Systematic reduction of complex tropospheric chemical mechanisms, Part II: Lumping using a time-scale based approach L. E. Whitehouse1, A. S. Tomlin1, and M. J. Pilling2 1Energy and Resources Research Institute, University of Leeds, Leeds LS2 9JT, UK 2School of Chemistry, University of Leeds, Leeds LS2 9JT, UK
Abstract. This paper presents a formal method of species lumping that can be applied
automatically to intermediate compounds within detailed and complex
tropospheric chemical reaction schemes. The method is based on grouping
species with reference to their chemical lifetimes and reactivity structures.
A method for determining the forward and reverse transformations between
individual and lumped compounds is developed. Preliminary application to the
Leeds Master Chemical Mechanism (MCMv2.0) has led to the removal of 734
species and 1777 reactions from the scheme, with minimal degradation of
accuracy across a wide range of test trajectories relevant to polluted
tropospheric conditions. The lumped groups are seen to relate to groups of
peroxy acyl nitrates, nitrates, carbonates, oxepins, substituted phenols,
oxeacids and peracids with similar lifetimes and reaction rates with OH. In
combination with other reduction techniques, such as sensitivity analysis and
the application of the quasi-steady state approximation (QSSA), a reduced
mechanism has been developed that contains 35% of the number of species
and 40% of the number of
reactions compared to the full mechanism. This has led to a speed up of a factor of 8 in terms of
computer calculation time within box model simulations.
Citation: Whitehouse, L. E., Tomlin, A. S., and Pilling, M. J.: Systematic reduction of complex tropospheric chemical mechanisms, Part II: Lumping using a time-scale based approach, Atmos. Chem. Phys., 4, 2057-2081, doi:10.5194/acp-4-2057-2004, 2004.