There are a variety of other issues related to dealing with such large simulations, beyond today's numerical solver problems. Not least is the challenge of constructing a complete set of all these important species and reactions (and to identify and debug any omissions). Another major challenge is coming up with accurate kinetic parameters for so many reactions, as discussed in the rest of this paper. Because of these difficulties, some researchers have built reduced models, using techniques such as Structure-Oriented Lumping or the Fragment Method to partially overcome the combinatorics. Further work is needed to better understand the errors introduced by these model-reduction approximations, and to automate these methods to make them easy to use.