In this study, iron solubility from six combustion source particles was investigated in acidic media. For comparison, a Chinese loess (CL) dust was also included. The solubility experiments confirmed that iron solubility was highly variable and dependent on particle sources. Under dark and light conditions, the combustion source particles dissolved faster and to a greater extent relative to CL. Oil fly ash (FA) yielded the highest soluble iron as compared to the other samples. Total iron solubility fractions measured in the dark after 12 h ranged between 2.9 and 74.1% of the initial iron content for the combustion-derived particles (Oil FA > biomass burning particles (BP) > coal FA). Ferrous iron represented the dominant soluble form of Fe in the suspensions of straw BP and corn BP, while total dissolved Fe presented mainly as ferric iron in the cases of oil FA, coal FA, and CL. Mössbauer measurements and TEM analysis revealed that Fe in oil FA was commonly presented as nanosized Fe(3)O(4) aggregates and Fe/S-rich particles. Highly labile source of Fe in corn BP could be originated from amorphous Fe form mixed internally with K-rich particles. However, Fe in coal FA was dominated by the more insoluble forms of both Fe-bearing aluminosilicate glass and Fe oxides. The data presented herein showed that iron speciation varies by source and is an important factor controlling iron solubility from these anthropogenic emissions in acidic solutions, suggesting that the variability of iron solubility from combustion-derived particles is related to the inherent character and origin of the aerosols themselves. Such information can be useful in improving our understanding on iron solubility from combustion aerosols when they undergo acidic processing during atmospheric transport.
The 367 nm photochemistry of 70 monolayer (ML) OClO films and OClO adsorbed on ice is described. Gas-phase photoproducts formed during irradiation were detected with time-of-flight quadrupole mass spectrometry (TOF-QMS). For the OClO thin films, the major gas-phase photoproducts are OClO, OCl, and O 2 . The OClO and OCl TOF spectra could be fit to Maxwell-Boltzmann distributions, with temperatures of 967 ( 110 and 1721 ( 173 K, respectively. The O 2 TOF spectrum has fast and slow components that are fit to two Maxwell-Boltzmann distributions with temperatures of 70 ( 7 and 1165 ( 171 K. Photoproducts retained in the film or on the ice surface were characterized by reflection absorption infrared spectroscopy (RAIRS) and temperature-programmed desorption (TPD). The predominant photoproducts retained in the films were identified as larger Cl x O y compounds, including ClClO 2 , Cl 2 O 3 , and Cl 2 O 4 . For OClO adsorbed on ice at coverages between 0.5 and 2 ML, photoexcitation at 367 nm results only in ClClO 2 formation without formation of other photoproducts of formula Cl x O y . The formation of ClClO 2 is consistent with irradiation of OClO aggregates on the ice surface.
The 248 nm photochemistry of methyl iodide thin films was studied using reflection absorption infrared spectroscopy (RAIRS), temperature programmed desorption (TF'D), and time-of-flight quadrupole mass spectrometry (TOF-QMS). The formation of predominantly CH212 and C h and some C2H6, CH3CH21, CHI3, and I2 photoproducts retained in the film was characterized by RAIRS and TPD. The integrated areas of the IR absorption bands for the two major photoproducts, CH212 and C h , increase to a maximum and then decrease as photolysis of the film proceeds. A cross section for the loss of CH31 by 248 nm photolysis of the film was measured to be (1.6 f 0.1) x cm2, approximately 1 order of magnitude lower than the gasphase cross section. At all laser fluences used in this study, CH3, I, and CH31 were ejected into the gas phase. The CH3 TOF distribution showed the signature of gas-phase CH31 photodissociation dynamics-two sharp peaks corresponding to the production of iodine atoms in the I(2P3/2) and I*(2P112) states. The TOF distributions of I and CH31 were fit by Maxwell-Boltzmann distributions corresponding to temperatures of 1400 and 1170 K, respectively. Three other species-Ch, I2 and CH&-were observed in TOF-QMS, but only at higher laser fluences. It was determined that the I2 and CH212 species are most likely fragments of a larger molecule, perhaps a cluster species, that photodesorbs as the film becomes enriched with photoproducts.The mechanism for C h photoejection appears to be of a different nature. The photochemistry of methyl iodide thin films can be understood in terms of a combination of photoprocesses occurring in the film and at the film surface.
Electron energy loss spectroscopy is used to record the vibrational spectra of CF, (3c = 2 and 3) groups adsorbed on Pt(ll1). CF3 groups are produced from either the thermal decomposition of adsorbed CF31 or broadband photolysis of adsorbed CF3Br. The angular profile of the loss peak intensities indicates that adsorbed CF3 groups retain the gas-phase C3" symmetry. CF3 is stable on the surface until T -450 K heating to higher temperatures results in the decomposition of CF3 to yield adsorbed CF2. (36)CRC, Handbook of Chemistry and Physics, 72nd ed.; CRC Press: Boca Raton, FL, 1991. (43) Zaera, F.; Hoffian, H.
We have investigated the photodissociation of chlorobenzene and 3-chloropyridine adsorbed on smooth and rough Ag surfaces. Photolysis of adsorbed chlorobenzene and 3-chloropyridine with UV radiation results in C-Cl bond dissociation. Biphenyl and bipyridyl desorb from the surface near 400 K, and AgCl desorbs near 800 K in postirradiation temperature-programmed desorption. Compared to a smooth surface, there is a red shift in the photodissociation threshold for both molecules when adsorbed on a rough surface. Possiblemechanisms for the red shift are discussed. This study demonstrates the importance of substrate morphology on surface photochemistry.
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