Regular ground-based measurements of characteristics of atmospheric gas composition have been acquired at St. Petersburg State University (59 degrees 88' N, 29 degrees 83' E) since 1991. Equipment and techniques for interpreting the ground-based observations using measurements of spectra of direct solar IR radiation, zenith scattered UV and visible radiation are described. Main attention is centered on long-term variations of different trace gases, results of complex measurements of different atmospheric gases (O-3, CO2, N2O, NO2, HF, HCl, HNO3 etc.) by Fourier spectrometer Bruker, comparisons of various ground-based methods for measuring the total columns of trace gases and the validation of different satellite measurements of total columns of trace gases.