The map shows smoke created by wildfires. It appears that the states of New Mexico, Colorado, and parts of Wyoming, Arizona, and Nebraska are being hit pretty hard.
The red dots are fires, while the smoke is green (thin), yellow (moderately dense), and purple (dense). The Wallow fire in southeast Arizona is responsible for much of the smoke in the central United States.
(Update: on June 6 we posted an updated smoke map.)