MIRAH - The Isotope gatherer aboard the high altitude research aircraft HALO
Motivation and overview
In recent years, a number of studies have examined the stable carbon isotopic ratios in volatile organic compounds. The kinetic carbon isotope effect for the reaction of VOC with atmospheric oxidants, such as the hydroxyl radical and ozone, has been investigated in different laboratory studies. The interpretation of stable isotopic ratios in atmospheric VOC is supported by the concept of the isotopic hydrocarbon clock, which allows for the estimation of the average photochemical age of components in an air mass. The measurement of stable isotopic ratios is a sensitive tool to investigate the origin of VOC, the atmospheric transformation of the VOC as well as the influence of transport processes on the distribution of VOC and vice versa.
Another application of stable isotopic ratios is the examination of VOC-Budgets in the atmosphere, especially for halogenated VOC. Due to their significant role for stratospheric ozone, the halogenated VOC belong to the most important organic substances in the atmosphere.
The chemistry of the oxidation products of atmospheric VOC is very complex. Studies on isotopic fractionation effects connected with VOC formation and loss reactions and the measurement of their isotopic ratios in the atmosphere help to understand the complex interaction between atmospheric chemistry and secondary organic aerosols as well as the formation of organic particles.
The workgroup of atmospheric physics has therefore developed the air sampler MIRAH (Measurements of Stable Isotope Ratios in Atmospheric Trace Gases on HALO). It is used on various HALO missions. The planned Missions can be found here.
The with MIRAH collected air samples are analyzed in the laboratory by gas chromatography isotope ratio mass spectrometry on stable carbon and hydrogen isotope ratios in VOC. By analyzing the isotopic ratios, “fingerprints” of processes are detected, which influenced individual VOCs. MIRAH is thus an instrument that provides detailed and precise information on dynamics, air mass characteristics and photochemical processing. These are informations that are essential for the interpretation of simultaneous atmospheric measurements.
