We obtain nitrogen abundances in the H ii regions of selected spiral galaxies by using a new algorithm developed from grids of photoionization models. The new method requires only the observation of optical [N ii], [O ii] and [O iii] lines. We show the self-consistency of the new method, and also the agreement with more detailed modelling of individual H ii regions. Gradients in [N/O] against effective radius and [O/H] are presented for a well-observed subset of galaxies from the Vila-Costas & Edmunds sample.
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Thurston et al. (1996) studied this question.