zandoval 

Yes... But not in a way you would normally think. At 2.5 µ your getting close to the size of your red blood cells. Again the problem is these particulates lodging in your tissues and not directly expired. That's one of the problems with Cedar Fever in the south. It's not really an allergy but the size of the Cedar pollen at 1.8 µ actually permeating your lungs and geting into your blood stream. We used to see GI's suffering with cedar fever and concentrations of cedar pollen showing in thier urine under the microscope as shinny little glass type particles.

So are the guidelines to lax? I can't really say. At least we have them. Thank Goodness...

I remember after the forest fires here in Bastrop Texas, weeks after the fires were under control there was still residual smoke in the air. You could ride along and then just stop cause there was heavy smoke in a gully or choking smoke blowing across the road. In general the concentration of the smoke was acceptable for the area but for an individual ridding a bike into a pocket of bad air it was a bugger.

I really do think we are doing better at monitoring our air. And individuals are getting smarter about the air they are breathing... This is reassuring.