A stratospheric source of reactive nitrogen in the unpolluted troposphere

Abstract

A GFDL 3‐D global generalized tracer field is adapted to provide a preliminary simulation of the reactive nitrogen (NOY) climatology in an unpolluted troposphere which has, as its sole source, downward transport of stratospheric NOY. The tracer field is scaled so that its downward cross‐tropopause flux is balanced by the stratospheric production of NOY. While the model results show stratospheric NOY to be a significant source for the remote troposphere, they do not rule out additional contributions from either the long‐range transport of combustion NOY or the insitu production by lightning. The model NOY climatology in the unpolluted troposphere shows a strong interhemispheric asymmetry due to greater downward NOY flux in the northern hemisphere and a steep drop off to a minimum in the tropics resulting from a combination of model features (tropical rain‐belt, ITCZ, and Indian monsoon) which have been well documented in the real atmosphere.