Ozone is very reactive. It easily loses the third oxygen atom in the presence of other highly reactive compounds called radicals, which contain chlorine, hydrogen, nitrogen, or bromine. Minute quantities of these radicals can cause large decreases in ozone because they are not consumed in the reaction. This is called a catalytic cycle.
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 8.0.0.0.0