NOAA ship Discoverer
Nonmethane Hydrocarbon Data set -- EQUILIRATOR  MEASUREMENTS
Preliminary data set measured, reduced and compiled by MIT
VERSION 4.0, MAY 14, 1997
Ron Prinn, Gary Kleiman, Alex Pszenny, Ashwini Deshpande, and Xian Shi


Data File CODIAC_EQU contains the following parameters:

Julian Time
Julian Date
propane
2-me-propane
butane
2-me-propene
c-2-butene
cyclopentane
2-me-butane
pentane
1,3-butadiene


Julian Time
The Julian Time is listed in the format YDDDHHMM where the Y represents
the 5 in 1995, DDD is the day of year, HH is the hour of the day and MM the 
minute of that hour all listed in GMT. The time listed corrsponds to the 
start of sample collection, thus 52971521 would be the representation
for a sample which was collected starting at 3:21 PM GMT on October 24, 1995.
(Some sample collections took up to 20 minutes.) 

Julian Date
The Julian day of year listed in decimal days (GMT). Thus 297.640 would also 
be the representation for 3:21 PM GMT on October 24, 1995.

propane
2-me-propane
butane
2-me-propene
c-2-butene
cyclopentane
2-me-butane
pentane
1,3-butadiene
All compounds listed here are reported in parts per trillion by volume as
observed in air equilibrated with surface seawater on the ship. Detection 
limits are between 6 and 14 ppt for all of the compounds listed, thus for this 
data file, all but the last digit are significant.

1. Instrument and Operation

Measurements were obtained by cryogenically preconcentrating between 300 and
500 ml of gas drawn through stainless steel tubing from the headspace of an
onboard equilibrator. Samples were dried with phosphorous pentoxide (Aquasorb) 
traps and sodium hydroxide (Ascarite) traps were used to remove carbon dioxide. 
The concentrated samples were then analyzed with a Hewlett-Packard 5890 Series 
II gas chromatograph with a PLOT (Chrompack) column and flame ionization 
detector.

2. Calibration and Data Reduction

Calibrations were achieved by measuring an on-board gas standard (prepared
at MIT and intercalibrated through the IGAC/NOMHICE activity) nominally
once per day. Linearity of the FID is assumed and concentrations are calculated
based on integrated area under corresponding peaks of the chromatogram.
Due to potential saturation of traps with hydrocarbons from the standard gas,
each chromatogram immediately following a standard collection, and 4
chromatograms following a trap change have been excluded. Other measurements
were rejected when a clear analytical problem was noted (e.g. collection
flow rate was not maintained, damage to column discovered, etc.)

While the data set remains preliminary and subject to change as analysis
proceeds, generally good agreement is found between many of the data and
those obtained previously by Donahue and Prinn (JGR 98, No. D9, Pg. 16,915,
1993) during the 1990 SAGA III cruise and Shi and Prinn (JGR, submitted)
during the 1992 MAGE cruise.