Measurements of total odd nitrogen (NO y ) aboard MOZAIC in-service aircraft: instrument design, operation and performance

A small system for the unattended measurement of total odd nitrogen (NOy, i.e., the sum of NO and its at- mospheric oxidation products) aboard civil in-service air- craft in the framework of MOZAIC is described. The in- strument employs the detection of NO by its chemilumines- cence with O3 in combination with catalytic conversion of the other NOy compounds to NO at 300 C on a gold surface in the presence of H2. The instrument has a sensitivity of 0.4-0.7 cps/ppt and is designed for unattended operation dur- ing 1-2 service cycles of the aircraft (400-800 flight hours). The total weight is 50 kg, including calibration system, com- pressed 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 NO 2 and HNO3 (both >98%). Interference by non-NOy species is <1% for CH3CN and NH3, <5◊10 5 % for N2O (cor- responding to <0.2 ppt fake NOy from ambient N2O) and 100% for HCN. The time response of the instrument is <1 s (90% change) for NO2. The response for HNO3 is nonlin- ear: 20 s for 67%, 60 s for 80%, and 150 s for 90% response, respectively.