Spoke with a met at work who specializes in pollution of all things. They said in a briefing today you really need the equivalent of about 0.25" of rain before the air is cleaned out.
100% violets. If you want to mitigate them without harsh chemicals, try removing all the mulch, put down a dense layer of newspaper, then 3 to 4 inches of mulch. It will work well for a year or two.