>>19088674 /LB
Ya, I don't know, but this is one map showing the concentrations from yellow (bad) to red (really bad).
https://gispub.epa.gov/airnow/?showgreencontours=false&xmin=-13648824.845239772&xmax=-4256242.809559809&ymin=3271222.7385867233&ymax=7287529.952801958
Their explanation blaming Canadian forest firs is bull shit.