UBC Theses and Dissertations
Indoor ozone chemistry causes changes in phase behavior of indoor organic films containing unsaturated lipids Xu, Zhenyang
The reactions between ozone and indoor unsaturated lipid films leads to the formation of products with negative health effects. Although much work has been conducted to study the ozone chemistry in unsaturated lipid films, little research has focused on the phase behavior of the films during ozonolysis, which is critical in understanding the kinetics and effects of the corresponding reactions. Here we show that a second phase will form during the ozonolysis of six kinds of unsaturated lipid droplets relevant for indoors (squalene, triolein, oleic acid, a skin oil proxy and canola oil) after several hours of exposure to 700-850 ppb of ozone under two different relative humidity (RH) ranges, 4.5 -6.5 % and 50 -65 %. For triolein, oleic acid and canola oil, a clear second phase formed under the same exposure time regardless of the RH, while an extended exposure time was required to form a second phase for squalene and a skin oil proxy at higher RH compared to low RH. Subsequent melting tests showed that the temperatures for the onset and completion of melting of the second phase were higher for the droplets oxidized at low RH compared to those oxidized at higher RH. Oligomers and polymers formed from secondary ozonolysis reactions are proposed as key components of the second phase. Finally, our observations were used to predict the formation of a second phase in real indoor organic films. Our work suggests that a second phase is most likely to form in skin oil films and cooling oil films indoors due to ozonolysis.
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