Abstract
Cross-tropopause transport of O 3 is a significant factor in the tropospheric budget and distribution of O 3 . Nevertheless, the distribution in the troposphere of O 3 that originates from the stratosphere is uncertain. We study this with a chemistry — general circulation model with relatively high spatial and temporal resolution. The model simulates background tropospheric CH 4 -CO-NO x -HO x photochemistry, and includes a tracer for stratospheric O 3 . Since this tracer is not photochemically produced in the troposphere but only destroyed, comparing its budget and distribution with that of total tropospheric O 3 yields an estimate of the contribution of the stratospheric O 3 source in the troposphere. Model results suggest that transport from the stratosphere and net photochemical formation in the troposphere, considering present-day emissions, are of comparable magnitude. The model predicts efficient transport of upper tropospheric O 3 -rich air to the surface by large-scale subsidence in the subtropics and by synoptic disturbances in the NH middle and high latitudes. O 3 from the stratosphere contributes significantly to surface O 3 in winter and spring when the photochemical lifetime of O 3 is relatively long. In summer and in the tropics, little O 3 from the stratosphere reaches the surface due to strong photochemical destruction, so that surface O 3 is largely determined by photochemical production. Photochemically produced O 3 maximizes in the free troposphere where the O 3 surface warming efficiency is higher compared to the boundary layer. DOI: 10.1034/j.1600-0889.49.issue1.3.x
Published Version
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