NASA - National Aeronautics and Space Administration

The Ames PANAK instrument is a computerized 3- channel Capillary Gas Chromatographic system designed for the collection and analysis of low ppt (10-12 v/v) levels of peroxyacyl nitrates (PANs), alkyl nitrates, and tertrachloroethene in Channels 1 and 2; and C2-C3 aldehydes, C1-C2 alcohols, C3-C4 ketones, and C1-C2 nitriles in channel 3. Channels 1 and 2 use ECD detectors and have a sampling frequency of 2.5 minutes. Channel 3 uses a Photo Ionization detector placed in series with a Reduction Gas detector and has a sampling frequency of 5 minutes. The main manifold draws 5 SL/min of ambient air through a heated Teflon lined probe from which each of the three instrument channels draws a 200 ml aliquot of sample air. This aliquot is dried by passing it through a –35 °C cold trap, cooled to -140 °C for constituent pre concentration, and then heat desorbed into the gas chromatographic columns. 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: 1-3 ppt PANs, 1-5 ppt alkyl nitrates, 5-20 ppt OVOC, and 20-30 ppt nitriles.

The PAN-CIGAR chemical ionization mass spectrometer which measures up to 7 PAN species simultaneously and semi-continuously with a time resolution of ~2 seconds. The method is based on the detection of the acylperoxy radicals formed from thermal decomposition of the PAN species at the inlet by reacting them with iodide ions, which are formed by passing methyl iodide diluted in nitrogen through an α–particle source. The reaction of the peroxy acyl radicals with I- forms IO and the acyl ion, which is detected using a quadrupole mass spectrometer (Extrel) at a mass to charge ratio of 59 in the case of PAN. The method is very specific for PAN type compounds and the limit of detection is ~1 pptv/s or better for most PAN species. The instrument employs a realtime continuous calibration using isotopically labeled PAN produced in-situ by a photolytic calibration source.