To cut the story short, as I really don’t have time to write endless posts, this is how the Canary Islands looked like from space on the 6th of May,
and this is what the same satellite (MODIS Aqua) saw after they got covered by sand from Africa (image from the 12th of May, credits: NASA/GSFC, MODIS Rapid Response):
The dust concentration went up from ~0.1-0.5 µgr/m3 to 36 µgr/m3. (The position of the Sun is also a bit different on the two pictures above, lowering the contrast on the bottom one, but believe me, what you see there is mostly sand from the desert.) So this means a hundred times more dust in the atmosphere! And it was really noticeable just by looking around. Everything seemed to be behind a thin layer of yellowish fog… Of course this had a very bad effect on the transparency of the sky, making the observation very difficult during the last two nights. To make things worse, the humidity was also high, and the moonlight is also getting quite disturbing as we are moving closer to full moon. Tonight the humidity is back at ~10% and the dust concentration fall down to 1/10th of its peak value, so life is a bit easier now :)