MEASUREMENTS AND CHEMISTRY OF SELECTED REACTIVE NITROGEN AND OXYGENATED SPECIES OVER THE TROPICAL PACIFIC OCEAN

(PEM-TROPICS-B)

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

We aim to deploy on the DC-8 aircraft, a three channel instrument package in its PAN/Aldehyde/Ketone (PANAK) configuration.  Air flows through a heated Teflon lined manifold at a rate of 5 liter per minute (0˚C and 1 atm.).  A sample of 200 ml is drawn from the manifold and cryogenically collected at –140˚C in several sampling loops.  In one of the channel measuring oxygenates a cold trap (-35˚C) is inserted in the sampling line to remove excess moisture.  The cryogenically preconcentrated air sample is simultaneously heated and injected into the measuring system.  All calibrations, are performed inflight 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.  In this configuration, PAN (Peroxyacetyl nitrate), PPN (Peroxypropionyl nitrate), tetrachloroethylene (tracer of urban air), and select alkyl nitrates (methyl, ethyl, and i-propyl nitrates) are separated on two EC-GC channels allowing a measurement every 4 to 5 minutes to a sensitivity of 1 ppt or better.  The third channel equipped with a coupled Reduction Gas detector and a Photoionization detector (PID) uses capillary chromatography and is currently focused on the measurement of select oxygenated compounds especially carbonyls and alcohols.  Exploratory efforts are also underway to detect and measure ambient levels of CH₃CN and HCN using the existing PANAK configuration.  These are excellent tracers of biomass burning emissions and have not been previously measured.  Their atmospheric fate and role is largely unknown.  We plan to prepare, integrate and test the PANAK instrument aboard the DC-8, and participate in the PEM-Tropics-B deployment (March.-April, 1999) to perform measurements of PAN, PPN, methyl nitrate, ethyl/i-propyl nitrates, tetrachloroethylene, acetone, methylethyl ketone, methanol, ethanol, acetaldehyde, propanal, CH₃CN and HCN to low ppt levels.  We also plan to validate, process and analyze all data collected during PEM-Tropics, and interpret these to ascertain sources and chemistry of oxygenated hydrocarbons, reactive nitrogen species, atmospheric free radicals, and ozone.