Air Mass Factor using a Chemistry Transport Model
There are two approaches taken to convert the SO2 slant column density,
retrieved with a DOAS technique, into a vertical column density. Both
approaches use an Air-Mass Factor (AMF). This page describes the use of a
chemistry transport model to obtain this air mass factor.
In this approach the retrieval of the VCD for SO2 will be based on a
combined retrieval/modelling approach, similar to the approach for some
other trace gases (such as formaldehyde, HCHO). The main motivation for this
new approach is to improve the accuracy of the retrieval. A
chemistry-transport model (TM4 for example), driven by high-quality meteorological
fields from ECMWF, will provide best-guess profiles of SO2, based on the
latest emission inventories, atmospheric transport, photochemistry and
wet/dry removal processes.
These model forecast fields will be collocated with the satellite (GOME-2,
SCIAMACHY, OMI) observations, and the radiative transfer modelling in the
retrieval will be performed based on the model trace gas profile and
temperature profiles. The retrieval is coupled to cloud top height and cloud
fraction retrievals derived from the satellite data, and the retrieval will
be coupled to high quality albedo maps.
This approach is currently not under evaluation.
Possibly it will be picked up again at a later stage.