Geophysical Observatory of the Institute of Geophysics Polish Academy of Sciences, Otwock-Swider, Poland
The Geophysical 0bservatory at Swider is located 25 km South-Southeast of the capital, Warsaw, and 2.5 km North-Northwest of the Otwock town, a small resort and local administrative center (population 20, 000). The bounded premises of the Observatory, some 7 ha (0.7 km3) of the surface area, are overgrown by pine and deciduous trees with a few clearings.
Mean aerosol concentration 3 nm - 3 mm (last 5 years) -10,000 particles cm-3.
Ground radioactivity - very low.
Number of 24-hour long fair-weather days per year - 30% (mainly May-Sep).