Mexico City drastically reduced air pollutants since 1990s most polluted city Mexico City drastically reduced air pollutants since 1990s comprehensive approach to improve their air quality comprehensive approach to improve their air quality Mexico City Mexico City drastically reduced air pollutants since 1990s Mexico City drastically reduced air pollutants since 1990s most polluted city unlikely example impressive reduction Mexico it is claimed Wash Post Mexico City drastically reduced air pollutants since 1990s unlikely example Mexico City drastically reduced air pollutants since 1990s Mexico City drastically reduced air pollutants since 1990s