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. 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.
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