Title: Discoverer NMHC Data - Water

Contact:

   Ronald Prinn
   MIT
   Department of Meteorology
   77 Massachusetts Ave. Rm 54-1312
   Cambridge, MA, USA, 02139
   Telephone: (617) 253-2452
   Facsimile: (617) 253-0354
   E-Mail Address: rprinn@mit.edu


Data Set Description:

NOAA ship Discoverer
Nonmethane Hydrocarbon Data set -- EQUILIRATOR  MEASUREMENTS
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 contains the following parameters:

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 UTC. The time listed corresponds to the
start of sample collection, thus 52971521 would be the representation
for a sample which was collected starting at 3:21 PM UTC on October 24, 1995.
(Some sample collections took up to 20 minutes.)

Julian Date
The Julian day of year listed in decimal days (UTC). Thus 297.640 would also
be the representation for 3:21 PM UTC 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 pre-concentrating between 300 and
500 ml of gas drawn through stainless steel tubing from the head space 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.)

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.

Format: space-delimited ASCII.

Date (YYYY/MM/DD) (UTC)
Time (HH:MM:SS) (UTC)
Julian Decimal Date (UTC)
propane (pptv)
2-me-propane (pptv)
butane (pptv)
2-me-propene (pptv)
c-2-butene (pptv)
cyclopentane (pptv)
2-me-butane (pptv)
pentane (pptv)
1,3-butadiene (pptv)


File Name Conventions:
   nmhc_wat.dat


References:
 Donahue and Prinn (JGR 98, No. D9, Pg. 16,915, 1993)
 Shi and Prinn (JGR, submitted)