We made a little app visualizing the air quality/polution in Mexico City with data provided by datos.labplc.mx. The API of Laboratorio De Datos unfortunately provides only 5 data points in the city in real time. But it gives you a pretty good idea when things get dirty.
Here is the permanent link: BADAIR by Pedro&Juana
LEGEND of air quality
Muy Mala [very bad]
Extremamente Mala [horrific]