Alejandro Salcido

Study of the regional air quality south of Mexico City (Morelos state)

Results from the first study of the regional air quality in Morelos state (located south of Mexico City) are presented. Criteria pollutants concentrations were measured at several sites within Morelos in February and March of 2007 and 2009; meteorological data was also collected along the state for the same time periods; additionally, a coupled meteorology-chemistry model (Mesoscale Climate Chemistry Model, MCCM) was used to gain understanding on the atmospheric processes occurring in the region. In general, concentrations of almost all the monitored pollutants (O(3), NO(x), CO, SO(2), PM) remained below the Mexican air quality standards during the campaign; however, relatively high concentrations of ozone (8-hour average concentrations above the 60 ppb level several times during the campaigns, i.e. exceeding the World Health Organization and the European Union maximum levels) were observed even at sites with very low reported local emissions. In fact, there is evidence that a large percentage of Morelos vegetation was probably exposed to unhealthy ozone levels (estimated AOT40 levels above the 3 ppm h critical limit). The MCCM qualitatively reproduced ozone daily variations in the sites with an urban component; though it consistently overestimated the ozone concentration in all the sites in Morelos. This is probably because the lack of an updated and detailed emission inventory for the state. The main wind patterns in the region corresponded to the mountain-valley system (downslope flows at night and during the first hours of the day, and upslope flows in the afternoon). At times, Morelos was affected by emissions from surrounding states (Distrito Federal or Puebla). The results are indicative of an efficient transport of ozone and its precursors at a regional level. They also suggest that the state is divided in two atmospheric basins by the Sierras de Tepoztlán, Texcal and Monte Negro.

Least squares variational approach to the convective mixing height estimation problem

Abstract A least squares variational approach is suggested to estimate the atmospheric mixed layer depth (or mixing height ) under convective conditions from the vertical profile of virtual potential temperature. This method was implemented as a software application that could be a very useful tool to estimate the mixing height parameter required in air pollution modeling studies. The software was used to estimate Mexico City mixing heights from the atmospheric sounding data between January to May of 1993 and 1994, and the monthly statistics evolution of the 11:00z and 23:00z mixing height values is presented for this period. The estimations produced by this method for the afternoon mixing height were found in a good agreement with the daily maximum value calculated with the dry adiabatic temperature method.

Daytime net radiation parameterisation for Mexico City suburban areas

This study presents a simple parameterisation for forecasting daytime net radiation in a Mexico City suburban area (Texcoco). The main characteristic of the parameterisation is that the only input data are the global solar radiation and air temperature trends. Reliability of the model was verified by measurements performed during two experimental campaigns carried out in 1992 and 1993 under a contract sponsored by the European Community. The forecast and the experimental data were found to agree very well even in disturbed meteorological situations.

Main Characteristics of Mexico City Local Wind Events during the MILAGRO 2006 Campaign within a Meso-β Scale Lattice Wind Modeling Approach

A characterization of local wind events in Mexico City, which occurred during MILAGRO campaign, was carried out within the framework of a lattice wind modeling approach at a meso-β scale. Mexico City was modeled as a 2D lattice domain with a given number of identical cells. Local wind conditions at any cell were described by a state variable defined by the spatial averages of wind attributes such as speed, direction, divergence, and vorticity. Full and partial densities of wind states were discussed under different conditions using two simple lattice wind models. We focus on the results obtained with the 1-cell lattice wind model and provide brief comments about preliminary results obtained with the 4-cell model. The 1-cell model allowed identifying the main patterns of the wind circulation in Mexico City throughout the study period (anabatic and katabatic winds, winds induced by the urban heat island, and winds with high possibilities for exchanging pollutants between Mexico City and the neighboring settlements, among others). The model showed that Mexico City wind divergence and vorticity disclose superposed oscillations whose most important periods were 24 and 12 hours, suggesting strong connections with the diurnal cycle of incoming solar radiation and the urban heat island.

Equilibrium Properties of the Cellular Automata Models for Traffic Flow in a Single Lane

In the last thirty years, the application of cellular automata as models of physical systems has attracted much attention, particularly for studying and simulating behaviour of fluid systems and traffic flow. In this work we present a theoretical analysis of the equilibrium properties of the cellular automata models for multi-speed traffic flow in a single lane highway. We hope our studies may advance some steps in the line of establishing a quite well formulated physical theory for these models. Our interest in this problem comes from the believe that general theoretical results about the traffic cellular automata may help very much to improve the speed of the associated computer models that scientists and engineers use for traffic flow simulations; but on another hand, it is much close related to the need of having, in a near future, a simple, but efficient tool for estimating the distribution in space and time of the pollutant emission rates coming from vehicular traffic in urban settlements, in such a way we can use the simulation results as the emissions input for the air pollution dispersion models we use to asses air quality in big urban places like Mexico city.

A THEORETICAL-ANALYSIS OF PHONON-SPECTRA IN HIGH-TC SUPERCONDUCTORS

Abstract The normal modes of vibration of the superconductors Y 1 Ba 2 Cu 3 O 7 and related compounds are calculated using the harmonic aproximation. The conditions for the Jahn-Teller effect and its influence on the phonon density of states are analysed.

A Brief Clustering Analysis of the Mexico City Local Wind States Occurred during the Milagro Campaign

A clustering analysis of the Mexico City local wind events that occurred during the MILAGRO field campaign was carried out for identifying their main characteristics and patterns. This study was performed with the hourly wind data provided by the official atmospheric monitoring network for March 2006. The local winds of the period were described with a meso-β scale lattice wind model endowed with a wind state concept defined by the wind velocity horizontal components and the wind’s divergence and vorticity. The wind states produced by the lattice wind model were analyzed through their occurrence frequencies and hierarchical cluster analysis. This procedure revealed wind patterns very similar to those already described by other authors. However, new and interesting features were also revealed such as a strongly stable cluster composed by wind states befallen from sunrise to midafternoon, and that the 4-group clustering revealed itself as the more stable wind states organization, while those with 6 and 8 clusters resulted the less stable ones. A Fourier transform analysis of the wind states time series evidenced wind patterns driven by the diurnal cycle of incoming solar radiation, and other patterns that may be associated with the urban heat island phenomenon.

A theoretical phonon calculation in the Bi2Sr2CaCu2O8 superconductor

Abstract The normal modes of vibration of the Bi 2 Sr 2 CaCu 2 O 8 superconducting material (with Tc near 85 K) are calculated within the harmonic approximation. The theoretical group analysis of the normal modes and the phonon density of states are reported.

Jahn-Teller effect in the LaSrCuO superconductor

The CuO 6 octahedron in the T structure of the La-Sr-Cu-O superconductor is considered within the quasi-molecular approximation in order to calculate the electronic structure and the vibrational modes that could participate in the Jahn-Teller effect. The electronic calculations are made within the extended Huckel model and the vibrations are taken from previously reported results. Once the electronic and vibrational participants are determined using group theory analysis, the intensity of the electron-phonon interaction is calculated to establish the Jahn-Teller deformation

High frequency vibrations in the YBaCuO superconductor

Abstract We perform a theoretical calculation of the effective temperature T eff for the high T c superconductor YBa 2 Cu 3 O 7 as a function of the force constants in a lattice dynamic model. From the partial phonon density of states it is shown how Cu atoms might have higher frequency vibrations than O atoms and therefore higher T eff .