Does Cosmic-Ray-Induced Heterogeneous Chemistry Influence Stratospheric Polar Ozone Loss?

Cosmic-ray (CR) -induced heterogeneous reactions of halogenated species have been suggested to play the dominant role in causing the Antarctic ozone hole. However, measurements of total ozone in Antarctica do not show a compact and significant correlation with CR activity. Further, a substantial CR-induced heterogeneous loss of chlorofluorocarbons is incompatible with multiyear satellite observations of ${\mathrm{N}}_2\mathrm{O}$ and CFC-12. Thus, CR-induced heterogeneous reactions cannot be considered as an alternative mechanism causing the Antarctic ozone hole.

Figure 1

Relation between cosmic-ray intensity (from Ref. 17) and mean total column ${\mathrm{O}}_3$ for October poleward of 60°S for 1990–2005 (from Refs. 27, 28). Dashed line shows the linear fit to all data points, dotted line shows the linear fit to the data points excluding 2002 (column ${\mathrm{O}}_3$ 311 DU). We assume an upper limit of the uncertainty of the mean total ${\mathrm{O}}_3$ of 5%.

Figure 2

Time series of ACE-FTS satellite measurements of CFC-12 (top) and ${\mathrm{N}}_2\mathrm{O}$ (middle) as well as the CFC-12 anomaly relative to ${\mathrm{N}}_2\mathrm{O}$ (bottom) at 18.5 km, monthly averaged poleward of 60°S. September data are marked by filled circles. The CFC-12 anomaly is deduced by first calculating from ACE-FTS data poleward of 60°S between 10 and 25 km an empirical relation: ${\mu }_{\mathrm{CFC}\mathrm{\text{−}}12}=4.77+0.558{\mu }_{{\mathrm{N}}_2\mathrm{O}}+0.00741({\mu }_{{\mathrm{N}}_2\mathrm{O}}{)}^2-1.31\times {10}^{-5}\times ({\mu }_{{\mathrm{N}}_2\mathrm{O}}{)}^3$, where ${\mu }_{{\mathrm{N}}_2\mathrm{O}}$ and ${\mu }_{\mathrm{CFC}\mathrm{\text{−}}12}$ are volume mixing ratios in parts per billion (ppbv) and parts per trillion (pptv), respectively. Then, the CFC-12 anomaly is calculated for each data point as the difference of the observed CFC-12 and CFC-12 derived from the correlation using the observed ${\mathrm{N}}_2\mathrm{O}$. The latitude of the ACE-FTS observations in September is $74°\pm 6°\mathrm{S}$ due to the satellite’s viewing geometry.