"crystal clear air" is correct and usable in written English.
You can use this phrase when you are describing a moment of clarity or a moment of freshness, such as, "I took a deep breath of the crystal clear air and felt refreshed."
When I hear the heady seasonal waltz of Someone Somewhere in Summertime and the hushed, hymnal Big Sleep I think of mountains, altitude, beams of sunlight, crystal waters, clear air and artistic ambition triumphing over commercial demands.
A high note leaped out, parping and cutting crystal clear through the air.
The new president also wants to roll back the Environmental Protection Agency while having "crystal clear" water and clean air.
Trump has since modified his stance on the EPA, stressing that he supports clean air and "crystal clear, crystal clean" water but not programs that combat climate change.
But, in September, he back-tracked on that statement, saying he supports clean air and "crystal clear, crystal clean" water.
A lookout of ancient dolerite rock facing the Cradle Mountain world heritage area, it captures Tasmania's essence: remote, spectacular with crystal clear views through pure air from the Roaring Forties that pound the island's west coast.
"In a surprisingly short time, after being disconnected from the digital word, people go back to what is more natural for us all, which is to connect with nature, to appreciate unpolluted air and crystal clear water, to hear the sounds of birds and the breeze passing through the trees, and at night discovering more stars than one could ever hope to see in the city," said owner Norm Dove.
It was unbelievable – because of the low temperature the air was crystal clear, the sun was rising from the water, our black diving suits contrasting with the white snow," he said.
The air is crystal clear with absolutely mind-boggling landscapes, delicious food, amazing aurora and magical light," said Tom. "So long as you have the right attire, and there's a fire in the house, one can tolerate the weather".
