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

From: Raymond M. Hoff <hoff>
Date: Tue, 31 Oct 2006 15:54:03 -0500 (EST)

I am loath to wade in on the middle of an argument as a newbie but how can
you define optical depth (a column measurement through the atmosphere) at
a single RH? That does not make sense. An in-situ measurement at a given
RH has some meaning but not for column values.

Ray

-- 
Raymond M. Hoff
Professor of Physics
Director, Joint Center for Earth Systems Technology (JCET)
Director, Goddard Earth Science and Technology Center (GEST)
University of Maryland, Baltimore County
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Baltimore MD 21228
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Christiane Textor wrote:
> 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
>
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Received on Tue Oct 31 2006 - 13:54:03 GMT