| The objective of this work was to develop and assess an automatic procedure
to generate reduced chemical schemes for the atmospheric photooxidation of
volatile organic carbon (VOC) compounds. The procedure is based on (i) the
development of a tool for writing the fully explicit schemes for VOC
oxidation (see companion paper Aumont et al., 2005), (ii) the application of
several commonly used reduction methods to the fully explicit scheme, and
(iii) the assessment of resulting errors based on direct comparison between
the reduced and full schemes.
The reference scheme included seventy emitted VOCs chosen to be
representative of both anthropogenic and biogenic emissions, and their
atmospheric degradation chemistry required more than two million reactions
among 350000 species. Three methods were applied to reduce the size of the
reference chemical scheme: (i) use of operators, based on the redundancy of
the reaction sequences involved in the VOC oxidation, (ii) grouping of
primary species having similar reactivities into surrogate species and (iii)
grouping of some secondary products into surrogate species. The number of
species in the final reduced scheme is 147, this being small enough for
practical inclusion in current three-dimensional models. Comparisons between
the fully explicit and reduced schemes, carried out with a box model for
several typical tropospheric conditions, showed that the reduced chemical
scheme accurately predicts ozone concentrations and some other aspects of
oxidant chemistry for both polluted and clean tropospheric conditions. |