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We re-examine the available data on nitrogen and oxygen abundances deduced from the spectra of giant H II regions in external galaxies. If account is taken of the likely differences in temperature between the O II and O III ionization zones, the derived N/O ratios as a function of O/H can consistently be explained by models in which nitrogen has both a (delayed) primary and a secondary component relative to oxygen, with the secondary component dominating at high abundance. There is also some evidence that the secondary component is delayed (by perhaps 2×10 9 yr), and that there is some spread in the ages of the discs of late-type spirals
Vila-Costas et al. (Mon,) studied this question.