Air quality policies based on scientific information have proved to be
effective for controlling air pollution and protecting public health.
Intensive field studies provide knowledge that combined to data from
emission inventories and air quality monitoring allows to understand the
causes that trigger air pollution and catalyze the design of effective
control measures. We review the case of Mexico City, where past
international collaborative studies were fundamental to improve air
quality, but a null progress and a possible reversal to high air
pollution levels in recent years suggest that a new dedicated field
measurement campaign is urgently needed.