Measurements of total odd nitrogen (NOy) aboard MOZAIC in-service aircraft: instrument design, operation and performance
Abstract. A small system for the unattended measurement of total odd nitrogen (NOy, 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 NOy compounds to NO at 300°C on a gold surface in the presence of H2. The instrument has a sensitivity of 0.4-0.7cps/ppt and is designed for unattended operation during 1-2 service cycles of the aircraft (400-800 flight hours). The total weight is 50kg, 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 non-NOy species is <1% for CH3CN and NH3, <5x10-5% for N2O (corresponding to <0.2ppt fake NOy from ambient N2O) and 100% for HCN. The time response of the instrument is <1s (90% change) for NO2. The response for HNO3 is nonlinear: 20s for 67%, 60s for 80%, and 150s for 90% response, respectively.