Physica A 391 (2012) 606–615 Contents lists available at SciVerse ScienceDirect Physica A journal homepage: www.elsevier.com/locate/physa Upscaling pollutant dispersion in the Mexico City Metropolitan Area Francisco J. Valdés-Parada ∗ , Juan R. Varela, José Alvarez-Ramirez Departamento de I.P.H., Universidad Autónoma Metropolitana-Iztapalapa. Av. San Rafael Atlixco 186, Col. Vicentina, 09340, México, D.F., Mexico article info Article history: Received 15 December 2010 Received in revised form 5 July 2011 Available online 25 August 2011 Keywords: Pollutant dispersion Upscaling Volume averaging Mexico City abstract Pollutant emission is an important problem in megacities such as Mexico City, imposing serious threats to human health and economic activity. Public policies oriented to deal with pollutant management ought to be based upon a close understanding of the trans- port mechanisms involved in the commonly complex network of streets and buildings. Modeling and simulation tools have proved to be useful for understanding field measure- ments and developing efficient monitoring strategies. The aim of this work is to provide estimations of the (longitudinal and transverse) dispersion coefficients in upscaled mod- els for pollutant transport in the Mexico City Metropolitan Area (MCMA). To this end, we use the method of volume averaging, which allows calculation of the dispersion coeffi- cients by solving the associated closure problems in some representative regions of the MCMA. The results show that local geometry has an important effect upon contaminant dispersion, especially in the direction that is transverse to the pressure gradient. This sug- gests that, although winds can remove an important amount of atmospheric contaminants, high transversal dispersion can help in a fast spreading of contaminants within the street network. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The Mexico City Metropolitan Area (MCMA) is located over a basin with an elevation of 2240 m above the sea level. The region is surrounded on three sides by mountain ridges (e.g., Ajusco Sierra), although a broad north opening and a narrower south–southwest gap are also located at the border of the basin. The population and urbanized area have experienced severe increments in the last decades; simultaneously, the amount of industry has expanded in the same region as a consequence of economic growth. In fact, in the last 50 years, the population has increased up to 18 million inhabitants in 2000 and the metropolitan urbanized area has expanded to about 1500 km 2 . The combined activity of vehicles and industries consumes more than 40 million liters of petroleum fuel daily, yielding thousands of tons of pollutants. Moreover, at peak activity hours, the number of on-road vehicles around commercial and industrial zones becomes very big, leading to severe traffic jams, and the emission of primary pollutants is enhanced. On the other hand, the weather and topographical conditions (e.g., high altitude and tropical isolation) together with the presence of primary pollutants promote the production of secondary contaminants (e.g., ozone), and the formation of particulate matter [1]. Continuous exposure to these conditions constitutes a serious danger to human health, with potential negative consequences to economic productivity and city functionality. The MCMA typical day period is characterized by huge pollutant emission rates with mean particle residence time in the urban basin going up to 12 h [2–4]. The meteorological conditions in the MCMA play a fundamental role in pollutant dispersion, since the dominant winds are able to remove large amounts of particulate matter from the city basin [5]. Stable conditions at night lead to a bad air quality buildup, which causes negative effects on the air quality on the following day. ∗ Corresponding author. Tel.: +52 55 58044648; fax: +52 55 58044900. E-mail address: iqfv@xanum.uam.mx (F.J. Valdés-Parada). 0378-4371/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.physa.2011.08.017