[CF-metadata] Use of Standard Names and Coordinate Variables(relevant to the aerosol discussion)

From: Christiane Textor <christiane.textor>
Date: Tue, 31 Oct 2006 21:00:30 +0100

Dear all,

Concerning the PM (particulate mass) variables I would like to include
the relative humidity as a coordinate variable and not as part of the
standard_name.

Below I have copied an email from Jean-Philippe Putaud
(jean.putaud at jrc.it) about this issue, that convinced me that this is a
better way to clearly define these variables. In addition, at the US the
most common RH for PM measurements seems to be 30%.

I have changed the PM variables on the wiki page, e.g.:

mass_fraction_of_pm10_aerosol_in_air
The relative humidity should be given as as scalar coordinate variables
using the standard name relative_humidity

But for the optical depth we define e.g.

pm10_ambient_aerosol_optical_depth
The wavelength should be given as as scalar coordinate variables using
the standard name radiation_wavelength

Is it a good idea to define the mass for pm10 at a RH given as
coordinate variable, and the optical depth at ambient RH?

Best regards,
Christiane



> Dear Christiane,
>
> sorry for answering that late (that's due to our email delivery system).
>
> I think that relative humidity has to be specified when reporting PM
> mass concentrations. This has already been well accepted by the
> scientific community when reporting CCN (cloud concensation nuclei)
> number concentrations (actually supersaturation is mentioned in this
> case) or particle hygroscopic growth factor, which are clearly
> functions of RH. The problem with PM mass concentration is quite
> similar.
>
> Most of the pollution monitoring community perform PM mass
> measurements at (close to) 50 % RH. The scientific community has been
> carrying out PM mass measurements at various RHs over the last decade,
> specially at about 20% RH when looking for chemical mass closure.
> Some colleagues are also doing measurements at various RH (ranging
> from very low to very high), like e.g. Regina Hitzenberger in Vienna.
>
> So my suggestion would be to consider RH like a coordinate variable,
> because it can actually be anything, from 10 tp 90%.
>
> Please remember that even measurements reported as "50% RH" are not
> all performed at exactly 50% RH, and that some of the filters most
> commonly used for gravimetric analyses are very hydrophilic (the story
> is even more complicated by the fact that PM mass concentrations
> derive from a double weighing).
>
> Hope this can help.
>
> Regards,
>
> JP
Received on Tue Oct 31 2006 - 13:00:30 GMT