期刊名称：Tellus A: Dynamic Meteorology and Oceanography
电子版ISSN：1600-0870
出版年度：1999
卷号：51
期号：1
页码：123-146
DOI：10.3402/tellusa.v51i1.12310
摘要：We present a largely tutorial overview of the main processes that influence the photochemistry ofthe background troposphere. This is mostly driven by the photolysis of ozone by solar ultravioletradiation of wavelengths shorter than about 340 nm, resulting in production of excited O(1D)atoms, whose reaction with water vapor produces OH radicals. In the background atmospherethe OH radicals mostly react with CO, and with CH4 and some of its oxidation products, whichin turn are oxidized by OH. Depending on the availability of NOx catalysts, ozone may be producedor destroyed in amounts that are much greater than the downward flux of ozone from the stratosphereto the troposphere. Using the 3D chemical-transport model MATCH, global distributionsand budget analyses are presented for tropospheric O4, CH4, CO, and the ‘‘odd hydrogen’’ compoundsOH, HO2 and H2O2. We show that OH is present in maximum concentrations in thetropics, and that most of the chemical breakdown of COandCH4 also occurs in equatorial regions.We also split the troposphere into continental and marine regions, and show that there is a tremendousdifference in photochemical O3 and OH production for these regions, much larger than thedifference between the northern hemisphere and southern hemisphere. Finally, we show the resultsfrom a numerical simulation in which we reduced the amount of ozone in the model stratosphereby a factor of 10 (which in turn reduced the flux of O3 into the troposphere by about the samefactor). Nevertheless, for summer conditions, model calculated O3 mixing ratios below 5 km in themid to high latitudes were about 70–90% as high as those calculated with the full downward fluxof ozone from the stratosphere. This indicates that, at least under these conditions, O3 concentrationsin the lower troposphere are largely controlled by in situ photochemistry, with only a secondaryinfluence from stratospheric influx.
