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The adsorption of citric acid onto Ti[O.sub.2] anatase nanoparticles is examined at circumneutral and acidic pHs, where the analysis has focused on the surface chemistry of citric acid on Ti[O.sub.2], including measurements of surface coverage and speciation, and its impact on nanoparticle behavior. The results have shown that surface coverage is a function of pH and has decreased with increasing pH, whereas surface speciation has differed from the bulk solution and is time dependent.

The role of solvation in the photochemistry of adsorbates at solid interfaces and the impact of molecular oxygen, adsorbed water and relative humidity in photochemical processes on aerosol surfaces that have the potential to alter the chemical balance of the atmosphere are examined. The results have shown that the photolysis of adsorbed nitrate on mineral dust aerosol, as nitrate in organic films, have played a vital role in the chemistry of the atmosphere through renoxification.

Several experiments are conducted to explain the heterogeneous and multiphase chemistry and photochemistry of mineral dust aerosol, which forms a large fraction of the tropospheric aerosol. The aerosol is shown to constitute mainly of oxides, clays and carbonates.

The impact of ocean microbiological activity on the chemical species present in the sea surface microlayer (SSML) was investigated using attenuated total reflection-Fourier transform infrared (ATR-FT-IR) spectroscopy. We observe clear [...]

The ATR-FTIR and UV/vis spectra of concentrated nitrate solutions are measured over a large concentration range to gain a better understanding of the nitrate ion chromophore in concentrated aqueous nitrate aerosols. It is found that both ATR-FTIR and UV/vis spectroscopy shows change in the nitrate ion spectra with increasing concentration.

A kinetic study of heterogeneous ozone decomposition aerosols was conducted to better understand the role of mineral dust aerosol in ozone loss mechanisms in the atmosphere. Increasing the relative humidity (RH) resulted in strong decrease in the measured ozone uptake up to the highest RH investigated for both samples with the water coverage of approximately 2-3 monolayers.

Aspects of the importance of aqueous nitrate aerosols are reviewed and a multi-analysis aerosol reactor system that is used to measure the physicochemical properties of these atmospherically relevant aerosols is described. The results presented show that physical chemistry measurements of atmospherically relevant aerosols are essential if aerosols, an important component of the Earth's atmosphere, can be fully understood.

The chemistry of carbon dioxide at the adsorbed water iron-oxide interface is investigated. Adsorbed water enhances CO2 uptake, undergoes isotope exchange with CO2 in O(18)-labeled experiments, and influences the chemical nature of the predominant adsorbed product on the surface from bicarbonate to carbonate.

There is great concern regarding the adverse health implications of engineered nanoparticles. However, there are many circumstances where the production of incidental nanoparticles, i.e., nanoparticles unintentionally generated as a side product of some anthropogenic process, is of even greater concern. In this study, metal-based incidental nanoparticles were measured in two occupational settings: a machining center and a foundry. On-site characterization of substrate-deposited incidental nanoparticles using a field-portable X-ray fluorescence provided some insights into the chemical characteristics of these metal-containing particles. The same substrates were then used to carry out further off-site analysis including single-particle analysis using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Between the two sites, there were similarities in the size and composition of the incidental nanoparticles as well as in the agglomeration and coagulation behavior of nanoparticles. In particular, incidental nanoparticles were identified in two forms: submicrometer fractal-like agglomerates from activities such as welding and supermicrometer particles with incidental nanoparticles coagulated to their surface, herein referenced as nanoparticle collectors. These agglomerates will affect deposition and transport inside the respiratory system of the respirable incidental nanoparticles and the corresponding health implications. The studies of incidental nanoparticles generated in occupational settings lay the groundwork on which occupational health and safety protocols should be built. [ABSTRACT FROM AUTHOR]

Iron-containing mineral aerosols play a key role in the oxidation of sulfur species in the atmosphere. Simulated cloud processing (CP) of typical mineral particles, such as illite (IMt-2), nontronite (NAu-2), smectite (SWy-2) and Arizona test dust (ATD) is shown here to modify sulfur dioxide (SO2) uptake onto mineral surfaces. Heterogeneous oxidation of SO2 on particle surfaces was firstly investigated using an in situ DRIFTS apparatus. Our results showed that the BET surface area normalized uptake coefficients (γBET) of SO2 on the IMt-2, NAu-2, SWy-2 and ATD samples after CP were 2.2, 4.1, 1.5 and 1.4 times higher than the corresponding ones before CP, respectively. The DRIFTS results suggested that CP increased the amounts of reactive sites (e.g., surface OH groups) on the particle surfaces and thus enhanced the uptake of SO2. TEM showed that the particles broke up into smaller pieces after CP, and thus produced more active sites. The free-Fe measurements confirmed that more reactive Fe species were present after CP, which could enhance the SO2 uptake more effectively. Mössbauer spectroscopy further revealed that the formed Fe phase were amorphous Fe(III) and nanosized ferrihydrite hybridized with Al/Si, which were possibly transformed from the Fe in the aluminosilicate lattice. The modification of Fe speciation was driven by the pH-dependent fluctuation coupling with Fe dissolution-precipitation repeatedly during the experiment. Considering both the enhanced SO2 uptake and subsequent promotion of iron dissolution along with more active Fe formation, which in turn lead to more SO2 uptake, it was proposed that there may be a positive feedback between SO2 uptake and iron mobilized on particle surfaces during CP, thereby affecting climate and biogeochemical cycles. This self-amplifying mechanism generated on the particle surfaces may also serve as the basis of high sulfate loading in severe fog-haze events observed recently in China. [ABSTRACT FROM AUTHOR]

The structures of cis-1,2- and trans-1,2-dichloroethene (DCE) adsorbed on the Pt(111) surface have been examined by electron energy loss and thermal desorption spectroscopies over the temperature range 110 to 300 K. For monolayer and submonolayer coverages, the DCEs form sigma bonds to the platinum surface and assume staggered, alkane-like structures. Cis-DCE gives the gauche isomer with its most intense EEL peaks at 650 and 2985 cm-1, while the trans-DCE gives the trans conformer with its most intense peaks at 720 and 3000 cm-1. Isomerization does not occur. On warming to 160 K, the multilayer desorbs and above 200 K, dehalogenation occurs. A prominent EEL peak around 290 cm-1 shows that the chlorine atoms remain bonded to the surface. For both cis- and trans-DCE, the remainder of the EEL spectrum is that of C2H2 bonded to the surface in an olefinic structure signaled by prominent peaks at 770–785 and 3010–3020 cm-1. [ABSTRACT FROM AUTHOR]

The photochemical behaviors of cis- and trans-1,2-dichloroethene (DCE) adsorbed on Pd(111) and Pt(111) surfaces have been studied using electron energy loss spectroscopy (EELS). For multilayer coverage on either metal surface, irradiation of physisorbed DCE at 110 K with broad band irradiation (λ>200 nm) results in photoisomerization, cis–trans. For monolayer coverage on Pt(111) at 110 K, photolysis of chemisorbed DCE causes loss of the two chlorine atoms to form a single hydrocarbon product, chemisorbed acetylene. Apparently, for λ>237 nm, the chlorine atoms remain bound to the platinum surface whereas for shorter wavelengths, λ>200 nm, the chlorine atoms leave the surface. These results are interpretable in terms of singlet excitation of the chemisorbed alkane followed by chlorine elimination on an excited singlet reaction surface. This study indicates that photochemistry of molecules chemisorbed on a metal surface is possible despite the proximity of the conducting surface. It shows that energy relaxation processes connected with this proximity are not prohibitively fast. [ABSTRACT FROM AUTHOR]