Mass spectrometric measurements of naturally occuring atmospheric ions were performed near ground level at Sapelo Island, Georgia. The sampled ions were then passed through a chamber in which they could be dissociated by multiple collisions with a buffer gas. At low-collision energies, H2O clusters were removed, allowing positive core ions to be identified at masses 18, 60, 80, 94, and 108. At high-collision energies, positive core ions were dissociated, and the mass of their fragments was used to help determine their identity. Mass 18 is believed to be NH4+. Methylpyridine and dimethylpyridine were tentatively identified as the parent neutral species responsible for the core ions observed at mass 94 and 108.