SALSA2.0: The sectional aerosol module of the aerosol–chemistry–climate model ECHAM6.3.0-HAM2.3-MOZ1.0

Abstract. In this paper, we present the implementation and evaluation of the

aerosol microphysics module SALSA2.0 in the framework of the

aerosol–chemistry–climate model ECHAM-HAMMOZ. It is an alternative

microphysics module to the default modal microphysics scheme M7 in

ECHAM-HAMMOZ. The SALSA2.0 implementation within ECHAM-HAMMOZ is evaluated

against observations of aerosol optical properties, aerosol mass, and size

distributions, comparing also to the skill of the M7 implementation. The

largest differences between the implementation of SALSA2.0 and M7 are in the

methods used for calculating microphysical processes, i.e., nucleation,

condensation, coagulation, and hydration. These differences in the

microphysics are reflected in the results so that the largest differences

between SALSA2.0 and M7 are evident over regions where the aerosol size

distribution is heavily modified by the microphysical processing of aerosol

particles. Such regions are, for example, highly polluted regions and regions

strongly affected by biomass burning. In addition, in a simulation of the

1991 Mt. Pinatubo eruption in which a stratospheric sulfate plume was formed,

the global burden and the effective radii of the stratospheric aerosol are

very different in SALSA2.0 and M7. While SALSA2.0 was able to reproduce the

observed time evolution of the global burden of sulfate and the effective

radii of stratospheric aerosol, M7 strongly overestimates the removal of

coarse stratospheric particles and thus underestimates the effective radius

of stratospheric aerosol. As the mode widths of M7 have been optimized for

the troposphere and were not designed to represent stratospheric aerosol, the

ability of M7 to simulate the volcano plume was improved by modifying the

mode widths, decreasing the standard deviations of the accumulation and coarse

modes from 1.59 and 2.0, respectively, to 1.2 similar to what was observed

after the Mt. Pinatubo eruption. Overall, SALSA2.0 shows promise in improving

the aerosol description of ECHAM-HAMMOZ and can be further improved by

implementing methods for aerosol processes that are more suitable for the

sectional method, e.g., size-dependent emissions for aerosol species and size-resolved wet deposition.