I did not see the air of Santiago that bad for a long time.
The mayor of the Santiago declared an "alerta ambiental", which means restrictions on 1/3 of cars without catalytic exhaust pipe, prohibition to burn wood, and advice to avoid physical exercise for all:
Intendencia RM @IntendenciaRM 7h Alerta ambiental para este domingo 29 afecta a vehículos s/sello verde 5 y 6. Prohibido encender calefactores a leña intendenciametropolitana.gov.cl/n10151_29-05-2… via Twitter Web Client
It is bad (and indeed according to the standards of North America this is the worst category) but note how this situation is only half way in the scale of categories of pollution alert for Chile: