From the U.S. Environmental Protection Agency (EPA) : https://www.epa.gov/pm-pollution
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(1) Monitor Information is displayed when cursor is hovered over a monitor icon on the map
URL updated as monitors selected/removed in order to share selected monitors
(2) Selected monitors listed below here
Hover cursor over "Hourly NowCast" graph to see additional information
(3) Click "x" button to remove selected monitor
(4) Click "NEXT" button to see additional graphics for selected monitors