Modeling the Time-Dependent Concentrations of Primary and Secondary Reaction Products of Ozone with Squalene in a University Classroom

Abstract

Volatile organic chemicals are produced from reactions of ozone with squalene in human skin oil. Both primary and secondary reaction products, i.e., 6-methyl-5-hepten-2-one (6-MHO) and 4oxopentanal (4-OPA), have been reported in indoor occupied spaces. However, the abundance of these products indoors is a function of many variables, including the amount of ozone and occupants present as well as indoor removal processes. In this study, we develop a timedependent kinetic model describing the behavior of ozone/squalene reaction products indoors, including the reaction process and physical adsorption process of products on indoor surfaces. The key parameters in the model were obtained by fitting time-resolved concentrations of 6-MHO, 4-OPA, and ozone in a university classroom on 1 day with multiple class sessions. The model predictions were subsequently tested against observations from four additional measurement days in the same classroom. Model predictions and experimental data agreed well (R 2 = 0.87−0.92) for all test days, including ∼7 class sessions covering a range of occupants (10−70) and ozone concentrations (0.09−32 ppb), demonstrating the effectiveness of the model. Accounting for surface uptake of 6-MHO and 4-OPA significantly improved model predictions (R 2 = 0.52−0.76 without surface uptake), reflecting the importance of including surface interactions to quantitatively represent product behavior in indoor environments.

Observing ozone chemistry in an occupied residence

“…Second, occupants might dynamically alter indoor ozone reactivity via their time-dependent presence indoors as well as their intended and unintended activities such as desquamation, transferring skin oils to surfaces by direct contact, cooking (e.g., surface soiling by the deposition of fatty acids in cooking oils and foods), and cleaning (e.g., with products that contain ozone-reactive terpenoids). Indoor studies in densely occupied spaces, including in two classrooms, a simulated office, and a simulated aircraft cabin (14,(21)(22)(23), have all highlighted the importance of the direct presence of human occupants for ozone chemistry.…”

The role of computational fluid dynamics tools on investigation of pathogen transmission: Prevention and control

“…Moreover, Cuce et al (2019) studied the natural ventilation in school buildings based on its working principles and limitation of passive ventilation; In a crowded room, the concentration of volatile organic substances generated by human skin oil is high, Xiong et al (2019) analyzed the concentration change of products from reactions of ozone with squalene in a University classroom. The CFD method was used, and the time-dependent concentration of chemicals in the classroom was defined in simulation.…”

Investigation of indoor total volatile organic compound concentrations in densely occupied university buildings under natural ventilation: Temporal variation, correlation and source contribution

“…However, the total indoor emission rates were initially increased during the first stage, and then became relatively stable in the case of unchanged number of occupants with the exception of sudden indoor sources, whereas TVOC concentrations rose steadily (as shown in Figure 3). The multiple processes were expected to lead to a variation in the total indoor emission rates, such as skin and breathing emissions, 7–10 ozonation, 11,12 use of personal care products, 32 etc. At the end of indoor activities, both indoor emission rates and TVOC concentrations declined due to the reduced occupancy rate and the increase in ventilation rate, as the doors were open whenever occupants left the room.…”

“…5 Humans could generate VOCs through their 'natural' emissions via skin 7,8 or breath, 9,10 as well as other chemical processes. 11,12 In particular, the reaction of ozone with the oil secreted by humans (which remains on the hair and clothing) may serve as a source of indoor VOCs. 11,12 Moreover, researchers have also studied certain VOC species and their concentration ranges in education buildings.…”

“…11,12 In particular, the reaction of ozone with the oil secreted by humans (which remains on the hair and clothing) may serve as a source of indoor VOCs. 11,12 Moreover, researchers have also studied certain VOC species and their concentration ranges in education buildings. They have identified potential factors, such as outdoor pollutant levels, 13 building function 14 and seasons 15 that could influence the VOC species and their concentration levels due to differences in materials, temperature, ventilation, etc.…”