Hi Martin,
Lots of good suggestions. My thoughts are interleaved below.
Philip
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Dr Philip Cameron-Smith, pjc at llnl.gov, Lawrence Livermore National Lab.
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> -----Original Message-----
> From: cf-metadata-bounces at cgd.ucar.edu [mailto:cf-metadata-
> bounces at cgd.ucar.edu] On Behalf Of Schultz, Martin
> Sent: Monday, October 03, 2011 11:30 AM
> To: cf-metadata at cgd.ucar.edu
> Subject: [CF-metadata] Standard_name table entries for air quality data
>
> 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.
[PJC] For some species it doesn't make any difference, as you point out, but for others it can, such as N2O5 expressed as nitrogen, and there are dichlorine oxides. I can imagine some people might want to have all of their variables using '_expressed_as_' to avoid the need for consistency and for users to need to understand the point you make. These names aren't wrong (at worst they are duplicative), and somebody must have wanted them in the first place, so I favor letting them stay.
> * " 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_..."
[PJC] I expect some observations could generate mass_fraction_of_alkanes_in_air without knowing the speciation. Models can also worked with lumped species without necessarily knowing the speciation. The speciation could also be different between different measurements so two measurements with the same carbon could have different mass. That said, it is likely that many people will want to be able to use _expressed_as_carbon_ too.
>
>
> * 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).
>
[PJC] Point well made. Fortunately it is usually clear enough in practice :-).
>
> 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.
[PJC] After a quick read these all look good to me :-).
> 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.
[PJC] I don't have an answer, I just want to reinforce the usefulness of having such cell_methods. 1-hour means are also common.
> * 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"?)
[PJC] I couldn't find any precedent in the std_name list, but this would seem sensible and generally consistent with existing grammar.
[PJC] I couldn't find any capital letter in the std_name list, but I also couldn't find any proper nouns (such as people's names) either.
> * 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?
[PJC] Is the issue that you want to exclude formic acid? Long ago we had discussions about including nomenclature such as C2 and C2+ to designate carbon numbers per molecule in groups. I don't think they were ever used in the end. If we want to revive the idea, then we could have something like mole_fraction_of_C2+_carboxylic_acids_in_air (are symbols allowed in std_names?)
> * 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.).
[PJC] Both seem reasonable to me. It should be acknowledged that the constituents list should be able to contain specific species and further lumped groups, eg 'acetic acid and higher carboxylic acids'.
>
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Received on Mon Oct 03 2011 - 13:43:44 BST
