Atmosphere: an envelope of gases encasing a planet.
Biosphere: is basically all the living parts of the earth's surface, waters, and the living oganism that inhabit those surfaces and waters.
My Answer: One way in which the atmosphere would be impacted in the absense of the biosphere is the loss of oxygen gas in the atmosphere generated by planted in the biosphere during photosynthesis. The atmosphere and biosphere work in harmony creating cycles of life and gas exchanges; every living being eventually dies and decomposes into solid particles and gases that are recycled up into the atmosphere. Therefore, without life much of the gas exchange in the atmosphere would be lost.