a reaction that takes any atom away from another chemical species. Classical examples in atmospheric chemistry are the gas phase removal of hydrogen from methane by hydroxyl radical or the following solution phase reaction: HSO3- + H2O2 ---> HSO4- + H2O | [Graedel, T.D. and Paul Crutzen. Atmospheric Change: an Earth system perspective; 1993; Freeman Press.] [Atmospheric Environment; v39; 7667-7688; 2005.] [Atmospheric Environment; v32; 3393-3402;1998.]