This shows a full year of data, from January to December, day numbers lower than the today marker are this year, and those higher are the tail end of last year. Summer is in the middle of the graph
winter on both ends. This might change as the graph is refined. The hour of day axis runs from 6am to 6am - we consider that any interesting nighttime data after midnight really
belongs to the previous day.
Values are clipped at 400, we have seen values higher but it seems best to put all the locations on the same scale rather than auto scaling the height. Colours approximately correspond
to AQIH colours which are defined for a 24 hour mean.