Dear all,
I am currently reviewing a set of variables from two major data hubs with
air quality data, and the objective is to enable those systems to serve
netcdf-CF data. Looking through their variables and descriptions, I came across
a couple of things and I would like to initiate the discussion about these now.
I group the following into three categories: 1) errors/inconsistencies in the
current CF standard_name table, 2) request for additional standard_names
following the accepted grammar rules, 3) other issues and questions potentially
requiring new grammar rules or further discussion. As always your feedback is
greatly appreciated.
Best regards,
Martin
1. standard_name table errors/inconsistencies:
* "mole_fraction_of_nox_expressed_as_nitrogen_in_air"
The distinction "expressed_as_nitrogen" doesn't make sense for the
"mole_fraction" quantity. The mole fraction basically counts the number of
molecules and normalized this quantitiy with respect to the number of air
molecules. Hence, you can simply add the mole fraction of NO and the mole
fraction of NO2 to arrive at the mole fraction of NOx. This is different for
the mass_fraction, where you need to express this relative to a given molar
mass. Thus, "mass_fraction_of_nox_expressed_as_nitrogen_in_air" makes perfect
sense, but "mole_fraction_of_nox_expressed_as_nitrogen_in_air" should be
changed into "mole_fraction_of_nox_in_air" and the present standard_name should
be deprecated. [I recall that there was some discussion about this earlier, but
I don't know how this ever made it into the table]
* The same issue applies to
"mole_fraction_of_nox_expressed_as_nitrogen_in_air", "
mole_fraction_of_clox_expressed_as_chlorine_in_air",
" mole_fraction_of_nmvoc_expressed_as_carbon_in_air" and potentially other
"group" names.
* " mass_fraction_of_alkanes_in_air" (and other "group" names)
Here we face the opposite problem: mass fraction requires an agreement on
the "reference mass", so here it should be added "..._expressed_as_carbon_..."
* Definition of the phrase: "expressed_as"
Current wording:
The phrase 'expressed_as' is used in the construction A_expressed_as_B, whereB
is a chemical constituent of A. It means that the quantity indicated by the
standard name is calculated solely with respect to the B contained in A,
neglecting all other chemical constituents of A.
Suggested improvement:
Change last half-sentence to " neglecting all other elemental constituents of
A."
Actually, this may be more complicated, because in the air quality world it is
also common to express things relative to one molecule. Example:
"nox_expressed_as_nitrogen_dioxide". In this case the phrase " calculated
solely with respect to the B contained in A" does not really make sense, as
"NO2" is not "contained in NO" (which is part of NOx, however).
2. request for new standard names following the accepted grammar rules
* " mass_concentration_of_pm2p5_ambient_aerosol_in_air", units "kg m-3"
Definition: Mass concentration means mass per unit volume and is used in the
construction mass_concentration_of_X_in_Y, where X is a material constituent of
Y. A chemical species denoted by X may be described by a single term such as
'nitrogen' or a phrase such as 'nox_expressed_as_nitrogen'. "Aerosol" means the
suspended liquid or solid particles in air (except cloud droplets). "Ambient
aerosol" is aerosol that has taken up ambient water through hygroscopic growth.
The extent of hygroscopic growth depends on the relative humidity and the
composition of the aerosol. "Pm2p5 aerosol" is an air pollutant with an
aerodynamic diameter of less than or equal to 2.5 micrometers. To specify the
relative humidity and temperature at which the particle size applies, provide
scalar coordinate variables with the standard names of, respectively,
"relative_humidity" and "air_temperature".
* " mass_concentration_of_pm1_ambient_aerosol_in_air", units "kg m-3"
Definition: Mass concentration means mass per unit volume and is used in the
construction mass_concentration_of_X_in_Y, where X is a material constituent of
Y. A chemical species denoted by X may be described by a single term such as
'nitrogen' or a phrase such as 'nox_expressed_as_nitrogen'. "Aerosol" means the
suspended liquid or solid particles in air (except cloud droplets). "Ambient
aerosol" is aerosol that has taken up ambient water through hygroscopic growth.
The extent of hygroscopic growth depends on the relative humidity and the
composition of the aerosol. "Pm1 aerosol" is an air pollutant with an
aerodynamic diameter of less than or equal to 1 micrometer. To specify the
relative humidity and temperature at which the particle size applies, provide
scalar coordinate variables with the standard names of, respectively,
"relative_humidity" and "air_temperature".
[Note that pm1 actually coincides with the current definition of "coarse_mode"
- it may be helpful to allow both terms as aliases]
* " mass_concentration_of_pm10_ambient_aerosol_in_air", units "kg m-3"
Definition: Mass concentration means mass per unit volume and is used in the
construction mass_concentration_of_X_in_Y, where X is a material constituent of
Y. A chemical species denoted by X may be described by a single term such as
'nitrogen' or a phrase such as 'nox_expressed_as_nitrogen'. "Aerosol" means the
suspended liquid or solid particles in air (except cloud droplets). "Ambient
aerosol" is aerosol that has taken up ambient water through hygroscopic growth.
The extent of hygroscopic growth depends on the relative humidity and the
composition of the aerosol. "Pm10 aerosol" is an air pollutant with an
aerodynamic diameter of less than or equal to 10 micrometers. To specify the
relative humidity and temperature at which the particle size applies, provide
scalar coordinate variables with the standard names of, respectively,
"relative_humidity" and "air_temperature".
* "mole_fraction_of_hydrogen_sulfite_in_air", units "1" (meaning "mole mole-1")
Definition: Mole fraction is used in the construction mole_fraction_of_X_in_Y,
where X is a material constituent of Y. Hydrogen sulfide is the molecule with
the chemical formula H2S.
* "mole_fraction_of_alkanes_in_air", units "1" (meaning "mole mole-1")
Definition: Mole fraction is used in the construction mole_fraction_of_X_in_Y,
where X is a material constituent of Y. Alkanes are saturated hydrocarbons,
i.e. they do not contain any chemical double bonds. Alkanes contain only
hydrogen and carbon combined in the general proportions C(n)H(2n+2); "alkanes"
is the term used in standard names to describe the group of chemical species
having this common structure that are represented within a given model. The
list of individual species that are included in a quantity having a group
chemical standard name can vary between models. Where possible, the data
variable should be accompanied by a complete description of the species
represented, for example, by using a comment attribute. Standard names exist
for some individual alkane species, e.g., methane and ethane.
* " mass_concentration_of_coarse_mode_ambient_aerosol_in_air", units "kg m-3"
Definition: Mass concentration means mass per unit volume and is used in the
construction mass_concentration_of_X_in_Y, where X is a material constituent of
Y. A chemical species denoted by X may be described by a single term such as
'nitrogen' or a phrase such as 'nox_expressed_as_nitrogen'. "Aerosol" means the
suspended liquid or solid particles in air (except cloud droplets). "Ambient
aerosol" is aerosol that has taken up ambient water through hygroscopic growth.
The extent of hygroscopic growth depends on the relative humidity and the
composition of the aerosol. Coarse mode aerosol is aerosol having a diameter of
more than 1 micrometer.
* "mole_fraction_of_aldehydes_in_air", units "1" (meaning "mole mole-1")
Definition: Mole fraction is used in the construction mole_fraction_of_X_in_Y,
where X is a material constituent of Y. Aldehydes are organic compounds with a
CHO group; "aldehydes" is the term used in standard names to describe the group
of chemical species having this common structure that are represented within a
given model. The list of individual species that are included in a quantity
having a group chemical standard name can vary between models. Where possible,
the data variable should be accompanied by a complete description of the
species represented, for example, by using a comment attribute. Standard names
exist for formaldehyde as the simplest member of the aldehydes group.
* " mole_fraction_of_dichlorine_in_air", units "1" (meaning "mole mole-1")
Definition: Mole fraction is used in the construction mole_fraction_of_X_in_Y,
where X is a material constituent of Y. Dichlorine is the molecular form of
elemental chlorine with the chemical formula Cl2.
* "mole_fraction_of_methlyglyoxal_in_air", units "1" (meaning "mole mole-1")
Definition: Mole fraction is used in the construction mole_fraction_of_X_in_Y,
where X is a material constituent of Y. Methylglyoxal is an organic molecule
with the chemical formula CH3COCHO. It is also called pyruvaldehyde or
2-oxopropanal.
3. Other issues and questions:
* (actually more a question): How do I express the "daily 8 hour maximum" value
that is derived from hourly measurements of (surface) ozone mole fractions? I
would tend to apply cell_methods here, but how should this attribute look like?
To explain in more detail: first an 8-hour running mean of hourly
concentrations is calculated, then the daily maximum value of these running
means is picked as the indicator.
* How can we get more specific about the "extinction coefficient"? In
particular, we would like to express something like
"..._due_to_Mie_scattering". But does this work with "
volume_extinction_coefficient_in_air_due_to_ambient_aerosol". The new name
would then become
"volume_extinction_coefficient_in_air_due_to_Mie_scattering_of_ambient_aerosol"
? (and would "Mie" be spelled with "M" or "m"?)
* In one of the lists I am reviewing, a new lumped group "acetic acid and
higher carboxylic acids" appears. Am I right that one should simplify this to
"mole_fraction_of_carboxylic_acids_in_air" and express in the definition that
this group contains acetic acid and higher carboxylic acids?
* Stumbling over the "group" or "lumping" concept again, I would propose to add
a new attribute to the CF standard which is specifically used to describe the
group compounds. This should be an optional attribute (which means that the
general rule " Where possible, the data variable should be accompanied by a
complete description of the species represented..." remains the same), yet by
separating it from the generic comment attribute, one would allow for more
intelligent metadata processing. Two suggestions for such an attribute name
would be
"group_constituents" or "group_members"
The former is more specific and bears some relation to composition in its name,
the latter would be more generic and could potentially be used in other areas
as well (for example to denote plant species in a definition of plant
functional types, soil types belonging to one group, etc.).
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