Twelve stations, one city's air

Try this

Select Dingling, a station in the northern hills, then Dongsi in the city center. The calendars look alike: episodes cover the whole city. Dongsi's mean runs about a third higher.
Brush the high end of the wind axis. Almost every windy day is a clean day, at every station.
Select Winter in the box plot and look at the calendar: winter is clean most days and terrible on a few.

Station means compare locations over the same days, but stations miss different days during outages.