The oxidation of organics adsorbed on surfaces by ozone is of fundamental chemical interest and potentially important in the lower atmosphere. Studies of the oxidation of the three-carbon and eight-carbon vinylterminated self-assembled monolayers (SAMs, C3d and C8d) on a silicon ATR (attenuated total reflectance) crystal by gas-phase O 3 at 296 K are reported. Oxidation of the SAMs was followed in real time by ATR-FTIR using ozone concentrations that spanned 5 orders of magnitude, from ∼10 11 to 10 16 molecules cm -3 . For comparison, some studies of the saturated C8 SAM were also carried out. The films were also characterized by atomic force microscopy and water contact angle measurements. The loss of CdC and the formation of CdO were measured in real time and shown to be consistent with a Langmuir-Hinshelwood mechanism in which O 3 is rapidly adsorbed on the surface and then reacts more slowly with the alkene moiety. This is supported by molecular dynamics (MD) calculations which show that O 3 does not simply undergo elastic collisions but has a significant residence time on the surface. However, the kinetics measurements indicate a much longer residence time than the MD calculations, suggesting a chemisorption of O 3 . Formaldehyde was observed as a gas-phase product by infrared cavity ring down spectroscopy. Possible mechanisms of the ozonolysis and its atmospheric implications are discussed.

We quantify the NO 2 fluxes released into the gas phase during the continuous λ ∼ 300 nm photolysis of NO 3in submillimeter ice layers produced by freezing aqueous KNO 3 sprays on cold surfaces. Fluxes, F NO 2 , increase weakly with [NO 3 -] between 5 e [NO 3 -]/mM e 50 and increase markedly with temperature in the range of 268 g T/K g 248. We found that F NO 2 , the photostationary concentration of NO 2 -(another primary photoproduct), and the quantum yield of 2-nitrobenzaldehyde in situ photoisomerization are nearly independent of ice layer thickness d within 80 e d/µm e 400. We infer that radiation is uniformly absorbed over the depth of the ice layers, where NO 3is photodecomposed into NO 2 (+ OH) and NO 2 -(+ O), but that only the NO 2 produced on the uppermost region is able to escape into the gas phase. The remainder is trapped and further photolyzed into NO. We obtain φ NO 2 -∼ 4.8 × 10 -3 at 263 K, i.e., about the quantum yield of nitrite formation in neutral NO 3aqueous solutions, and an apparent quantum yield of NO 2 release φ′ NO 2 ∼ 1.3 × 10 -3 that is about a factor of 5 smaller than solution φ OH data extrapolated to 263 K. These results suggest that NO 3photolysis in ice takes place in a liquidlike environment and that actual φ′ NO 2 values may depend on the morphology of ice deposits. Present φ′ NO 2 data, in conjunction with snow albedo and absorptivity data, lead to F NO 2 values in essential agreement with recent measurements in Antarctic snow under solar illumination.

A number of heterogeneous reactions of atmospheric importance occur in thin water films on surfaces in the earth's boundary layer. It is therefore important to understand the interaction of water with various materials, both those used to study heterogeneous chemistry in laboratory systems, as well as those found in the atmosphere. We report here studies at 22 C to characterize the interaction of water with such materials as a function of relative humidity from 0-100%. The surfaces studied include borosilicate glass, both untreated and after cleaning by three different methods (water, hydrogen peroxide and an argon plasma discharge), quartz, FEP Teflon film, a self assembled monolayer of n-octyltrichlorosilane (C8 SAM) on glass, halocarbon wax coatings prepared by two different methods, and several different types of Teflon coatings on solid substrates. Four types of measurements covering the range from the macroscopic level to the molecular scale were made: (1) contact angle measurements of water droplets on these surfaces to obtain macroscopic scale data on the water-surface interaction, (2) atomic force microscopy measurements to provide micron to sub-micron level data on the surface topography, (3) transmission FTIR of the surfaces in the presence of increasing water vapor concentrations to probe the interaction with the surface at a molecular level, and (4) X-ray photoelectron spectroscopy measurements of the elemental surface composition of the glass and quartz samples. Both borosilicate glass and the halocarbon wax coatings adsorbed significantly more water than the FEP Teflon film, which can be explained by a combination of the chemical nature of the surfaces and their physical topography. The C8 SAM, which is both hydrophobic and has a low surface roughness, takes up little water. The implications for the formation of thin water films on various surfaces in contact with the atmosphere, including building materials, soil, and vegetation, are discussed.

The quantum yield, φ, of nitrite formation in the 302 nm band photolysis of fluid or frozen aqueous nitrate solutions increases monotonically with temperature over the range 238-294 K. The presence of formate increases φ 5-fold but does not modify its temperature dependence. Considering that the detection of nitrite as a product is only possible after the initial photofragments (NO 2 -+ O) escape the solvent cage and that the diffusivity of ice, D ice , is about 6 orders of magnitude smaller than that of supercooled water, D aq , at the same temperature, we infer that nitrate photodecomposition takes place in similar liquidlike media at all temperatures. We found that the nitrite dispersed into the bulk is subsequently degraded by OH radicals, another primary photoproduct that can be scavenged by formate. The fact that experimental φ values in ice are actually larger than those derived from linear φ vs D aq T 1/2 extrapolation of aqueous phase data, as expected for cage processes in homogeneous media, suggests that the photochemically relevant properties of the quasi-liquid layer covering ice below the normal melting point resemble those of bulk supercooled water, but other effects, such as the dissipation of excess photon energy into the medium, may also play a role.

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.