mean_nox_emissions_10km_year1990 has been replaced by mean_nox_emissions_10km_year2000 in the ontology

In the ontology, the field mean_nox_emissions_10km_year1990 is described,
but we do not use such a field in the database.
The field, that is used in the database is labeled mean_nox_emissions_10km_year2000.