Rivals of the Clouds by Raoul Whitfield — Read

Zooming through a clinging, blinding fog, Lieutenant Adams flew straight into a death trap of flashing enemy planes and flaming, stuttering machine guns. This is an epic of the skies told by the ace of war writers.

There was plenty of it, this gray, clinging fog. Drifting slowly down the slope just west of the tiny pursuit squadron field, clinging to the branches of the gaunt trees, then sweeping out over the field itself, the fog moved. It hung within ten or fifteen feet of the soft earth, and it was thick. Thick and cold. Twenty minutes ago there hadn't been any sign of it; now the barracks could not be seen from the nearest camouflaged hangar.