Nitrogen fertiliser and stratospheric ozone: latitudinal effects

Abstract

Substantial increases in atmospheric nitrous oxide (N₂O) resulting from increased use of nitrogen fertilisers might cause large (to 10%; ref. 1) and unacceptable decreases in the stratospheric ozone content^1–3. Such ozone decreases would be caused by catalytic reaction cycles involving odd-nitrogen (NO_x ≡ NO + NO₂) which is formed by N₂O decomposition in the upper stratosphere¹. However, Turco et al.⁴, using a background chlorine level of 2 p.p.b.v. (parts per billion by volume), show that if the recently measured values of the reactions in Table 1 are used, a 50% increase in N₂O would lead to a 2.7% increase in the stratospheric column density, although the ozone content above 30 km would be reduced by > 5% they also estimated (unpublished data) that the change in the ozone column density caused by doubling the N₂O abundance would be very close to zero (within about 0.1%). Here we extend these calculations of N₂O/ozone effects to two dimensions, thereby delineating the latitudinal dependence expected for such ozone perturbations; we also discuss the effects of changes in stratospheric chlorine levels (Cl_x ≡ Cl + ClO + HCl) on predicted ozone changes.