The page at this link in the webshot command includes ovals to indicate air quality in a particular location
webshot("https://www.purpleair.com/map?&zoom=12&lat=39.09864026298141&lng=-108.56749455168722&clustersize=27&orderby=L&latr=0.22700642752714373&lngr=0.4785919189453125", "paMap.png")
The png that webshot produces doesn't include these ovals. I suspect these are created with javascript and webshot is not picking them up. But I don't know how to tell it to do so, or even if it is possible.