The CAMS European air quality forecast can be retrieved from the Atmosphere Data Store (ADS) in either GRIB or NetCDF format. When requesting multiple models and/or variables in GRIB format however, it may not be clear which fields are which. The model that a field belongs to is identified by its "centre" and "subCentre" keys, and the variable by its "parameterNumber" and "constituentType" keys.

The tables below show the mapping. Below that is some example Python code showing how this information can be used with ecCodes to identify the model and variable of each field in a GRIB file.

ModelcentresubCentre
CHIMERE85200
DEHM85203
EMEP880
Ensemble median852
EURAD-IM85201
GEM-AQ85204
LOTOS-EUROS990
MATCH8298
MOCAGE851
SILAM860
MINNI85205
MONARCH85206
VariableparameterNumberconstituentType
Alder pollen5962100
Ammonia09
Birch pollen5962101
Carbon monoxide04
Dust062001
Formaldehyde07
Glyoxal010038
Grass pollen5962300
Mugwort pollen5962201
Nitrogen dioxide05
Nitrogen monoxide011
Non-methane VOCs060013
Olive pollen5964002
Ozone00
Particulate matter < 10um (PM10)040008
Particulate matter < 2.5um (PM2.5)040009
Peroxyacyl nitrates (PANs)060018
PM2.5, total organic matter only062010
PM10, sea salt (dry) only062008
PM10, wildfires only062096
Ragweed pollen5962200
Residential elementary carbon062094
Secondary inorganic aerosol (SIA)062099
Sulphur dioxide08
Total elementary carbon062095
from eccodes import (
    codes_grib_new_from_file, codes_get, codes_release, codes_write)

# Dictionary matching ADS API key/value pairs to grib key/value pairs
definitions = {
    'variable': {
        'ammonia': {
            'parameterNumber': 0,   # Mass density (kg/m3)
            'constituentType': 9},
        'carbon_monoxide': {
            'parameterNumber': 0,
            'constituentType': 4},
        'dust': {
            'parameterNumber': 0,
            'constituentType': 62001},
        'formaldehyde': {
            'parameterNumber': 0,
            'constituentType': 7},
        'glyoxal': {
            'parameterNumber': 0,
            'constituentType': 10038}, 
        'non_methane_vocs': {
            'parameterNumber': 0,
            'constituentType': 60013},
        'nitrogen_monoxide': {
            'parameterNumber': 0,
            'constituentType': 11},
        'nitrogen_dioxide': {
            'parameterNumber': 0,
            'constituentType': 5},
        'ozone': {
            'parameterNumber': 0,
            'constituentType': 0},
        'peroxyacyl_nitrates': {
            'parameterNumber': 0,
            'constituentType': 60018},
        'particulate_matter_10um': {
            'parameterNumber': 0,
            'constituentType': 40008},
        'particulate_matter_2.5um': {
            'parameterNumber': 0,
            'constituentType': 40009},
        'pm2.5_anthropogenic_wood_burning_carbon': {
            'parameterNumber': 0,
            'constituentType': 62098},
        'pm2.5_anthropogenic_fossil_fuel_carbon': {
            'parameterNumber': 0,
            'constituentType': 62097},
	    'pm2.5_total_organic_matter': {
            'parameterNumber': 0,
            'constituentType': 62010},
        'pm10_sea_salt_dry': {
            'parameterNumber': 0,
            'constituentType': 62008},
        'pm10_wildfires': {
            'parameterNumber': 0,
            'constituentType': 62096},
        'residential_elementary_carbon': {
            'parameterNumber': 0,
            'constituentType': 62094},
        'secondary_inorganic_aerosol': {
            'parameterNumber': 0,
            'constituentType': 62099},
        'sulphur_dioxide': {
            'parameterNumber': 0,
            'constituentType': 8},
        'total_elementary_carbon': {
            'parameterNumber': 0,
            'constituentType': 62095},
        'alder_pollen': {
            'parameterNumber': 59,     # Number Concentration (1/m3)
            'constituentType': 62100},
        'birch_pollen': {
            'parameterNumber': 59,
            'constituentType': 62101},
        'grass_pollen': {
            'parameterNumber': 59,
            'constituentType': 62300},
        'mugwort_pollen': {
            'parameterNumber': 59,
            'constituentType': 62201},
        'olive_pollen': {
            'parameterNumber': 59,
            'constituentType': 64002},
        'ragweed_pollen': {
            'parameterNumber': 59,
            'constituentType': 62200}
    },
    'model': {
        'chimere': {
            'centre': 85,      # France
            'subCentre': 200},
        'dehm': {
            'centre': 85,
            'subCentre': 203},
        'emep': {
            'centre': 88,      # Oslo
            'subCentre': 0},
        'ensemble': {
            'centre': 85,      # France
            'subCentre': 2},
        'euradim': {
            'centre': 85,      # France
            'subCentre': 201},
        'gemaq': {
            'centre': 85,
            'subCentre': 204},
        'lotos': {
            'centre': 99,
            'subCentre': 0},
        'match': {
            'centre': 82,      # Norrkoping
            'subCentre': 98},
        'mocage': {
            'centre': 85,      # Meteo France
            'subCentre': 1},
        'silam': {
            'centre': 86,      # Helsinki
            'subCentre': 0},
        'minni': {
            'centre': 85,
            'subCentre': 205},
        'monarch': {
            'centre': 85,
            'subCentre': 206}
    }
}


def identify_field(msg):
    """Return a dict identifying the input grib message"""

    field = {}
    for api_key, value_to_grib in definitions.items():
        for api_value, grib_defn in value_to_grib.items():

            # Does this message match the key/value pairs in grib_defn?
            match = True
            for grib_key, grib_value in grib_defn.items():
                msg_value = codes_get(msg, grib_key,
                                      ktype=type(grib_value))
                if msg_value != grib_value:
                    match = False
                    break
            if match:
                field[api_key] = api_value

        if api_key not in field:
            raise Exception('Unrecognised field')

    return field


def main(grib_file, output_filename_template=None):
    """Read all fields in the GRIB file, identify the model and variable of
       each, and optionally write them to output files, split by model or
       variable or both.

       Any instance of "<model>" or "<variable>" in output_filename_template
       will be replaced by the associated model or variable string for the
       field, e.g. output_filename_template='<model>.<variable>.grib'
    """

    fields_written = {}

    # Loop over messages in a grib file, identifying all fields
    count = 0
    with open(grib_file) as fin:
        while True:
            msg = codes_grib_new_from_file(fin)
            if msg is None:
                break
            count += 1

            try:
                field = identify_field(msg)
                print('Field ' + str(count) + ' is: ' + repr(field))

                # Write the field to an output file?
                if output_filename_template:
                    name = output_filename_template
                    for k, v in field.items():
                        name = name.replace(f'<{k}>', v)
                    if name not in fields_written:
                        fields_written[name] = 0
                        mode = 'w'
                    else:
                        mode = 'a'
                    with open(name, mode + 'b') as fout:
                        codes_write(msg, fout)
                    fields_written[name] += 1

            finally:
                codes_release(msg)

    for name, n in fields_written.items():
        print(f'Wrote {n} fields to {name}')


if __name__ == '__main__':
    main('mydata.grib',
         output_filename_template='<model>.<variable>.grib')