Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 4 5 2004 10.5194/acpd-4-6149-2004 http://www.atmos-chem-phys-discuss.net/4/6149/2004/ http://www.atmos-chem-phys-discuss.net/4/6149/2004/acpd-4-6149-2004.html http://www.atmos-chem-phys-discuss.net/4/6149/2004/acpd-4-6149-2004.pdf 6149 6183 2004-10-05 Measurements of total odd nitrogen (NO_y) aboard MOZAIC in-service aircraft: instrument design, operation and performance A. Volz-Thomas a.volz-thomas@fz-juelich.de M. Berg T. Heil N. Houben A. Lerner W. Petrick D. Raak H.-W. Pätz Institut für Chemie und Dynamik der Geosphäre II: Troposphäre, Forschungszentrum Jülich, Jülich, Germany A small system for the unattended measurement of total odd nitrogen (NO_y, i.e., the sum of NO and its atmospheric oxidation products) aboard civil in-service aircraft in the framework of MOZAIC is described. The instrument employs the detection of NO by its chemiluminescence with O₃ in combination with catalytic conversion of the other NO_y compounds to NO at 300°C on a gold surface in the presence of H₂. The instrument has a sensitivity of 0.4–7 cps/ppt and is designed for unattended operation during 1–2 service cycles of the aircraft (400–800 flight hours). The total weight is 50 kg, including calibration system, compressed gases, mounting, and safety measures. The layout and inlet configuration are governed by requirements due to the certification for passenger aircraft. Laboratory tests are described regarding the conversion efficiency for NO₂ and HNO₃ (both >98%). Interference by HCN and NH₃ is 100% and <1%, respectively. The time response (90% time) of the instrument is <1 s for NO₂ and 150 s for HNO₃, the latter being caused by memory effects in the 80 cm long inlet line.