Heterogeneous oxidation of squalene film by ozone under various indoor conditions

Abstract

The effects of indoor conditions (ozone concentration, temperature, relative humidity (RH), and the presence of NO(x)) on heterogeneous squalene oxidation were studied with Attenuated Total Reflectance-Fourier Transform Infrared spectroscopy. The heterogeneous kinetics of squalene-ozone reaction revealed a pseudo-first-order reaction rate constant of 1.22 x 10(-5)/s at [O(3)] = 40 ppb. Oxidation kinetics were insensitive to temperature over the range of 24-58 +/- 2 degrees C as well as to RH and presence of NO(x). Products, however, were affected by the environmental parameters. As temperature was increased, fewer surface products and more low molecular weight gaseous products were observed. Lower air exchange rates also enhanced gas phase reactions, allowing for formation of secondary gas phase products. As RH increased, there was a shift in product distribution from ketones to aldehydes, and the presence of NO(x) during squalene ozonolysis resulted in the formation of nitrated oxidation products. Identified surface products included 6-methyl-5-hepten-2-one, geranyl acetone, and long chain ketones and aldehydes, while gas phase products included formaldehyde, acetone, 4-oxopentanal (4-OPA), glyoxal, and pyruvic acid. Practical Implications Heterogeneous oxidation of squalene resulted in surface products including long chain aldehydes and ketones, and gas phase products including formaldehyde, a known human carcinogen (IARC 2006), and bicarbonyl compounds like: 4-oxopentanal (4-OPA), glyoxal, and pyruvic acid that are characterized as asthma triggers and sensitizers (Anderson et al., 2007; Jarvis et al., 2005). In addition, ozonolysis experiments in the presence of NO(x) showed the formation of nitrated surface oxidation products. Such nitrated products may have higher mutagenicity, carcinogenicity, or allergenic potential than their nitrate free counterparts (Franze et al., 2005; Pitts, 1983). Kinetic studies determined that at moderate ozone levels of 40 ppb (Uhde and Salthammer, 2007), and an estimated skin surface density of 4 x 10(15) molecules/cm(2), surface reaction would lead to a minimum product formation flux of 4 x 10(10) molecules cm(2)/s. As squalene is naturally occurring and continually produced by the human body, its concentration in the indoor environment cannot be controlled. However, this study highlights the importance of regulating air exchange rate, temperature, and ozone level in the indoor environment on the formation of potentially harmful or irritating squalene oxidation products.

Dynamic viscosity mapping of the oxidation of squalene aerosol particles

“…28 Therefore it is found in detectable concentrations within aerosol in cities and urban areas. 29,30 In the presence of strong oxidants such as ozone, squalene yields high molecular weight products such as polyunsaturated aldehydes, similar to those found in the very complex naturally occurring secondary organic aerosols (SOA) in the atmosphere 27,31 . The initial step of squalene ozonolysis will be via the well-known Criegee mechanism which generates carbonyls and carbonyl oxides also known as "Criegee intermediates" via a primary ozonide.…”

“…Squalene is a 30-carbon naturally occurring triterpene ( Figure S1, ESI) which herein we use as a model organic aerosol. It has a vital role in the synthesis of sterols in animals and plants 23,24 and is also produced by human skin 25,26 and found as an ingredient in many household oils, used for cooking and frying 27 . Due to skin shedding (desquamation), squalene containing skin flakes are likely a major constituent of indoor dust and hence aerosol.…”

“…The initial step of squalene ozonolysis will be via the well-known Criegee mechanism which generates carbonyls and carbonyl oxides also known as "Criegee intermediates" via a primary ozonide. 32 Known squalene ozonolysis products contain many functional groups, such as ketones, alcohols, hydroperoxides and carboxylic acids also found in SOA in the atmosphere 26,27,33 . A high resolution mass spectrometry study showed that over 1300 products are generated from squalene ozonolysis and the accompanying model predicts many more are possible which indicates the complexity of the system.…”

Tobacco smoke aging in the presence of ozone: A room-sized chamber study

“…While some homogenous gas phase reactions are important indoors, the available experimental evidence indicates that the most important decay processes for indoor ozone involve surface reactions that are major sources of secondary pollutants (Morrison and Nazaroff 2002;Aoki and Tanabe 2007;Zhao et al 2007) and sorbed chemicals (Fan et al 2003;Fick et al 2005;Singer et al 2006;Wang and Morrison 2006;Coleman et al 2008;Petrick and Dubowski 2009). The characterization of ozone-initiated chemical reactions on indoor surfaces will contribute to understanding their link to health effects 5 and provide important insights into design of effective engineering solutions that eliminate or reduce exposure to toxic chemicals generated by these reactions (Weschler 2004;Weschler and Wells 2004;Weschler 2006;Morrison 2008).…”

Heterogeneous chemistry and reaction dynamics of the atmospheric oxidants, O3, NO3, and OH, on organic surfaces

“…Additionally, attenuated total reflectance infrared (ATR-IR) experiments [75][76][77][78] have been used to investigate the effects of temperature, [75][76][77] relative humidity, [75][76][77] and film thickness 77 on reaction mechanisms, 76 product yields, 76,78 product hygroscopicity, 75,77,78 and redox activity. 75 As ATR-IR allows for in situ collection of infrared spectra, the change in the IR intensity of specific vibrational modes during exposure can be used to obtain kinetic information such as ozone's reactive uptake coefficient, which has been determined to be in the range of 1.0 Â 10 À5 , 76 to 5.1 Â 10 À4 . 75 The measured variations in ozone uptake coefficients are likely related to differences in the reaction conditions, surface properties, and the particular infrared band analyzed to extract kinetic information.…”