PMEL DMS System
NOAA Ship Discoverer
ACE-1 Methods:

Air and seawater were immediately analyzed aboard ship for DMS concentrations using the same 
automated collection/purge and trap system.  Air samples were collected through a Teflon line 
which ran approximately 60 m from the top of the aerosol sampling mast (17 m above sea level, 
forward of the ship’s bridge) to the analytical system.  One hundred ml/min of the 4 L/min flow 
were pulled through a KI solution at the analytical system to eliminate oxidant interferences 
(Saltzman and Cooper, 1989).  The air sample volume ranged from  0.5 to 1.5 L depending on 
the DMS concentration.  Seawater samples were collected from the ship's seawater pumping 
system at a depth of approximately 5 m.  The seawater line ran to the analytical system where 
5.1 ml of sample were valved into a Teflon gas stripper.  The samples were purged with 
hydrogen at 80 ml/min for 5 min.  Water vapor in either the air or purged seawater sample stream 
was removed by passing the flow through a -25C Teflon tube filled with silanized glass wool.  
DMS was then trapped in a  -25C Teflon tube filled with Tenax.  During the sample trapping 
period, 6.2 pmole of methylethyl sulfide were valved into the hyrogen stream as in internal 
standard.  At the end of the sampling/purge period the coolant was pushed away from the trap 
and the trap was electrically heated.  DMS was desorbed onto a DB-1 mega-bore fused silica 
column where the sulfur compounds were separated isothermally at 50C and quantified with a 
sulfur chemiluminesence detector. The detection limit during ACE-1 was approximately 0.8 
pmole.  The system was calibrated using gravimetrically calibrated permeation tubes.  The 
precision of the analysis, based on both replicate analyses of a single water sample and replicate 
analyses of a standard introduced at the inlet of the air sample line, was typically +- 8%.  The 
performance of the system was monitored regularly by running blanks and standards through the 
entire system.  Values reported here have been corrected for recovery losses.  System blanks 
were below detection limit.  Air samples are reported in units of nmol/m3 at standard temperature 
(25C)and pressure (101.3 kPa) such that 1 nmole/m3 equals 24.5 ppt.  The flux of DMS from the 
ocean to the atmosphere in micromoles/square meter/day was calculated using the exchange 
coefficients of Wanninkhof, 1992 and Liss and Merlivat, 1986.