New Directions: Are we prepared for a wet MIRAGE?

摘要

The impact of megacities (populations larger than 10 million) on global climate has been discussed in a previous New Directions article (PJ. Crutzen, 2004, "New Directions: The growing urban heat and pollution "island" effect—impact on chemistry and climate", Atmospheric Environment 38, 3539-3540) that also mentioned the research initiative, "Mega-city Impact on Regional and Global Environment" (MIRAGE) at the National Center for Atmospheric Research. The objective of MIRAGE is to study the transport and transformation of pollutants from megacities by conducting field projects and utilizing numerical models of different complexities. (http:// www.ucar.edu/communications/quarterly/spring99/ MIRAGE.html). The first of these field programs will take place in February and March, 2006, in the region of Mexico City. This time of the year, Mexico's dry season, was chosen to avoid convection and clouds. Hence, the transport and dispersion of pollutants will be determined primarily by the development of the boundary layer, the magnitude of the mesoscale circulations and the influence of the synoptic-scale systems. The areas most affected by the pollutants will be those within 500 km, given the weak circulation in tropical regions and the limited vertical transport during this time period.