Southern California experienced moderate levels of PM2.5 and moderate to unhealthy levels of ozone today. Moderate levels of PM2.5 were also observed in the Plains States, Southeast and in the southern part of the Mississippi Valley region.
Fires were reported by the HMS team at NOAA and some of the smoke could be observed over the Mississippi Valley states with MODIS Terra (bottom, left).
The Eyjafjallajökull volcano seems to have affected the air quality in some cities like Le Havre in France. The last image shows a composite of today's Terra image over Northwestern Europe and Le Havre air quality information from the Air Quality Now in Europe website. We see that yesterday they recorded moderate levels of SO2 but as of 1:00 UTC the levels are low again.
The Norwegian Institute for Air Reseach shows a simulation of the volcanic ashes dispersion over Europe. You can see the video here.