NILUs Atmospheric Data Base for Interactive Retrieval (NADIR) was set up in 1990 for storing national data on total ozone column levels. The database was substantially expanded when NILU became the data centre for European Arctic Stratospheric Ozone Experiment (EASOE). 

Following EASOE, NADIR also became the data centre for the Second European Stratospheric Experiment (SESAME) and for the Third European Stratospherie Experiment of Ozone (THESEO).

Experimental data from about 60 monitoring stations has been collected in the database. There is data here for a number of parameters like ozone, NO2, and chlorine and bromine compounds, which are relevant to the breakdown of the ozone layer. NILU has put considerable weight on co-ordinating the work of collection, and on the quality control of ozonesonde data. There are several thousand ozonesonde profiles from about 30 stations in Europe and the Arctic during the period 1988 to the present day. Chemical and meteorological data from NADIR is published on CDROM. So far, 5 editions have been produced and 5 new ones are in production.

Common to EMEP, HELCOM, OSPARCOM and AMAP is the monitoring of acid components in air and precipitation, and of trace metals and persistent organic compounds which are particularly harmful to the environment. AMAP additionally contains measurements of climate gases, and EMEP, HELCOM and OSPARCOM are focused on cutrophication as well. EMEP also contains measurements of photochemical active substances. A database has been created which contains measurements and information about samplers, instrumentation and methods. The database is flexible and can store point measurements, which are the most common data types for air and precipitation, measurements along a curve in three dimensions, and area measurements. Today, NILU enters old and new data into the database. The read-in format is the NASA/Ames type. The files in NADIR are also available as flat files in NASA Ames format. NADIR’s software for meteorological data and certain other measurement data is also available through NADIR.

NILU has also the responsibility for the World Meteorological Organisation’s database (WMO/GAW) for surface ozone with data from all over the world.

Potential vorticity is an expression of the extent to which air masses in the Arctic are isolated from air masses farther south.

The higher the potential vorticity, the more isolated the air mass becomes from its surroundings. The temperature drops within the polar vortex during winter and low temperatures allow the ozone to deplete. Furthermore, a strong polar cyclone will also prevent ozonerich air from southern latitudes penetrating into the Arctic during the spring. In March 1997, the polar vortex was substantially more powerful than in March 1992. This provides us with some explanation for the low ozone values in March 1997 compared with the same month five years previously.