Formulation of the cosmic ray–driven electron-induced reaction mechanism for quantitative understanding of global ozone depletion

Abstract

This paper formulates the cosmic ray–driven electron-induced reaction as a universal mechanism to provide a quantitative understanding of global ozone depletion. Based on a proposed electrostatic bonding mechanism for charge-induced adsorption of molecules on surfaces and on the measured dissociative electron transfer (DET) cross sections of ozone-depleting substances (ODSs) adsorbed on ice, an analytical equation is derived to give atmospheric chlorine atom concentration: C l = ∑ i k i θ ODS i Φ e 2 , where Φ e is the prehydrated electron (e pre − ) flux produced by cosmic ray ionization on atmospheric particle surfaces, θ ODS i is the surface coverage of an ODS, and k i is the ODS’s effective DET coefficient that is the product of the DET cross section, the lifetimes of surface-trapped e pre − and Cl − , and the particle surface area density. With concentrations of ODSs as the sole variable, our calculated results of time-series ozone depletion rates in global regions in the 1960s, 1980s, and 2000s show generally good agreement with observations, particularly with ground-based ozonesonde data and satellite-measured data over Antarctica and with satellite data in a narrow altitude band at 13 to 20 km of the tropics. Good agreements with satellite data in the Arctic and midlatitudes are also found. A previously unreported effect of denitrification on ozone loss is found and expressed quantitatively. But this equation overestimates tropospheric ozone loss at northern midlatitudes and the Arctic, likely due to increased ozone production by the halogen chemistry in polluted regions. The results render confidence in applying the equation to achieve a quantitative understanding of global ozone depletion.