The investigation of ion chemistry and the properties of ions and cluster ions is essential for a fundamental understanding of factors that affect atmospheric electrical conductivity. Recent mass spectrometeric observations of ambient stratospheric and tropospheric ions and recent laboratory studies of these ions are reviewed, and our present knowledge of the chemical nature of ions below 50 km is assessed. Some organic species, namely, trimethylamine, pyridine, and methylpyridines, are suggested to participate in the tropospheric positive ion chemistry.