An estimate of the flux of stratospheric reactive nitrogen and ozone into the troposphere

Abstract

The globally averaged net downward annual fluxes of reactive nitrogen (NO_y) and O₃ from the stratosphere are estimated using observed correlations of N₂O with NO_y and O₃. The linearity of the observed correlations in the lower stratosphere allows the downward fluxes of NO_y and O₃ to be related to the upward flux of N₂O. The upward flux N₂O can be calculated from a mass balance and stratospheric photochemistry. In this way, the complicated photochemistry and transport of NO_y and O₃ can be bounded by a much simpler calculation involving N₂O. The estimated NO_y net flux of 0.45 Tg (N) yr⁻¹ (range 0.23–0.73) is slightly less than previous estimates, but within the range of uncertainty. Precipitation of NO_y from the Antarctic winter stratosphere may be a significant fraction of the annual global flux out of the lower stratosphere. The global budget for stratospheric NO_y shows that an N₂O lifetime greater than 160 years is inconsistent with extensive mass flow through the Antarctic winter vortex. The estimated O₃ flux of 3.5×10¹⁰ molecules cm⁻² s⁻¹ (range 1.5–6.8) agrees well with previous estimates using completely independent techniques.