CONDENSING COMPLEX ATMOSPHERIC CHEMISTRY MECHANISMS - 1 - THE DIRECT CONSTRAINED APPROXIMATE LUMPING (DCAL) METHOD APPLIED TO ALKANE PHOTOCHEMISTRY

Atmospheric chemistry mechanisms are the most computationally intensiv e components of photochemical air quality simulation models (PAQSMs). The development of a photochemical mechanism, that accurately describe s atmospheric chemistry while being computationally efficient for use in PAQSMs, is a difficult undertaking that has traditionally been purs ued through semiempirical (''diagnostic'') lumping approaches. The lim itations of these diagnostic approaches are often associated with inac curacies due to the fact that the lumped mechanisms have typically bee n optimized to fit the concentration profile of a specific species. Fo rmal mathematical methods for model reduction have the potential (demo nstrated through past applications in other areas)to provide very effe ctive solutions to the need for computational efficiency combined with accuracy. Such methods, that can be used to ''condense'' a chemical m echanism, include ''kinetic lumping'' and ''domain separation''. An ap plication of the kinetic lumping method, using the direct constrained approximate lumping (DCAL) approach, to the atmospheric photochemistry of alkanes is presented in this work. It is shown that the lumped mec hanism generated through the application of the DCAL method has the po tential to overcome the limitations of existing semiempirical approach es, especially in relation to the consistent and accurate calculation of the time-concentration profiles of multiple species.