[CF-metadata] CF: surface flux versus emissions

From: Schultz, Martin <m.schultz>
Date: Wed, 12 Nov 2008 02:15:26 +0100

Dear all, and Jonathan in particular,

    here is a short view on my understanding of the distinction between
surface flux and emission:

1) surface flux can go both ways, i.e. a negative surface flux can mean
effective deposition of a species (whereas people generally don't talk
about negative emissions)

2) technically, a surface flux is often implemented as a boundary
condition in the vertical diffusion routine

3) inasmuch as emissions are treated as surface fluxes, number 2) holds
for emissions as well, but there are other ways of treating emissions,
such as simply adding the respective mass per timestep to the
concentration or distributing the accumulated mass over certain vertical
levels

4) semantically, one can argue that all emissions are fluxes in the
sense that they are given in units of mass per area and time

5) an attempt to define the term emissions would be "release of a
species from one compartment into another given as mass per unit area
(or volume if you prefer) and time". This broad definition avoids a
characterisation of the actual source process which may be difficult

6) even if emissions are distributed vertically, they are often given as
a surface flux combined with a vertical profile that specifies the
fraction of these emissions to be placed in each vertical layer.
Therefore there is some right to label most emissions as surface fluxes
even in such cases. However, this doesn't work for aircraft emissions or
lightning NOx. The latter may or may not be called "emissions", because
it is actually a chemical process within the atmosphere...

Sorry: I don't think this makes matters much clearer.

Best regards,

Martin


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Dr. Sebastian M. Schmidt
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Received on Tue Nov 11 2008 - 18:15:26 GMT