[CF-metadata] aerosol water

[Jonathan Gregory]

Dear Christiane

> >>>>mass_fraction_of_water_in_ambient_aerosol_in_air

> > OK, I see there could be a distinction between in_air and in_cloudy_air.
> and in_clouds or in_snow etc...

> > If aerosol particles are in cloud water or in precipitation, are they 
> still "ambient" aerosol? Do they still have a meaningful mass fraction 
> of water?
> 
> This distinction would not make sense anymore. It could be dry or 
> ambient aerosol in air, or aerosol at a certain rel. humidity in air. Or 
> they could be contained another phase like clouds or precip, but not at 
> the same time in air.

As a result of all this, I understand that you need
  mass_fraction_of_water_in_ambient_aerosol_in_air
where "ambient" distinguishes it from a specified RH. Thanks for explaining
that. But if the aerosol is dry or in another phase, I don't think it is
ambient, so you would not include "ambient". Anyway, we will perhaps discuss
this again if/when such names are definitely proposed. :-)

Best wishes

Jonathan