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jamesqf -

Originally Posted by jamesqf

That map really puzzles me. I don't see anything on the source, but if it's recent, say the last couple of months, there's a more likely explanation than diesel for most of the areas west of the Rockies, and that's all the forest fires. Most of California was smoked out for a month or more.

And the rest of those red areas, like northwestern Utah. Why are they so high? Maybe all those speed record attempts on the Bonneville Salt Flats, you suppose? The northern corner of Montana, and south central Oregon? Areas not exactly noted for a lot of diesel engines, but with a lot of forest or rangeland subject to fires.

It's from 2006 :

Area Designations for 2006 24-Hour Fine Particle (PM2.5) Standards | US EPA

CarloSW2