This was a study of the effect of the placing of different types of air filters on the air-quality of the storage rooms of the Government Archives in the Hague. Here there were in the different rooms different types of air filters in the air-filtering system. Concentrations of NO, NO2, ozone and SO2 were measured throughout tow or three 24 hour period, as well as the outside air by the central entrance point of the air handling system as in the storage rooms locations. Nearby some formaldehyde and ammonia was produced. A considerable amount of NO2 and ozone was taken up in the air-conditioning system. SO2 was present throughout and given off by the system. All types of Purafil cooling filters capturing ozone and a large amount of NO2 removed about 80%. The Chmisorbant was a strong oxidizer, oxidizing a large quantity of the reduced gas NO and formaldehyde (for SO2 it was not dependable). This type led to the production of more oxidation. For NO which was oxidized to NO2 a low quantity of NO2 came out of these filters. The application of an oxidizing filter as in the Purafil Chemisorbant was deemed at least debatable.