Information about air constituents is vital for providing knowledgeable answers to current environmental research issues. In addition to the „classic” greenhouse gases such as CO2, CH4, CO and H2O which have been and which continue to be at the centre of attention with regard to global change, ever more constituents of the air are gaining significance in atmospheric research. Here it is apparent that real time measurements in the field detect trends more quickly from which forecasts can be derived. To guarantee this, robust but compact measuring systems are required which can detect the concentrations and isotope ratios for the most important molecules up to an accuracy of ppb. Modern equipment with a high temporal resolution in terms of measurement frequencies in the hertz range are deployed in the most diverse atmospheric „flux” measurements. Measurements with these modern devices are, of course, not restricted to the field; they can also be used under indoor conditions at any time.