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

Abstract

Ozone reactions on human body surfaces produce volatile organic compounds (VOCs) that influence indoor air quality. However, the dependence of VOC emissions on the ozone concentration has received limited attention. In this study, we conducted 36 sets of single-person chamber experiments with three volunteers exposed to ozone concentrations ranging from 0 to 32 ppb. Emission fluxes from human body surfaces were measured for 11 targeted skin-oil oxidation products. For the majority of these products, the emission fluxes linearly correlated with ozone concentration, indicating a constant surface yield (moles of VOC emitted per mole of ozone deposited). However, for the second-generation oxidation product 4-oxopentanal, a higher surface yield was observed at higher ozone concentrations. Furthermore, many VOCs have substantial emissions in the absence of ozone. Overall, these results suggest that the complex surface reactions and mass transfer processes involved in ozone-dependent VOC emissions from the human body can be represented using a simplified parametrization based on surface yield and baseline emission flux. Values of these two parameters were quantified for targeted products and estimated for other semiquantified VOC signals, facilitating the inclusion of ozone/skin oil chemistry in indoor air quality models and providing new insights on skin oil chemistry.

Ozone Loss: A Surrogate for the Indoor Concentration of Ozone-Derived Products

“…Most of the Yield gas values in Table are dominated by products of the ozone/skin oil chemistry: 16 “passengers” in a 28 m 3 simulated aircraft cabin, 2 occupants in a sparsely furnished 28 m 3 simulated office, 4 volunteers in a 22 m 3 chamber, and a single occupant in a very small (1.5 m 3 ) chamber . The major products contributing to Yield gas in these studies were acetone, 6-MHO, 4-OPA, decanal, nonanal, nonenal, and acetic acid.…”

“…Liu et al 30 found that in measurements made with a PTR-MS in a normally occupied residence over an 8-week period, the concentrations of several ozone-derived products scaled in a roughly linear fashion with the indoor ozone concentration (See Figure 3 of the cited paper.). In a chamber study of products resulting from ozone reactions with human surfaces, Qu et al 47 observed that for most volatile products resulting from indoor ozone reactions, there was a linear relationship between emission rates and ozone concentration. Byproduct concentrations would be proportional to byproduct emission rates if byproduct loss from indoor air occurs only by ventilation and there are no other meaningful emission sources, including outdoor air.…”

“…Byproduct concentrations would be proportional to byproduct emission rates if byproduct loss from indoor air occurs only by ventilation and there are no other meaningful emission sources, including outdoor air. For the products noted in the Qu et al 47 study, these conditions were met.…”

“…Such yields are anticipated to vary with experimental conditions. 55 The yields reported by Qu et al 47 are true surface yields (i.e., net moles of gaseous product emitted per mole of ozone consumed in a surface reaction) and are less sensitive to experimental parameters. The yields from Weschler et al, 8 Arata et al, 56 and Morrison et al 57 are close to surface yields since the high air-change rates used in these studies allowed little time for gas-phase chemistry.…”

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

“…Even for these two reactions, some parameters have not been measured directly. In this study we followed the approach used in our recent chamber study for parametrization and represented the reactions as follows 6 ‐MHO + normalO 3 → k 6 − MHO 0.3 .25em acetone + 0.8 .25em 4 ‐OPA GA + normalO 3 → k GA 0.15 .25em 6 ‐MHO + 0.4 .25em 4 ‐OPA + 0.15 .25em acetone + 0.4 .25em 4 ‐MON where k 6‑MHO and k GA are the ozone reaction rate coefficient with 6-MHO and geranyl acetone, respectively. They were assigned values of 0.035 and 0.070 ppb –1 h –1 .…”