Type or paste a DOI name into the text box. Earth by binary option atmos UV radiation from the Sun.
In this chapter we examine the mechanisms controlling the abundance of ozone in the stratosphere and the effect of human influence. The presence of a high-altitude ozone layer in the atmosphere was first determined in the 1920s from observations of the solar UV spectrum. A theory for the origin of this ozone layer was proposed in 1930 by a British scientist, Sydney Chapman, and is known as the Chapman mechanism. It lays the foundation for current understanding of stratospheric ozone. 240 nm can photolyze the O2 molecule. Chemical Kinetics and Photochemical Data for Use in Stratospheric Modeling, JPL Publication 97-4, Jet Propulsion Lab, Pasadena, CA, 1997.
Simple relationships between O2, O, and O3 concentrations can be derived from a chemical steady-state analysis of the Chapman mechanism. 2 , chemical steady state can be assumed for a species if its production and loss rates remain roughly constant over its lifetime. The effective lifetime of O3 against chemical loss is defined by the lifetime of Ox. Center panel: O2 and O3 photolysis rate constants. Right panel: calculated and observed vertical profiles of O3 concentrations.
O3 concentrations at 20-30 km altitude. 2k1, which we have seen is the effective source for O3. In the late 1950s it was discovered that catalytic cycles initiated by oxidation of water vapor could represent a significant sink for O3 in the stratosphere. Water vapor is supplied to the stratosphere by transport from the troposphere, and is also produced within the stratosphere by oxidation of CH4.
Water vapor mixing ratios in the stratosphere are relatively uniform, in the range 3-5 ppmv. We refer to the ensemble of OH and HO2 as the HOx chemical family. Atmospheric chemists were called upon to assess the effects of such a fleet on the O3 layer. This cycling between NO and NO2 takes place on a time scale of about one minute during daytime.
It causes, however, rapid exchange between NO and NO2. Termination of the catalytic cycle involves loss of NOx radicals. Ultimate removal of NOy is by transport to the troposphere where HNO3 is rapidly removed by deposition. The identification of a NOx-catalyzed mechanism for O3 loss turned out to be a critical lead towards identifying the missing O3 sink in the Chapman mechanism. Beyond the source from supersonic aircraft, could there be a natural source of NOx to the stratosphere?
The conversion to N2 is however of no interest for driving stratospheric chemistry. The dominant sink for NOy in the stratosphere is transport to the troposphere followed by deposition. Thus the loss rate of NOy is relatively well constrained, to within a factor of two. Chemical cycling within the NOy family. This ratio can be calculated from the rate equations for the different components of the NOy family. Under most conditions, chemical steady state between the different NOy components is a good approximation.
We therefore have all the elements needed to calculate the O3 loss rate from the NOx-catalyzed mechanism. When atmospheric chemists did these calculations in the 1970s they found that they could fully account for the missing sink of O3 in the Chapman mechanism! 4 that consideration of aerosol chemistry modifies greatly the model results in the lower stratosphere. Ice core data show that atmospheric concentrations of N2O have risen from 285 ppbv in the 18th century to 310 ppbv today, and present-day atmospheric observations indicate a growth rate of 0.
1930s and their use increased rapidly in the following decades. The lifetime of HCl is typically a few weeks and the lifetime of ClNO3 is of the order of a day. In August the ozone hole has not developed yet, while in October it is fully developed. Several aircraft missions were conducted in the late 1980s to understand the causes of the antarctic ozone depletion. O-Cl bond rather than at the weaker O-O bond. Again, this catalytic cycle is made significant by the high concentrations of ClO over Antarctica. Why are ClO concentrations over Antarctica so high?