Mexico City Metropolitan Zone Research Articles

Spatial and temporal variation of acid rain in the Mexico City Metropolitan Zone

At the end of the 1980´s particulates and sulfur dioxide (SO 2 ) were the main atmospheric pollutants in the Mexico City Metropolitan Zone (MCMZ). To reduce emissions, fuel oil was replaced by natural gas at power plants located inside Mexico City. Currently, SO 2 levels do not exceed its air quality standard; however, acid rain is present with a high contribution of sulfate (SO 4 2– ). In this study, spatial and temporal variations in the chemical composition of rain in Mexico City between 2003 and 2014 were analyzed. Major ions (Na + , NH 4 +, K + , Mg 2+ , Ca 2+ , SO 4 2– , NO 3 – and Cl – ), pH, and electrical conductivity (EC) were analyzed weekly at 16 sampling stations located in the MCMZ. The pH decreased from north to south, with the lowest annual volume weighted mean (VWM) of 4.16 in 2006. Annual ion concentrations were, in decreasing order: NH 4 + , SO 4 2 – , NO 3 – and Ca 2+ for the entire study period at most of the sampling sites. The highest values for wet atmospheric deposition (kg/ha) were found in the Western area and were the maximum in 2007. Wet deposition had major levels for SO 4 2– and NO 3 – of 24 and 20 kg/ha, respectively, and were similar to the levels registered in the USA in 2013 and 2014. Considering that external emission sources play a decisive role in acid rain within the City, it is necessary to establish strategies for the emission reductions of acid rain precursors from upwind sources.

Impacts of Stabilized Criegee Intermediates, surface uptake processes and higher aromatic secondary organic aerosol yields on predicted PM2.5 concentrations in the Mexico City Metropolitan Zone

The Community Multiscale Air Quality Model (CMAQ) with the SAPRC-99 gas phase photochemical mechanism and the AERO5 aerosol module was applied to model gases and particulate matter (PM) concentrations in the Mexico City Metropolitan Zone (MCMZ) and the surrounding regions for March 2006 using the official 2006 emission inventories, along with emissions from biogenic sources, biomass burning, windblown dust, the Tula Industrial Complex and the Popocatépetl volcano. The base case model was capable of reproducing the observed hourly concentrations of O3 and attaining CO, NO2 and NOx performance similar to previous modeling studies. Although the base case model performance of hourly PM2.5 and PM10 meets the model performance criteria, under-prediction of high PM2.5 concentrations in late morning indicates that secondary PM, such as sulfate and secondary organic aerosol (SOA), might be under-predicted. Several potential pathways to increase SOA and secondary sulfate were investigated, including Stabilized Criegee Intermediates (SCIs) from ozonolysis reactions of unsaturated hydrocarbons and their reactions with SO2, the reactive uptake processes of SO2, glyoxal and methylglyoxal on particle surface and higher SOA formation due to higher mass yields of aromatic SOA precursors. Averaging over the entire episode, the glyoxal and methylglyoxal reactive uptake and higher aromatics SOA yields contribute to ∼0.9 μg m−3 and ∼1.25 μg m−3 of SOA, respectively. Episode average SOA in the MCMZ reaches ∼3 μg m−3. The SCI pathway increases PM2.5 sulfate by 0.2–0.4 μg m−3 or approximately 10–15%. The relative amount of sulfate increase due to SCI agrees with previous studies in summer eastern US. Surface SO2 uptake significantly increases sulfate concentration in MCMZ by 1–3 μg m−3 or approximately 50–60%. The higher SOA and sulfate leads to improved PM2.5 and PM10 model performance.

Temporal disaggregation and restricted forecasting of multiple population time series

This article presents some applications of time-series procedures to solve two typical problems that arise when analyzing demographic information in developing countries: (1) unavailability of annual time series of population growth rates (PGRs) and their corresponding population time series and (2) inappropriately defined population growth goals in official population programs. These problems are considered as situations that require combining information of population time series. Firstly, we suggest the use of temporal disaggregation techniques to combine census data with vital statistics information in order to estimate annual PGRs. Secondly, we apply multiple restricted forecasting to combine the official targets on future PGRs with the disaggregated series. Then, we propose a mechanism to evaluate the compatibility of the demographic goals with the annual data. We apply the aforementioned procedures to data of the Mexico City Metropolitan Zone divided by concentric rings and conclude that the targets established in the official program are not feasible. Hence, we derive future PGRs that are both in line with the official targets and with the historical demographic behavior. We conclude that growth population programs should be based on this kind of analysis to be supported empirically. So, through specialized multivariate time-series techniques, we propose to obtain first an optimal estimate of a disaggregate vector of population time series and then, produce restricted forecasts in agreement with some data-based population policies here derived.

Nuevos patrones espaciales en las derramas de empleo en la zona metropolitana de la Ciudad de México

<p>En la Zona Metropolitana de la Ciudad de México (ZMCM) la generación de derramas en el empleo puede estar asociada, entre otros factores, a la adopción de nuevas tecnologías (vía inversión extranjera directa), a la inmigración de gente calificada o talentosa, y/o a la presencia de centros de investigación y desarrollo. En este trabajo se analiza el papel de las derramas en el empleo del sector manufacturero y en el sector de servicios profesionales a través de dos grupos que hemos clasificado como creativos y tecnológicos. El resultado central de este trabajo es que los patrones de derrama de empleo se han modificado durante las últimas dos décadas y han estado condicionados por la intensificación del proceso de terciarización que ha experimentado la ZMCM. En particular se propone que este proceso de reconversión económica de la metrópoli ha generado que los efectos derrama de empleo operen en distancias cortas de difusión espacial.</p>

La ciudad central de la Ciudad de México: ¿espacio de oportunidad laboral para la metrópoli? / Mexico City’s Downtown Area: a Job Opportunity Area for the Metropolis?

Las áreas centrales de las grandes metrópolis han perdido población y transformado sus actividades económicas como respuesta a la redistribución intrametropolitana de la población y los cambios en la demanda ocupacional. ¿Significa que los centros de las ciudades han perdido su centralidad? El concepto de centralidad puede ser abordado desde diferentes perspectivas, pero todas ellas enfatizan la concentración espacial de funciones urbanas y actividades económicas. En este documento se analiza la evolución de la demanda ocupacional en la Zona Metropolitana de la Ciudad de México entre 1980 y 2003, y en particular en su ciudad central. El periodo de estu­dio se inscribe en un contexto nacional y local de reestructuración económica, e interesa conocer el papel de la ciudad central en el crecimiento económico y en la generación de empleo metropolitano, así como en su transformación económica y ocupacional.AbstractDowntown areas of large metropolises have seen a decline in population and transformed their economic activities as a response to intra-metropolitan population redistribution and changes in occupational demand. Does this mean that city centers have lost their centrality? Although the concept of centrality can be dealt with from various perspectives, they all emphasize the spatial concentration of urban functions and economic activities. This document analyzes the evolution of occupational demand in the Mexico City Metropolitan Zone between 1980 and 2003, particularly in its downtown area. The period of study is framed within a national and local context of economic restructuring and focuses on the role of Mexico city’s downtown area in economic growth and the creation of metropolitan employment, as well as its economic and occupational transformation

La situación actual del sistema de monitoreo ambiental en la Zona Metropolitana de la Ciudad de México / The Current Status of Environmental Monitoring in the Mexico City Metropolitan Zone

Se ha visto que sin un sistema de monitoreo ambiental integral y eficiente, que propor­cione datos duros de soporte para un diagnóstico de la situación ambiental, no es posible elaborar nuevas políticas públicas para resolver la problemática que enfrentan las áreas urbanas. En el presente trabajo se revisa la situación actual del sistema de monitoreo ambiental de la Zona Metropolitana de la Ciudad de México desde tres ángulos: climatológico, hidrométrico y de calidad de aire. Asimismo se detectan sus principales avances, limitaciones y otras particularidades y al final se complementa el monitoreo ambiental con la parte social y económica. AbstractIt has been proved that without an efficient, integral environmental monitoring system that provides hard back-up data for a diagnosis of the environmental situation, it is impossible to draw up new public policies to solve the problem faced by urban areas. This paper reviews the current status of environmental monitoring in the Mexico City Metropolitan Zone from three angles: climatological, hydrometric and air quality. It also detects the main progress, limitations and other particularities and at the end, environmental monitoring is complemented by the social and economic part.

Historical PCB fluxes in the Mexico City Metropolitan Zone as evidenced by a sedimentary record from the Espejo de los Lirios lake

The accumulation of PCBs over time was studied in a sediment core collected from Espejo de los Lirios, an ecological reserve located within the heart of Cuatitlan Izcalli, in the Northern part of Mexico City Metropolitan Zone. A 210Pb-derived chronology, was used to reconstruct the historical PCB fluxes to the site during ∼84 yr (1911–95). The highest input fluxes occurred in the 1977, after a significant increase after the late 1940s. This trend is clearly the consequence of the increasing emissions that are related to the onset of industrial activities starting from early 1970s. A phase of decrease, after the ban of the use in open systems, ended in 1989 and in 1995, at the time of sampling, the trend was toward a new increase to the highest levels. A reconstruction of PCB atmospheric concentration from sedimentary fluxes is attempted; and the estimate suggests that PCBs concentrations in the air of the Cuautitlán Izcalli seem not of concern. Nonetheless, the contamination levels found in the sediments are relatively high, reaching values above the threshold effect level (TEL) guidelines and, in two cases, close to the probable effect level (PEL) which mean that some adverse effects on the fauna may have occurred all over the time interval represented by the core.

Las corrientes migratorias en las ciudades contiguas a la Zona Metropolitana de la Ciudad de México: el caso de la aglomeración urbana de Pachuca / Migratory Trends in Cities Adjacent to the Mexico City Metropolitan Area. The Case of Urban Agglomeration i

En los últimos veinte años la ciudad de Pachuca ha sufrido grandes transformaciones en su territorio; el ritmo de crecimiento poblacional ha provocado que la ciudad se expanda físicamente como no lo había hecho en sus casi quinientos años de existencia. Una parte de este crecimiento poblacional se debe a los procesos inmigratorios que han ocurrido en los últimos años. Tomando en cuenta las tendencias y las experiencias de otras ciudades contiguas a la Zona Metropolitana de la Ciudad de México, pensamos que el actual flujo migratorio se consolidará e intensificará en los próximos años. De ahí que el objetivo del presente trabajo sea realizar un estudio sobre las corrientes migratorias en el espacio urbano de Pachuca, describiendo el perfil del migrante según los flujos establecidos. Nos interesa prever los cambios económicos y sociales en la ciudad, el desarrollo de su influencia regional y su nuevo papel en el sistema de ciudades y en la megalópolis de la Ciudad de México. AbstractOver the past twenty years, the city of Pachuca has undergone enormous transformations in its territory while the rate of population growth has meant that the city has expanded more than ever before in its nearly 500 years of existence. Part of this population growth is due to the migratory processes that have taken place in recent years. Given the trends and experiences of other cities adjacent to the Mexico City Metropolitan Zone, the authors believe that the current migratory flow will be consolidated and intensified over the next few years. The aim of this study is to therefore to undertake a study of migratory trends in the urban space of Pachuca, by describing migrants’ profiles according to the established flows. The authors are interested in predicting the economic and social changes in the city, the development of its regional influence and its new role in the system of cities and the Mexico City megalopolis.

The Basin of Mexico aquifer system: regional groundwater level dynamics and database development

The aquifer system of the Basin of Mexico is the main source of water supply to the Mexico City Metropolitan Zone. Management of the Basin’s water resources requires improved understanding of regional groundwater flow patterns, for which large amounts of data are required. The current study analyses the regional dynamics of the potentiometric groundwater level using a new database called the Basin of Mexico Hydrogeological Database (BMHDB). To foster the development of a regional view of the aquifer system, data on climatological, borehole and runoff variables are part of the BMHDB. The structure and development of the BMHDB are briefly explained and then the database is used to analyze the consequences of groundwater extraction on the aquifer’s confinement conditions using lithology data. The regional analysis shows that the largest drawdown rates are located north of Mexico City, in Ecatepec (a region that has not yet received attention in hydrogeological studies), due to wells that were drilled as a temporary solution to Mexico City’s water-supply problem. It is evident that the aquifer has changed from a confined to an unconfined condition in some areas, a factor that is responsible for the large subsidence rates (40 cm/year) in some regions.

La expansión urbana probable de la Ciudad de México. Un escenario pesimista y dos alternativos para el año 2020 / Mexico City’s Probable Urban Expansion. A Pessimistic Scenario and Two Alternatives for the Year 2020

De acuerdo con las proyecciones del Consejo Nacional de Población (Conapo), la Zona Metropolitana de la Ciudad de México (zmcm) albergará una población de más de 21 millones de habitantes para 2020. Suponiendo que estas estimaciones fueran correctas, es importante prever en dónde se llevará a cabo este crecimiento y cómo afectará la estructura urbana. En este ensayo se analizan tres escenarios de expansión metropolitana elaborados conforme a diferentes supuestos de densidad poblacional y estimados mediante un análisis estadístico espacial por medio del Sistema de Información Geográfica (SIG). Los resultados revelan una expansión de la superficie urbana para el año 2020, según el escenario, de entre 38 mil y 56 mil hectáreas. Se concluye que se requieren de modelos de administración pública metropolitana conjunta para controlar la forma de expansión y para regular los usos de suelo de la ZMCM. AbstractAccording to the forecasts of the National Population Council (Conapo), by 2020, the Mexico City Metropolitan Zone (MCMZ) will house a population of over 21 million in­habitants. Assuming that these estimates are correct, it is important to predict where this growth will take place and how it will affect the urban structure. This essay analyzes three scenarios of metropolitan expansion drawn up on the basis of different assumptions of population density and estimates through a spatial statistical analysis using the Geographical Information System. The results reveal an expansion of the urban area by the year 2020, according to the scenario, of between 38,000 and 56,000 hectares. The authors conclude that models of joint metropolitan public administration are required to control the form of expansion and regulate mcmz land uses.

12 Comprehensive geriatric assessment (CGA) in elderly women with early breast cancer

The accumulation of PCBs over time was studied in a sediment core collected from Espejo de los Lirios, an ecological reserve located within the heart of Cuatitlan Izcalli, in the Northern part of Mexico City Metropolitan Zone. A 210Pb-derived chronology, was used to reconstruct the historical PCB fluxes to the site during ∼84 yr (1911–95). The highest input fluxes occurred in the 1977, after a significant increase after the late 1940s. This trend is clearly the consequence of the increasing emissions that are related to the onset of industrial activities starting from early 1970s. A phase of decrease, after the ban of the use in open systems, ended in 1989 and in 1995, at the time of sampling, the trend was toward a new increase to the highest levels. A reconstruction of PCB atmospheric concentration from sedimentary fluxes is attempted; and the estimate suggests that PCBs concentrations in the air of the Cuautitlán Izcalli seem not of concern. Nonetheless, the contamination levels found in the sediments are relatively high, reaching values above the threshold effect level (TEL) guidelines and, in two cases, close to the probable effect level (PEL) which mean that some adverse effects on the fauna may have occurred all over the time interval represented by the core.

Servicios generales de la producción en la Ciudad de México / General Production Services in Mexico City

El propósito de este artículo es analizar la evolución de la concentración de los servicios públicos en la Zona Metropolitana de la Ciudad de México (ZMCM) según dos etapas: i) entre 1960 y 1982, periodo de activa participación gubernamental; y, ii) de 1980 a 1998, de adelgazamiento gubernamental e implantación del neoliberalismo.Las conclusiones de corte estructural del análisis realizado son tres: i) la creciente concentración de los servicios públicos en la ZMCM entre 1960 y 1982 refuerza la tendencia hacia su especialización terciaria; ii) la concentración en la urbe de trabajadores en actividades de los servicios generales de la producción (sgp) se reduce ligeramente de 1993 a 1998; iii) existe una concentración en la Ciudad de México semejante en los sgp que en las actividades de comercio y servicios de tipo mercantil. AbstractThis article seeks to analyze two stages in the evolution of the concentration of public services in the Mexico City Metropolitan Zone (MCMZ): i) from 1960 to 1982, the period of active government participation and ii) from 1980 to 1998, an era of government reduction and the implementation of neo-liberalism.The article provides three structural conclusions of the analysis undertaken: i) the growing concentration of public services in the MCMZ between 1960 and 1982 reinforce the trend towards its tertiary specialization; ii) the concentration of workers in the city in activities involving general production services (GPS) fell slightly between 1993 and 1998 and iii) there is a similar concentration of GPS in Mexico City to that of commercial and mercantile services.

210Pb geochronology of sediment accumulation rates in Mexico City Metropolitan Zone as recorded at Espejo de los Lirios lake sediments

A sedimentary sequence from the Espejo de los Lirios lake in the Metropolitan Zone of Mexico City (MZMC) was analyzed in detail for 210Pb and 137Cs activities, allowing to assess the evolution of the accretion rates in the lake during the last ∼84±4 years. The core revealed the deposition of contemporaneously indigenous lake sediments to the site interspersed with eroded bedrock from the catchment, evidencing episodic increases in sediment accretion which varied from 0.14 to 0.93 cm year −1. Increasing trends in sedimentation rates were found to be closely related to demographic expansion of the Metropolitan Zone of Mexico City and explained on the basis of the erosive processes produced as a result of deforestation created as a consequence of the urban and industrial development of the MZMC.

El proceso de urbanización y el crecimiento económico en México / The Process of Urbanization and Economic Growth in Mexico

El objetivo de este trabajo es analizar el impacto del proceso de urbanización en el crecimiento económico en México utilizando los métodos econométricos modernos. Los resultados obtenidos indican que existe una relación estable de largo plazo y positiva entre el producto, la inversión y un índice de urbanización. Ello indica que la inversión y el proceso de urbanización han favorecido el ritmo de crecimiento económico de México. En este sentido, el acelerado proceso de urbanización del país durante el siglo XX tuvo efectos positivos sobre el ritmo de crecimiento económico. Debe sin embargo considerarse que las características del proceso de urbanización en México se han traducido en un alto nivel de concentración económica, en particular en la Zona Metropolitana de la Ciudad de México, con costos crecientes para el crecimiento económico de largo plazo. Ello se refleja en un proceso de desconcentración de las megalópolis a zonas conurbadas en la década de los ochenta, que se ha estabilizado relativamente en los últimos años. AbstractThis article seeks to analyze the impact of urbanization on economic growth in Mexico, using modern econometric methods. The results obtained suggest that there is a stable, long-term positive relationship between the product, investment and the urbanization index. This suggests that investment and urbanization have contributed to the rate of economic growth in Mexico. In this respect, the country’s rapid urbanization in the 20th century had a positive effect on the economic growth rate. One should, however, recall that the characteristics of urbanization in Mexico have translated into a high level of economic concentration, particularly in the Mexico City Metropolitan Zone, with growing costs for long-term economic growth. This is reflected in the decentralization of megalopolises to conurbations during the 1980’s which has stabilized somewhat in recent years.

El Procede y el Piso en la incorporación del suelo de propiedad social a usos urbanos en los municipios conurbados de la ZMCM / Procede and Piso in the Incorporation of Socially-Owned Property into Urban Uses in Municipalities in the MCMZ Conurbation

En este artículo se revisan los mecanismos de incorporación regulada del suelo de origen social1 al desarrollo urbano en el ámbito de los municipios conurbados de la Zona Metropolitana de la Ciudad de México (ZMCM). A diez años de las modificaciones al artículo 27 constitucional se explora la forma en que los programas Procede y Piso han participado en la regulación del cambio de uso de suelo de rural a urbano, los factores que han influido en que los ejidatarios hayan decidido utilizar los nuevos mecanismos de desincorporación del régimen de propiedad social y la posición de los distintos actores involucrados (ejidatarios, Sector Agrario, Corett, desarrolladores privados y municipios) ante estos mecanismos. AbstractThis article reviews the mechanisms for the regulated incorporation of socially-owned property into urban development in municipalities in the Mexico City Metropolitan zone (MCMZ) conurbation. Ten years after the modifications to Article 27 of the Constitution, the author explores the role played by the implementation of the Procede and Piso programs in the regulation of the change of land use from rural to urban, the reasons why ejido owners have decided to use the new mechanisms for separating from the social property regime and the position of the various actors involved (ejido owners, Agrarian Sector, Corett, private developers and municipalities) vis-à-vis these mechanisms.

Macroeconomía del sector servicios en la Ciudad de México, 1960-1998 / Macroeconomics of the Service Sector in Mexico City, 1960-1998

En este artículo se analiza la estructura, los niveles de concentración y la dinámica del sector servicios de la Zona Metropolitana de la Ciudad de México (ZMCM) de 1960 a 1998, siguiendo las etapas de auge, crisis y recuperación relativa de la economía nacional. Se parte de la hipótesis de que la ZMCM tenderá a especializarse en los servicios al productor, pues éstos se localizan preferentemente en las grandes metrópolis, tal como acontece en las ciudades globales de los países desarrollados. Se utiliza la información de los censos económicos de comercio y servicios de 1960, 1970, 1980, 1988, 1993 y 1998, que capta datos de los negocios privados. Las estadísticas censales se sometieron a una rigurosa metodología para hacerlas comparables por grupos de actividades terciarias entre los diferentes censos, además de que se ajustaron con las cuentas nacionales. Se considera que los resultados obtenidos constituyen una nueva base de datos que refleja adecuadamente el nivel real de la concentración espacial y la dinámica de crecimiento de las actividades terciarias en México. AbstractThis article analyzes the structure, levels of concentration and dynamics of the service sector in the Mexico City Metropolitan Zone (MCMZ) from 1960 to 1998, tracing the rise, crisis and relative recovery of the national economy. The author begins with the hypothesis that the MCMZ will tend to specialize in services for producers, since the latter are usually located in metropolises, as happens in major cities in developed countries. The author uses information from the economic censuses on trade and services from 1960, 1970, 1980, 1988, 1993 and 1998, which includes data on private businesses. The statistics from these censuses were subjected to a rigorous methodology to make the groups of tertiary activities comparable within the various censuses, and were also adjusted with the National Accounts. The results obtained constitute a new data base that accurately reflects the actual level of spatial concentration and the dynamics of the growth of tertiary activities in Mexico.

Historical trace metal fluxes in the Mexico City Metropolitan Zone as evidenced by a sedimentary record from the Espejo de los Lirios lake.

The accumulation of selected trace metals (Ag, Cd, Co, Cr, Cu, Hg, Ni, Pb, V and Zn) was studied in a sediment core collected at Espejo de los Lirios lake, a precipitation-dominated seepage lake in Northern Mexico City Metropolitan Zone (MCMZ). A (210)Pb-derived chronology, obtained from the same core, was used to reconstruct the historical metal fluxes at the site, allowing evaluation of the impact of environmental changes promoted by the development of the City during the last approximately 125 years. The highest levels of metal enrichment above natural concentration levels (NCL) in the sediments from Espejo de los Lirios lake were found for Ag and Pb (approximately 250%) as well as a slight enrichment for Cd (55%), Cr (84%), Co (20%), Cu (60%), Hg (47%), Ni (45%), V (59%) and Zn (66%). Fluxes of trace metals appeared to have noticeably increased from the last 45 years showing the maximum increments for Cd, Co, Cr, Ni, V and Zn during the 1980's (9 to 13 fold natural fluxes), for Ag and Cu (17 and 12 fold, respectively) during the 1990's and for Hg and Pb (2 and 13 fold) during the middle 1970's. Low levels of metal enrichment observed have evidenced that the most conspicuous consequences of the expansive growth of this area of the MCMZ, are mostly related to deforestation and erosion of the surrounding areas, rather than to trace metal pollution. Based on PCA, it can be assumed that atmospheric deposition, weathering of bedrock and soil within the watershed and authigenic production, are the most important processes that explain the trace metal distribution in the site.

Concentrations of benzene and toluene in the atmosphere of the southwestern area at the Mexico City Metropolitan Zone

The Mexico City Metropolitan Zone (MCMZ) presents important emissions of hazardous air pollutants. It is well documented that the MCMZ suffers a critical air pollution problem due to high ozone and particulate matter concentrations. However, toxic air pollutants such as benzene and toluene have not been considered. Benzene has accumulated sufficient evidence as a human carcinogen, and the ratio benzene/toluene is an excellent indicator to evaluate control strategies efficiency. In order to evaluate the levels of these two air toxic pollutants in the MCMZ, ambient air samples were collected in canisters and analyzed with a gas chromatograph with a flame ionization detector, according to procedures described in the United States Environmental Protection Agency (USEPA) method TO-15. Quality assurance was performed collecting duplicate samples which were analyzed in replicate to quantify the precision of air-quality measurements. Three different sites located in the Southwestern area in the MCMZ were selected for the sampling: the University campus, a gas station, and a vertical condominium area, in the same neighborhood, which presents different activities. At these sites, grab air samples were collected during the morning hours (7–8 a.m.), while for the University area, 24 h integrated air samples were collected simultaneously, with grab samples. Benzene concentrations (24 h sampling) in the atmosphere around the University campus have similar present levels as in other cities of North America. Mean values in this site were about 1.7 ppb. A significant variation exists between the benzene and toluene concentrations in the studied sites, being the more critical values than those registered at the gas station (an average of 25.8 ppb and a maximum of 141 ppb of benzene). There is a fuel regulation for gasoline in Mexico, which allows a maximum of 1 percent of benzene. However, since more than 60 percent of vehicles do not have catalytic converters (models before 1991) it is expected that most of this benzene be emitted through exhaust pipe. Another strategy being implemented is the use of vapor recovery systems at the gas stations. Vehicles emission control technology must be matched with adequate fuel characteristics in the problem area where it will be implemented, to achieve maximum emission reductions.

Personal exposure to benzene, toluene and xylene in different microenvironments at the Mexico City metropolitan zone

The Mexico City Metropolitan Zone (ZMCM) population's exposure to benzene, toluene and xylene was measured at different microenvironments to establish basic indicators of the presence and effects of these characteristic volatile organic compounds (VOC). In particular, VOC personal exposures were measured in different microenvironments during a 5-day working week, with 12-h daily periods. We have found a good agreement of our results with the registered VOC levels of the Metropolitan Automated Monitor System (RAMA) for the corresponding period. From our results, we expect to generate useful information to evaluate the health effects of these VOCs on exposed people.

Sustainability of least cost policies for meeting Mexico City's future water demand

Meeting future water demand without degrading ecosystems is one important indicator of sustainable development. Using simulations, we showed that compared to existing policy, more sustainable water supply options are similar or cheaper in cost. We probabilistically forecasted the Mexico City metropolitan zone population for the year 2015 to be 23.5 million and total required water supply to be 106 m3 s−1. We optimized existing and potential supply sources from aquifers, surface water, treatment/reuse, and efficiency/demand management by cost to meet future supply needs; the applied source supply limits determined the degree of sustainability. In two scenarios to supply 106 m3 s−1, the business‐as‐usual scenario (zero sustainability) had an average relative unit cost of 1.133; while for the most sustainable scenario (it includes reducing potential supply basins' exploitation limits by 50%), the value was 1.121. One extreme scenario to supply the forecast's 95% confidence value (124 m3 s−1) showed little unit cost change (1.106). The simulation shows sustainable policies can be cost‐effective.