Folks,
A few thoughts here:
As Ute made reference, some of us in the oil spill modeling community have
had previous discussions about netcdf standards for oil spills information
-- in that case, mostly model results, but there is a lot of overlap with
field measurements as well.
So I suggest that as a community we address the whole pile, rather than
adding a single new standard name.
I offer up this gitHub repo as a central point for discussion:
https://github.com/NOAA-ORR-ERD/nc_particles
or we could make a new one for standard names if we like.
In the meantime:
I would like to propose to use a standard name like
> "mass_fraction_of_contaminant_in_sea_water"
>
This is a fine idea -- to have _something_ that covers a lot of use cases
in the meantime. exactly what the contaminant is, and how it was measured
can be in the long name or other meta-data.
Roy wrote:
> There is a parameter 'total petroleum hydrocarbons' (TPH) defined as 'A
> mixture comprising all substances comprising totally of carbon and hydrogen
> that may be extracted from a sample using an organic solvent. These are
> presumed sourced from crude oil.'.
having one for TPH is a fine idea as well -- this is a very commonly used
convention. The "presumed sourced from cure oil" is a bit odd, but I
suppose, correct, if "sourced" in interpreted broadly :-)
I also mention that in my experience of these measurements contamination of
> water samples is reported in units of micrograms per litre, i.e. mass
> concentration rather than mass fraction.
yeah, this is a convention that has always bugged me -- as far as I can
tell, everyone considers the two equivalent -- i.e. one milligram per liter
IS one part per million, and they are used interchangeably. I personally
call this "concentration in water", and assume 1kg/liter for the water) --
I don't know that there is a way to express that equivalence in CF or
udunits, so I would suggest that the "official" unit be mass fraction --
it's more precise and clearly defined.
>
> I agree that petroleum_hydrocarbons is more specific and therefore
> preferable.
> Is it possible to omit "total", or does it have a specific meaning too and
> therefore convey some extra information?
I've always seen "total" in there, usually to distinguish from more
specific measurements that capture particular classes of compounds, like
PAHs. As "TPH" is in really common use, I suggest we keep it.
https://www3.epa.gov/region1/eco/uep/tph.html
Having read through the SeaOWL specification provided by Mike's link, I see
> it is something totally new making a combination of fluorescence and
> backscatter measurements at different wavelengths and using the results
> in a calibration algorithm to produce measurements of an analyte that
> WETLabs/SeaBird describe as 'crude oil'. This is NOT the same thing as TPH
> (a wet chemical measurement), although in most environments the two will
> be linearly correlated. I therefore now think that it would be best to
> use the terminology of the instrument manufacturer: i.e. 'crude_oil'.
The use of fluorescence to measure oil in water is fraught with difficulty,
and lacking in precision -- it looks like WETLabs has done an admirable job
(speaking only from their literature, and a VERY limited understanding of
the science) of developing a tool for that purpose (rather than simply
using a CDOM tool and expecting it to work), but I seriously doubt that
they can distinguish between "crude oil" and petroleum-derived hydrocarbons
in general. And I doubt they'd even want to.
For instance, if a refined product is spilled, that is not crude oil, but
it is PH, and I'm sure their instrument would measure it.
Also, as Ute pointed out, once released into the environment, crude oil
weathers and changes, so it's no longer "crude" strictly speaking.
I suspect the term "crude oil" is being used for marketing, and "TPH" is
what they are really trying to measure. I'm sure what they are really
trying to do is make the point that their instrument measures hydrocarbons
(maybe petroleum derived, rather than other sources of fluorescence.
I can run this by folks in our group that understand all this better than
I, if there is still uncertainty
--
Christopher Barker, Ph.D.
Oceanographer
Emergency Response Division
NOAA/NOS/OR&R (206) 526-6959 voice
7600 Sand Point Way NE (206) 526-6329 fax
Seattle, WA 98115 (206) 526-6317 main reception
Chris.Barker at noaa.gov
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