The US PM Air quality map (left below) shows many areas of elevated PM AQI. The most significant is in the lower Lake Michigan area and this region is under cloud so the source is not apparent. But smoke from fires near the Great Slave Lake in Nunuvut in northern Canada have been pouring southward for a week now. The midweek pulse of smoke which penetrated the prairie states apparently is curled up under a weather system centered near Chicago. One has to expect that an appreciable fraction of these aerosols may be due to widespread fireworks displays on the 4th of July. To the northeast of Chicago, the GASP loop shows a filament of smoke heading towards the mid-Atlantic states.
That smoke has not yet reached Maryland and we have a Chamber of Commerce day on Saturday in Baltimore.
Since early last week, a continual stream of dust from Africa has been entering the Caribbean and some of the PM AQI may be due to Saharan dust. Unfortunately, the throughput on the CALIPSO expedited images has now gotten to about a two day latency and CALIPSO's usefulness in analysing today's haze is limited. But the image form Thursday shows that a broad elevated dust plume was seen over Cuba down through the Antilles.
The Southern Louisiana WaveSite Aeronet Station (below left) shows highly elevated AOD on Saturday afternoon and the color ratios between the six channels would indicate very large particles. A similar signal is seen at Key Biscayne in South Florida (below right). This is more evidence of dust coming into the southeast.
Update: July 6, 2014, 20:30 EDT
Another day of Calipso images are in and that large mid-Atlantic dust plume keeps on coming. On July 5, at 47W and 20N there is a 4 km deep plume of dust. NOAA's HYSPLIT trajectory shows that the lowest levels of the plume (about 1km or 3300') are likely to turn northward before they reach Florida but that the mid levels (3 and 4 km) will just keep churning west into the western Caribbean. It is likely that Saharan dust will continue to affect the southern coastal states.