Countries the world over, especially in the developing world, are experiencing rapid urbanization. The share of the world’s population living in cities is reported to have grown from about 35 percent in 1970 to almost 50 percent in 2001, and this number is expected to increase to more than 60 percent by 2030 (UN-HABITAT 2001). One of the many consequences of the increased economic activity that accompanies urbanization—particularly increased vehicle use, electricity generation, and industrial production—is the deterioration of air quality (Molina 2004)
