Chempath 1.0: an open-source pathway analysis program for photochemical models

Abstract

We describe the development of Chempath, an open-source pathway analysis program for photochemical models. This algorithm can help understand the results of complex photochemical models by identifying the most important reaction chains (pathways) for the production and destruction of a species of interest in a reaction system. The algorithm can also quantify the contributions of the pathways to the production and destruction of a species. Chempath is an open-source Python re-implementation of the algorithm developed by . However, Chempath does not include the balance of concentration changes and reaction rates that Lehmann's algorithm uses to eliminate imbalances due to numerical errors. Instead, Chempath quantifies the contributions of these imbalances to the production and destruction of a species. We demonstrate how to apply Chempath to both a simple box model and a one-dimensional photochemical model, using a reaction system for Earth's present-day atmosphere. Chempath can identify well-known chemical mechanisms for O3 production and destruction in these models, suggesting that this algorithm can be applied to understand photochemical models of less-well-known atmospheres, like past and exoplanet atmospheres.