During the last 10 years, high atmospheric concentrations of airborne particles recorded in the Mexico City metropolitan area have caused concern because of their potential harmful effects on human health. Four monitoring campaigns have been carried out in the Mexico City metropolitan area during 2000 -2002 at three sites: (1) Xalostoc, located in an industrial region; (2) La Merced, located in a commercial area; and (3) Pedregal, located in a residential area. Results of gravimetric and chemical analyses of 330 samples of particulate matter (PM) with an aerodynamic diameter less than 2.5 m (PM 2.5 ) and PM with an aerodynamic diameter less than 10 m (PM 10 ) indicate that (1) PM 2.5 /PM 10 average ratios were 0.42, 0.46, and 0.52 for Xalostoc, La Merced, and Pedregal, respectively; (2) the highest PM 2.5 and PM 10 concentrations were found at the industrial site; (3) PM 2.5 and PM 10 concentrations were lower at nighttime; (4) PM 2.5 and PM 10 spatial averages concentrations were 35 and 76 g/m 3 , respectively; and (5) when the PM 2.5 standard was exceeded, nitrate, sulfate, ammonium, organic carbon, and elemental carbon concentrations were high. Twenty-four hour averaged PM 2.5 concentrations in Mexico City and

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This paper presents the results of the first reported study on fine particulate matter (PM) chemical composition at Salamanca, a highly industrialized urban area of Central Mexico. Samples were collected at six sites within the urban area during February and March 2003. Several trace elements, organic carbon (OC), elemental carbon (EC), and six ions were analyzed to characterize aerosols. Average concentrations of PM with aerodynamic diameter of less than 10 m (PM 10 ) and fine PM with aerodynamic diameter of less than 2.5 m (PM 2.5 ) ranged from 32.2 to 76.6 g m Ϫ3 and 11.1 to 23.7 g m Ϫ3, respectively. OC (34%), SO 4 ϭ (25.1%), EC (12.9%), and geological material (12.5%) were the major components of PM 2.5 . For PM 10 , geological material (57.9%), OC (17.3%), and SO 4 ϭ (9.7%) were the major components. Coarse fraction (PM 10 Ϫ PM 2.5 ), geological material (81.7%), and OC (8.6%) were the dominant species, which amounted to 90.4%. Correlation analysis showed that sulfate in PM 2.5 was present as ammonium sulfate. Sulfate showed a significant spatial variation with higher concentrations to the north resulting from predominantly southwesterly winds above the surface layer and by major SO 2 sources that include a power plant and refinery. At the urban site of Cruz Roja it was observed that PM 2.5 mass concentrations were similar to the submicron fraction concentrations. Furthermore, the correlation between EC in PM 2.5 and EC measured from an aethalometer was r 2 ϭ 0.710. Temporal variations of SO 2 and nitrogen oxide were observed during a day when the maximum concentration of PM 2.5 was measured, which was associated with emissions from the nearby refinery and power plant. From cascade impactor measurements, the three measured modes of airborne particles corresponded with diameters of 0.32, 1.8, and 5.6 m.

Modeling and hydraulic characterization of a filter-press-type electrochemical reactor was studied by means of residence time distribution and hydraulic indices. For these purposes, a theoretical and approximation of residence time distribution experimental curves with axial dispersion model and Danckwerts’ boundary conditions, the Morrill dispersion index, the short-circuiting index, the Morrill volumetric efficiency index, and useful volume percent were used in order to establish deviation from plug-flow ideal, as well as dead volume, and the hydraulic efficiency. The hydraulic efficiency measure of the filter-press-type electrochemical reactor confirms uniformity of flow and a highly effective useful volume percent (91 %-98 % for all liquid flow rates tested). The axial dispersion coefficients computed (0.0005–0.0021 m2/s) indicates a small deviation of plug-flow ideal. Hence, the plug-flow reactor model is reliable for purpose modeling of the filter-press-type electrochemical reactor used in this research. Furthermore, hydrodynamic characterization of the tested filter-press-type electrochemical reactor by using hydraulic indices demonstrated its suitability for several electrochemical applications.

The application of Response Surface Methodology (RSM) and Central Composite Rotatable Design (CCRD) for modeling and optimization of the influence of three operating variables (mass of catalyst, MeOH/Oil molar ratio, and temperature) on performance of Reactive Vacuum Distillation (RVD) to increase biodiesel yield is discussed in this work. Changes in RVD performance during biodiesel production were evaluated by using RSM and CCRD. A mathematical equation to model biodiesel production by RVD was derived from computer simulation programming by applying a least squares method using MATLAB® v. R2016a. Predicted values were found to be in good agreement with experimental values (with R2 = 0.934). Optimal conditions for the production of ethyl esters were: Temperature: 31.2 °C, MeOH/Oil molar ratio: 5.65:1, and mass of catalyst: 0.1344 g.