Megacities are very large urban agglomerations with populations that exceed 10 million inhabitants, differing from urban areas not only in population size but also in the scale of their economy, infrastructure and associated environmental impacts (Gurjar and Lelieveld, 2005). Rapid urbanization has resulted in increasing air pollution emissions, typically arising from transportation, energy production and industrial activities, concentrated in densely populated areas (Gurjar et al., 2008) and surpassing the limits of the megacities' physically occupied area, thus contributing significantly to air quality on a global scale through the long range transport of air pollutants (Gurjar and Lelieveld, 2005; Butler et al., 2008; Butler and Lawrence, 2009).
This work was developed within the framework of the interAmerican project “South American Emissions, Megacities and Climate” aimed at developing a number of tools for the chemical