During 1983-2001, NASA conducted a collection of field campaigns as a part of the Global Tropospheric Experiment (GTE) to develop advanced instrumentation to measure critical atmospheric trace gases and quantify their sources, sinks, and distribution. Among those were the Chemical Instrumentation Test and Evaluation (CITE) missions, which had the overarching goal to test and evaluate the instruments developed for the GTE missions. To accomplish this objective, the CITE missions adopted the methodology of conducting intercomparisons of airborne measurements obtained for the same species by instruments utilizing fundamentally different detection principles (Hoell et al., 1990). The second phase of the CITE missions, CITE 2, was the first systematic evaluation of both instrumentation and photochemistry of odd nitrogen from an airborne platform (Hoell et al., 1990). Odd nitrogen is a crucial component of tropospheric chemistry. The common understanding of odd nitrogen chemistry at the time of GTE had come into question as being incomplete. Hoell et al. (1990) state that ground-based measurements showed there may be significant unidentified members of the NOy family and that “simple” odd nitrogen chemistry may not be fully understood, driving the objectives of CITE 2. CITE 2 was conducted in August 1986 with a focus on daytime odd nitrogen and the evaluation of instrumentation developed for measuring nitrogen species, specifically nitrogen dioxide (NO2), nitric acid (HNO3), and peroxyacetyl nitrate (PAN). Additional questions related to the abundance and partitioning among members of the odd nitrogen family were studied (Hoell et al., 1990).

To accomplish its objectives, the CITE 2 team deployed the NASA Lockheed Electra aircraft equipped with a suite of instrumentation for the intercomparison of nitrogen species augmented with ancillary measurements such as temperature, dew point, wind velocity, aircraft position, CO, and ozone (O3). Ancillary measurements were added to the payload to answer questions related to tropospheric odd nitrogen budgets and photochemistry. Along with the airborne measurements, the CITE 2 campaign also relied on a ground-based evaluation of calibration standards for HNO3, NO2, PAN, and intercomparison of airborne ambient measurements of each species. Based at Moffett Field, California, CITE 2 took place over a four-week period conducting measurements over California and the eastern Pacific Ocean. While CITE 1 and CITE 2 used identical measurement techniques for NO2, the campaigns used different measurements techniques for the remaining species. Detailed descriptions related to the motivation, implementation, and instrument payloads are available in the CITE 2 overview paper. A collection of the publications based on CITE 2 observations are available in the Journal of Geophysical Research special issue: Global Tropospheric Experiment/Chemical Instrumentation Test & Evaluation.