Low temperatures after sudden stratospheric warming lead to atypical atmospheric composition
The temporal evolution of all chlorine contained in ClONO2, HCl and ClO in northern winter 2009 differs only weakly from that in other years (top panel). The fraction of ClONO2, however, is remarkably larger in February 2009, after the sudden stratospheric warming on January 24. The increase of ClONO2 happened at the expense of HCl (lower panel).
Also record high ozone was observed and attributed to the fact that low temperatures favour a greater O3/O ratio. This ratio controls the active chlorine partitioning and leads to larger abundances of ClO, resulting in the large ClONO2 amounts observed.
For more details see: http://onlinelibrary.wiley.com/doi/10.1002/2014JD021698/pdf