Comparison of tropospheric gas-phase chemistry schemes for use within global models K. M. Emmerson and M. J. Evans School of Earth & Environment, University of Leeds, Leeds, LS2 9JT, UK
Abstract. Methane and ozone are two important climate gases with significant
tropospheric chemistry. Within chemistry-climate and transport models this
chemistry is simplified for computational expediency. We compare the state
of the art Master Chemical Mechanism (MCM) with six tropospheric chemistry
schemes (CRI-reduced, GEOS-CHEM and a GEOS-CHEM adduct, MOZART-2, TOMCAT and
CBM-IV) that could be used within composition transport models. We test the
schemes within a box model framework under conditions derived from a
composition transport model and from field observations from a regional
scale pollution event. We find that CRI-reduced provides much skill in
simulating the full chemistry, yet with greatly reduced complexity. We find
significant variations between the other chemical schemes, and reach the
following conclusions. 1) The inclusion of a gas phase
N2O5+H2O reaction in one scheme and not others is a large
source of uncertainty in the inorganic chemistry. 2) There are significant
variations in the calculated concentration of PAN between the schemes, which
will affect the long range transport of reactive nitrogen in global models.
3) The representation of isoprene chemistry differs hugely between the
schemes, leading to significant uncertainties on the impact of isoprene on
composition. 4) Differences are found in NO3 concentrations in the
nighttime chemistry. Resolving these four issues through further
investigative laboratory studies will reduce the uncertainties within the
chemical schemes of global tropospheric models.
Citation: Emmerson, K. M. and Evans, M. J.: Comparison of tropospheric gas-phase chemistry schemes for use within global models, Atmos. Chem. Phys., 9, 1831-1845, doi:10.5194/acp-9-1831-2009, 2009.