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.
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