Construction and testing of an in-situ No/Noy measuring system aboard the high-altitude research aircraft M55-geophysica

The fully automated in-situ measuring system SIOUX (Stratospheric Observation Unit for nitrogen oXides) has been developed and established under flight conditions. SIOUX is a two channel measuring device designed for the high-attitude research aircraft M55-Geophysica to record reactive nitrogen oxides in the upper troposphere and the lower stratosphere. Channel A detects nitric oxide (NO) and channel B the total reactive nitrogen (NOy), which is reduced to NO on the surface of a heated gold-converter in conjunction with carbon monoxide (CO) as reducing agent. The technique used for the measurement of NO is chemiluminescence. The detection limit of channel A is 6 pmol/mol and of channel B 10 pmol/mol for an Integration time of 1 s. The main components of SIOUX are the sample inlet, the detector incorporating the reaction chambers, photomultlpliers and ozone generators, the converter, a pumping system, a calibration/operation gas system and the data recording unit. Except for the sample inlet all components are housed in a pressurised aluminium container. This has a length of 1.1 m, a diameter of 0.6 m and a total mass of 250 kg; the maximum power consumption of SIOUX is 1300 W. For aeronautical compliance four test procedures were required to guarantee the flight compatibility of the mechanics and electronics of the device: shock/vibration/EMC (ElectroMagnetic CompatlbilltyVpressure test. In October 2001 SIOUX was implemented for the first time aboard the M55-Gsophysica during a test campaign In Russia. There, the measuring system was monitored under flight conditions and its operation was established for stratospheric conditions. Mixing ratios for NO and NO were registered up to an attitude of 20 km. In July 2002 SIOUX was used aboard the M55-Geophysica for validation the ENVISAT instrument MIPAS-E in Italy. A comparison was made tor the first time between MIPAS-E measurements of nitric acid (HNO3) and SIOUX measurements of NOy-NOx ( HNO3 in the altitude range 17-20 km). A mean deviation of 20%±6 % between the MIPAS-E and the SIOUX data was registered.