ON THE LIMITATION OF STEADY-STATE EXPRESSIONS AS TESTS OF PHOTOCHEMICAL THEORY OF THE STRATOSPHERE

A critical testing of atmospheric chemical theories requires the simultaneous measurement of many species and often a measurement of a photolysis coefficient. Following on from the work of HARRIES [(1982), Stratospheric composition measurements as tests of photochemical theory. J. atmos. terr. Phys. 44, 591] the required accuracy for these simultaneous measurements has been calculated using a photochemical diurnal model. The steady-state expressions for NO2 and HNO3 are investigated throughout the stratosphere. Calculations show that, if all observable parameters are measured to + 10%. a lest to +/- 20% can be made. Further work has shown the inadequacy of the HNO3 and HCl steady-state assumptions at certain altitudes and solar zenith angles. By calculating a rate ratio, defined as the rate of production divided by the rate of loss of a species, steady-state assumptions can be tested. An evaluation of chemical life-time, which is normally considered, does not allow a quantification of departures from steady-state. We show that the rate ratio is a useful parameter to do this. Using this approach we have verified the HCl steady-state assumption near 40 km at the time and location of the Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment. Based on this verification a CIO mixing ratio of 0.5 ppbv was derived using ATMOS measurements. This derived value agrees well with other observations.