Can atmospheric humidity act as a cloud chamber?
Certainly the cosmic rays passing supersaturated volumes on the high atmosphere ionize the atmossphere and help create clouds.
In its 10 years of operation, CLOUD has made several important discoveries on the vapours that form aerosol particles in the atmosphere and can seed clouds. Although most aerosol particle formation requires sulphuric acid, CLOUD has shown that aerosols can form purely from biogenic vapours emitted by trees, and that their formation rate is enhanced by cosmic rays by up to a factor 100.
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Now if you can use a camera on a balloon to take pictures of cosmic ray tracks is not clear. Maybe if the time of day is chosen carefully that the sun would shine through the tracks? Certainly it would not be worth the effort. Look how to make a cloud chamber here. Special conditions are necessay to see or record such tracks.