Is the sky clearer early in the morning?

Yes. Several reasons:

A) The diurnal cycle means that pollution production has been reduced for roughly twelve hours, so it has had a chance to disperse.

B) the cooler morning temperatures have allowed some precipitation of excess moisture in the air which condenses around dust particles and thus 'washing' them out of the air.

C) Cooler temperatures due to lack of turbulence-producing solar heating mean less dust lifted into the air by thermals.

As an ex-pilot, I must state that flying is far more pleasant in the early mornings, as the air is cleaner/clearer and there are very few annoying turbulent thermals at that hour of the day.