Sunfish
I was flying a business jet up north hours before the airspace was closed if you PM me I will give you a link to a video I made from the cockpit.
Beautiful day 100 miles vis at FL250 with well pronounced and broken cumulus well below.
The MK1 eyeball is the best way of detecting particles either water or dust. Clear air is clear air. I find it hard to understand claims of invisible.
Pollution in dust form is visible to pilots either as a haze or thin cloud and usually with a slight colouration.
I take your point on looking vertically but horizontally NO unless of course your in cloud or flying at night.
Did the various groups involved do their best within the regs without doubt
Were we victims of our own burocracy possibly? I also take the point of hindsight and could things have been done differently.
Regardless there will be finger pointing as the huge cost and who bears it hits the courts.
Pace