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We measured and compared mercury (Hg) and other ions in rainwater collected in San Joaquin (mining zone) and Juriquilla (urban area), central Mexico, from 2009 to 2012. A total of 274 rainwater samples were collected and analyzed for pH, electrical conductivity, NO3-,SO42-, Cl−, NH4+, Na+, K+, Ca2+, Mg2+ and Hg. Mercury concentrations in rainwater varied from 24.21 to 248.89 (x-bar = 86.97 ± 10.77) µg L− 1 in San Joaquin (mining zone) and 11.26 to 176.91 (x-bar = 81.51 ± 10.24) µg L− 1 in Juriquilla (urban area). Rainwater sample were collected over periods 1-3 days, depending upon precipitation frequency. Significant correlations (p < 0.05) were found between SO42-, Cl−, NO3-, Na+, K+, Ca2+, Mg2+ and Hg at the San Joaquin site. Significant correlations were obtained between SO42-,NO3-,NH4+, Na+, K+, Ca2+, Mg2+ and Hg at the Juriquilla site. In order to determine if there were significant differences among each measured parameter in rainwater collected in San Joaquin and Juriquilla, Kruskal-Wallis test was applied to data. We emphasized that the distribution and concentrations of Hg and the studied ions in rainwater samples were affected by atmospheric dust and local meteorological conditions of wind-speed and direction. [ABSTRACT FROM AUTHOR]

Atmospheric aerosol particles were collected from January to December 2007 at two sites in the City of Guadalajara. The first site (Centro) is located in the downtown, which is characterized by high vehicular traffic, and the second site (Miravalle) is in the southern part of the city, characterized by emissions from high industrial and vehicular activity. Sulfates, nitrates, and ammonium were the most abundant ions at both sites. Similar concentrations of sulfates, nitrates, and ammonium were observed throughout the year at Centro while only sulfates and nitrates were similar at Miravalle. From the balance of anions and cations at the two sites, Centro was determined to have acidic particles, while at Miravalle, the particles were alkaline. Based on the analysis of the ammonium/sulfate molar ratios, it was determined that in Centro, there was not enough ammonium to neutralize the sulfate, while at Miravalle, ammonium practically neutralized all sulfate. [ABSTRACT FROM AUTHOR]

Abstract: Inorganic ions and trace metals in total suspended particles were measured during the period 2006–2007 at four sites; three urban sites in the Mexico City Metropolitan Area (MCMA) and one nearby rural site in the state of Morelos. SO4 2−, NO3 −, Cl− and NH4 + ions were analyzed by ion chromatography; Na+, K+, Ca2+ and Mg2+ by flame atomic absorption spectroscopy, and Al, Cd, Cr, Mn, Pb and V by an atomic absorption spectrometer with a graphite furnace attachment. The results indicated that SO4 2− was the most abundant ion. All trace elements except Mn and V showed statistically significant differences between sampling sites. Pearson''s correlation applied to all data showed a high correlation among SO4 2−, NO3 − and NH4 +, indicating a common anthropogenic origin. In addition, the correlation observed between Ca2+ and Al indicated a crustal origin, as supported by the enrichment factors. Over the total sampling period, significant differences in particles and trace metals were found between sites and meteorological seasons. To gain a better insight into the origin of trace metals and major inorganic ions, a Principal Component Analysis was applied to the results for six trace metal and eight inorganic ions. [Copyright &y& Elsevier]

Size-differentiated atmospheric aerosol particles were collected during December 2000–October 2001 in Mexico City (19°N, 99°W) using a micro-orifice uniform deposit impactor. Sulfate and ammonium, which were correlated, were major features of the size distributions. The more predominant mode was at 0.32±0.1 μm, aerodynamic diameter. This peak of concentration is likely the result of condensation of secondary aerosol components from the gas phase. During part of the rainy season (April and June), a larger mode was found at 0.56±0.2 μm, aerodynamic diameter. This peak of concentration, identified as a droplet mode, is probably the result of aqueous-phase reactions (i.e., oxidation of sulfur dioxide in liquid droplets). During August, the peak of concentration was observed at both size ranges of the accumulation mode. Overall, ion balances were achieved with a small deficit of cations, except for the April and June samples, where a significant amount of excess sulfate was present as a result of moderate–high activity of the neighboring volcano Popocatepetl, as well as ambient conditions that favored production of sulfate (moderate–high relative humidity values). Based on the analysis of the ammonia/sulfate molar ratios, the ammonia concentrations were sufficient to fully neutralize sulfate concentrations, except for the April and June samples. During these months, ammonium bisulfate, letovicite and H2SO4(aq) (or a solution of the corresponding ions) were the dominant form of sulfate present in both fine and coarse modes. The acidic nature of these particles (with NH3/H2SO4 molar ratio less than 2) is potentially important in assessing health effects of inhaled particles. [Copyright &y& Elsevier]