shirts are mass transport limited; ventilation rate has only a small effect on this surface chemistry. Ozone‐squalene reactions on the t‐shirts produced gas‐phase geranyl acetone, which was subsequently removed almost equally by ventilation and further reaction with ozone. About 70% of gas‐phase 6‐MHO was produced in surface reactions on the t‐shirts, the remainder in secondary gas‐phase reactions of ozone with geranyl acetone. 6‐MHO was primarily removed by ventilation, while further reaction with ozone was responsible for about a third of its removal. 4‐OPA was formed primarily on the surfaces of the shirts (~60%); gas‐phase reactions of ozone with geranyl acetone and 6‐MHO accounted for ~30% and ~10%, respectively. 4‐OPA was removed entirely by ventilation. The results from the intermittent ventilation scenarios showed delayed formation of the reaction products and lower product concentrations compared to continuous ventilation.
Highlights
The importance of indoor air chemistry has been increasingly rec‐ ognized over the past decades.[1,2,3,4] Building materials, furnishings and carpeting, cleaning products, personal care products, human activi‐ ties, as well as outdoor air have been considered major sources of indoor air pollutants
Having six carbon‐car‐ bon double bonds in its structure, squalene serves as a natural antioxidant to protect our skin from atmospheric oxidants such as ozone (O3), which reacts with the unsaturated sites of the mol‐ ecule
The branching ratios for 6‐MHO and 4‐OPA from the gas‐phase reaction of ozone and geranyl acetone (GA) are unknown; we have set the value of f6MHO to 0.3 in accordance with the findings described by Grosjean and Grosjean (1997).[31]
Summary
The importance of indoor air chemistry has been increasingly rec‐ ognized over the past decades.[1,2,3,4] Building materials, furnishings and carpeting, cleaning products, personal care products, human activi‐ ties, as well as outdoor air have been considered major sources of indoor air pollutants. There has been grow‐ ing recognition that humans themselves considerably contribute to indoor air pollution and impact indoor air chemistry.[5,6]. Squalene constitutes approximately 12% (by weight) of human skin lipids; other constituents include fatty acids, glycerides, wax esters, ceramides, and cholesterol esters.[7] Having six carbon‐car‐ bon double bonds in its structure, squalene serves as a natural antioxidant to protect our skin from atmospheric oxidants such as ozone (O3), which reacts with the unsaturated sites of the mol‐ ecule. Squalene is responsible for about half of all unsaturations available in skin lipids,[8] and given the slight differences in reac‐ tion probabilities between unsaturations in squalene and fatty acids and their esters, it is responsible for approximately half the ozone uptake
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