The interactions of the iron monocation with water molecules and argon atoms in the gas phase were studied computationally to elucidate recent infrared vibrational spectroscopy on this system. These calculations employ first-principles all-electron methods performed with B3LYP/DZVP density functional theory. The ground state of Fe(+)(H(2)O) is found to be a quartet (M = 2S + 1 = 4, S is the total spin). Different binding sites for the addition of one or two argon atoms produce several low-lying states of different geometry and multiplicity in a relatively small energy range for Fe(+)(H(2)O)-Ar(2) and Fe(+)(H(2)O)(2)-Ar. In both species, quartet states are lowest in energy, and sextets and doublets lie at higher energies from the respective ground states. These results are consistent with the conclusion that the experimentally determined infrared photodissociation spectra (IRPD) of Fe(+)(H(2)O)-Ar(2) and Fe(+)(H(2)O)(2)-Ar are complicated because of the presence of multiple isomeric structures. The estimated IR bands for the symmetric and asymmetric O-H stretches from different isomers provide new insight into the observed IRPD spectra.

In this study, atmospheric mercury concentration in airborne particulate matter with an aerodynamic diameter ≤ 2.5 µm (PM) was analyzed by ICP-MS. Samples were collected in the Mexico City Metropolitan Area (MCMA), during 2013, in five locations, Northwest, Northeast (NE), Central, Southwest and Southeast, along three seasons: dry warm, rainy, and dry cold (DC). It can be observed that NE shows the highest mercury concentration (p < 0.05), where pollution events were identified. The seasonal distribution shows that samples collected during DC present the highest concentration (p < 0.05). These results are in agreement with the distribution of important mercury industrial sources located in the northern urban area as well with the temperature and wind conditions during 2013. The comparison of data obtained in this work with those of similar previous studies clearly indicates a decrease, between 2006 and 2013, of mercury content in PM collected in MCMA.

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The study of airborne metals in urban areas is relevant due to their toxic effects on human health and organisms. In this study, we analyzed metals including rare earth elements (REE) in particles smaller than 2.5 μm (PM), collected at five sites around the Mexico City Metropolitan Area (MCMA), during three periods in 2011: April (dry-warm season, DW), August (rainy season, R), and November (dry-cold season, DC). Principal component analysis allowed identifying factors related to geogenic sources and factors related to anthropogenic sources. The recognition of the high impact of geogenic sources in PM is in agreement with the REE distribution patterns, which show similar behavior as those shown by igneous rocks, confirming the influence of the regional geogenic material. Metals associated to geogenic sources showed higher concentration (p < 0.05) at NE of the MCMA and a significant correlation with prevalent winds. Geogenic metals show similar seasonal distribution, with the highest concentration during DW (p < 0.05), suggesting a possible metal resuspension effect which affects more significantly at lower relative humidity (RH). The metals associated with anthropogenic sources are in agreement with the urban complexity of the area, showing homogenous distribution throughout MCMA (p > 0.05) and no similar seasonal pattern among them. These unexpected results exposed outstanding information regarding the identification of different geogenic sources as the main contributors of metals in the atmospheric environment in the MCMA and highlighted the importance of meteorology in the spatial and seasonal metal patterns.

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