Air Pollution Index for Beginners

So, I wake up to a rainy day, which is not so unusual, I think of fog over the bay as I am looking out my window this week, but the boys came home from school yesterday talking about the API of 164, which meant no Cross Country practice for Ellis and no running during PE.  I guess that's not fog outside. The girls and I need to add masks to our umbrella staple!
I googled the API after Forrest told me one of his friends at school, who is from Bejing, said the rules in Bejing are a little different because they would never get to go outside if people got worried over an API over 100.  This is what I found in the trusty WSJ. 

Hong Kong air pollution reached extreme highs this week, turning Victoria Harbor a soupy gray and prompting government warnings for residents to stay indoors.

On Thursday morning in the crowded shopping district of Causeway Bay, pollution levels hit a high of 187 on the local air-pollution index. When the city’s levels of air pollution are that high, the government recommends that children, the ill and the elderly try to stay inside. Health experts say that level of air pollution can trigger  heart attacks or strokes.