The important variables in the problem of ozone reduction by nitrogen fertilizers are regarded to be as follows: &tgr;, the atmospheric residence time of nitrous oxide; β, the fraction of nitrogen fertilizer that is denitrified within a few decades; and α, the fraction of denitrified gases that is nitrous oxide. With these three parameters, plus the results f the Climatic Impact Program, the time and the degree of ozone reduction can be estimated by ultrasimple equations which give about the same results as more elaborate model calculations. At the present state of uncertainly concerning the global nitrogen balance this simple approach may be useful in framing working hypotheses for solution of the full problem.<