Klaus Pfeilsticker, (Co-I of P2),Prof. Dr., has been involved with many aspects of the environmental physic research over the past 23 years. He actively took part in numerous international measurement campaigns (CHEOPS 3, EASOE, SESAME, THESEO, SOLVE, VINTERSOL, SCOUT-O3, SCIAVAL, SHARP etc.) aimed at the investigation of the Earth’s ozone layer, the deposition of the solar radiation in the atmosphere, and the isotopic composition of the atmosphere and hydrosphere. In recent years, he has been actively developing the balloon-borne UV/visible solar occultation technique, UV/visible limb measurements from high-altitude balloons and aircrafts, and the high-resolution oxygen A-band spectrometry. Major applications of the employed techniques are the chemistry of tropospheric and stratospheric ozone, and the radiative transfer of the atmosphere. To date he has authored or contributed to 95 peer-reviewed publications in international journals and he contributed to the WMO assessment reports on stratospheric ozone in 2002, 2006 and 2010 and the 2nd Assessment report on European research in the stratosphere.