An Airborne Study of the Chemistry of Sulfur in the Atmosphere
of the Western North Pacific Ocean
 

Alan R. Bandy and Donald C. Thornton
Chemistry Department
Drexel University
Philadelphia, PA 19104

            During the field phase of TRACE P, our main goal is to determine sulfur dioxide (SO₂) with a frequency of one sample per second and a lower limit of detection of one part per trillion (1 pptv) on the DC-8 aircraft.   A secondary goal is to determine dimethyl sulfide (DMS) with the same frequency and lower limit of detection but only when DMS can play a significant role in sulfur chemistry.  We place DMS in a secondary and nonessential role because our previous studies indicate that the role of DMS in the sulfur chemistry of the atmosphere of the Northwest Pacific is small.

            Our overall goal, however, is to develop a better understanding of the chemistry of sulfur in the atmosphere of the Northwest Pacific.  This is the purpose of the data analysis and interpretative phase of the study to be conducted during the second year.

TRACE P provides us the opportunity to extend our investigations of the chemistry of sulfur in the atmosphere of the western North Pacific that was begun in PEM West A and B^[1].  PEM West A and B were carried out in 1991 and 1994 respectively.  In PEM West A we determined SO₂, DMS, OCS and CS₂ whereas in PEM West B we determined only SO₂ and DMS and often only SO₂ because SO₂ was the dominant sulfur species.  All determinations were made by gas chromatography/mass spectrometry using isotopically labeled internal standards and cryogenic enrichment (GC/MS/ILS)  (Bandy et al., 1992). With this instrumentation a determination of each species was made every 4-6 minutes with a lower limit of detection of about 1 pptv and a precision better than 10% above 20 pptv.  Based on data from PEM West A and B, we participated in the publication of several papers describing the chemistry of sulfur in atmosphere of the western North Pacific (Dibb et al., 1999; Clarke et al., 1998; Newell et al., 1996; Singh et al., 1997; Talbot et al., 1997; Thornton et al., 1996a; Thornton et al., 1996b; Thornton et al., 1997a; Thornton et al., 1997b; Xiao et al., 1997.)

            Although the instrumentation packages flown on PEM West A and B were extensive and sophisticated, they were focused primarily on gas phase photochemistry.  Studies of aerosol were limited to collection and analysis of bulk samples and a condensation nucleus counter that was included on PEM West B to aid in interpreting the (NO)_x data.  There was no information on aerosol size, volatility, etc.  It is this additional focus on aerosol in TRACE P that provides us an opportunity to connect the sulfur chemistry and the aerosol properties at a level of detail that was not possible in PEM West A and B.