Sunfish -- Wise advice.
Pace --
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.
As someone living in an area with a huge pollen count every Spring, including now, clear air and blue skies
do not stop me from teary eyes, runny nose, and sneezing, even if I can't see what I'm breathing.
The picture of the tiny vents use to cool the turbine blades gave me pause for thought, as have comments on the possibility of pitot tubes clogging.
After all, isn't the Air France crash in the mid-Atlantic attributed in part to misleading air speed from pitot tubes clogged with ice? What's the difference between ash and ice, aside from clear skies and sunny weather, and the relative (?) ease of switching to VFR?