Our understanding of tropospheric chemistry is limited primarily by our ability to accurately measure the minute quantities of key tropospheric species. An initial, and continuing, focus of the GTE has been the development, testing, and evaluation of techniques capable of airborne measurements of trace species. A series of rigorous airborne intercomparisons, called the Chemical Instrumentation Test and Evaluation (CITE) experiments have been conducted to evaluate the performance of promising instrumentation. These intercomparisons were conducted blind and under conditions which expose the instruments to a wide range of conditions in both polluted and clean -air settings. The advanced instruments validated by CITE have been used to carry out GTE field measurements in regions of critical importance to global tropospheric chemistry.
Three CITE mission have been conducted as part of GTE. The CITE-1 mission, consisting of a ground- based intercomparison (1983), and two separate airborne campaigns (1983 and 1984), evaluated instrumentation for measuring carbon monoxide (CO), nitric oxide (NO), and the hydroxyl radical (OH). The CITE- 2 mission focused on intercomparison of techniques for measuring nitrogen dioxide (NO2), nitric acid (HNO3) and peroxyacetylnitrate (PAN), as well as a re-evaluation of NO techniques. The CITE-3 mission focused on intercomparison of techniques to measure key sulfate species sulfur dioxide (SO2), dimethylsulfide (DMS), hydrogen sulfide (H2S), carbonyl sulfide (COS), and carbon disulfide (CS2).