Whereas . cities have seen dramatic improvements in air quality over the last three decades1, Mexico City has been considerably less successful. Levels of major air pollutants in Mexico City routinely exceed maximum exposure limits established by the World Health Organization (WHO). For example, the WHO has warned that eight-hour average ozone levels exceeding 100 micrograms per cubic meter threaten human health. 2 During the period 1986-2005, this guideline was exceeded in Mexico City for 92% of all days. A large literature documents the social cost of air pollution (., Dockery, et al. 1993, Pope 1995, Chay and Greenstone 2005). Airborne pollutants have been linked to respiratory infections, chronic.
