Abstract Information on scattering coefficients, size distributions and chemical composition of the Arctic aerosol, obtained from NILU aircraft measurements, has shed light on the origins of polluted air layers in the Arctic air. Very long-range, episodic transport of air masses, over several thousand kilometers, clearly affects the quality of the Arctic air, both during the Arctic summer and winter seasons. Polluted air masses, carrying a mixture of anthropogenic air pollutants from a variety of sources in different geographical areas, have been identified in the Arctic atmosphere over Svalbard at altitudes from 2.0 km to 4–5 km. The altitude of polluted air layers is higher in winter than in summer. The layers of polluted air at altitudes below 2.5 km can be traced to episodic transport of air masses from sources situated in areas with air temperatures similar to those in the Norwegian Arctic. During the BP Project aircraft measurement campaigns, the relevant sources were located exclusively in northern U.S.S.R. The long-range transport of air pollutants over northern U.S.S.R. to the Norwegian Arctic is the dominating feature in the winter half of the year, but a lesser one in the summer half. Both anthropogenic and natural pollutants from local sources may contribute to the layers of contaminated air up to altitudes of ca 1000 m, particularly during summertime.