In spite of these achievements, local authorities acknowledge that additional efforts are needed to reduce the level of pollutants that are still beyond the national standards such as ozone and particulate matter. The measures adopted to improve air quality have been diverse, from closing the most polluting factories to banning cars in the metropolitan area one day per week through the Hoy No Circula programme (“No driving today”). Mexico City’s government has introduced the Atmospheric Monitoring Network (Red de Monitoreo Atmosferico, SIMAT), which provides data for informed policy making and has led to the adoption of the Metropolitan Index of Air Quality, and the establishment of contingency and pre-contingency protocols.