Measurement of Selected Reactive Nitrogen and Oxygenated Species: Description of the PANAK Instrument System

H. B. Singh, NASA Ames Research Center, Moffett Field, CA 94035

The PANAK (PAN-Aldehydes-Ketones) instrument package is a fully computerized airborne three channel Gas Chromatographic system designed for the collection and analysis of low-ppt levels of PANs, alkyl nitrates, tertrachloroethene, C₂-C₃ aldehydes, C₁-C₂ alcohols, and C₃-C₄ ketones.  The instrument can be expanded to measure higher homologues of oxygenates as well as acetonitrile and hydrogen cyanide. The system consists of computer controlled instrument functions for sample drying, collection, and processing as well as data collection.  Pressure variations on the instrument system during flight are minimized by use of absolute valves to maintain a constant pressure.  The PANAK system constantly draws five liters/min sample air through a heated Teflon lined probe and manifold from which each of the three instrument channels draws a 200ml aliquot of sample air. The air sample is then cooled cryogenically to -140 ˚C in a trap for pre concentration of its constituents.  In the case of the oxygenate channe,l most of the sample moisture is removed by passing the flow through a –35 ˚C degree cold trap before pre concentration.  After pre concentration the traps are switched in line with the gas chromatographic columns and desorbed for component separation and detection.  The PAN channels use short packed Carbowax columns with ECD detectors, while the oxygenate channel uses DB wax capillary columns with a Photo Ionization Detector placed in series with a Reduction Gas Detector.  All calibrations are performed in-flight by using an installed dilution system and in a manner that mimics ambient air sampling.  Primary standards are generally referred to a series of permeation tubes.  In addition high concentration standards are also carried on board.  Sensitivities under typical conditions are: PANs-1-3 ppt, alkyl nitrates-1-5 ppt, acetone-5 ppt, other oxygenates-15 ppt.  Accuracies of the order of ±25% are expected.  A schematic of this instrument is provided below.