1. The conversion of nitrite or nitrate to gaseous end products NO, N2O, and N2 by denitrifying bacteria. Molecular nitrogen, N2, is the most abundant end product. The oxidized forms of N (nitrate, nitrite, nitric acid, nitric oxide, and nitrous oxide) serve as alternative electron acceptors in the absence of sufficient oxygen; thus, denitrification is primarily an anaerobic process. 2. The removal of active nitrogen from the atmosphere through uptake into particles. The term is particularly used in context with the irreversible uptake of nitric acid into ice clouds (polar stratospheric clouds) in the antarctic stratospheric vortex. This reduction in the level of active nitrogen allows ozone depletion by chlorine oxides to occur unchecked.