NO and NO 2 produced in the atmosphere by lightning have been observed and measured. Detailed observations of NO x concentrations and storm activity have been recorded. In the presence of ozone at ≈ 30–50 ppb, the NO produced is rapidly oxidized to NO 2 . The NO x resulting from an individual flash of lightning, as well as from numerous area-wide lightning flashes have been measured. It is estimated that, at least in the observed storm, a flash of lightning produced 4 × 1026 molecules of NO x , with an uncertainty of from one-fourth to twice that amount.