Modern methods of the measurement of atmospheric trace gases Invited Lecture

Measurements of trace gas concentrations and other quantities are a crucial tool for the investigation of the processes in the atmosphere. At the same time the determination of atmospheric trace gas concentrations constitutes a technological challenge, since extreme sensitivity (some species have to be detected at mixing ratios as low as 10-13) is desired simultaneously with high specificity, i.e. the molecule of interest usually must be detected in the presence of a large excess of other species. To date no single measurement technique can, even nearly, fulfil the above and other requirements for trace gas measurements in the atmosphere. Therefore a comprehensive arsenal of techniques has been developed. Besides a large number of special techniques (like the chemiluminescence-detection of NO) universal methods gain interest, due to their relative simplicity—a single instrument can register a large number of trace species. The different types of requirements and the various techniques are discussed, special emphasis is given to spectroscopic methods, which are a successful and promising variety, that plays a large and growing role in atmospheric chemistry research. For instance only spectroscopic methods allow remote sensing of trace gas concentrations, e.g. from satellite platforms. Today many varieties of spectroscopic methods are in use (e.g. tunable diode laser spectroscopy or Fourier transform spectroscopy), the basic properties and recent applications of this technique are presented by the example of differential optical absorption spectroscopy (DOAS). Future requirements and expected developments are discussed.