So. Farwell et al., AIRBORNE MEASUREMENTS OF TOTAL SULFUR GASES DURING NASA GLOBAL TROPOSPHERIC EXPERIMENT CHEMICAL INSTRUMENTATION TEST AND EVALUATION-3, JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 100(D4), 1995, pp. 7223-7234
A metal foil collection/flash desorption/flame photometric detection (
MFC/FD/FPD) technique was used by investigators from the University of
Idaho (UI) to measure ambient total sulfur gas concentrations from an
aircraft platform during the NASA Global Tropospheric Experiment/Chem
ical Instrumentation Test and Evaluation 3 (GTE/CITE 3) program. The M
FC/FD/FPD technique allowed rapid quantitation of tropospheric backgro
und air masses using sample integration times of 1-3 min with little o
r no gap between measurements. The rapid and continual sampling nature
of this technique yielded data covering approximately 75% of the enti
re CITE 3 program's air track. Ambient air measurement data obtained d
uring northern hemisphere (NH) flights often exhibited relatively high
total sulfur gas values (up to 19 ppb) and an extremely high degree o
f sample heterogeneity, especially in coastal locations. Data from sou
thern hemisphere (SH) flights typically exhibited relatively low total
sulfur gas concentrations and a low degree of sample heterogeneity. A
bimodal interhemispheric total sulfur gas gradient was observed using
data obtained during transit flights between the two CITE 3 program g
round bases. Comparisons were made of UI total sulfur gas measurements
with composite sulfur gas values generated using speciated sulfur gas
measurements from other CITE 3 participants. Only a relatively small
number of overlap periods for comparison were obtained from all the av
ailable CITE 3 data because of large differences in measurement integr
ation times and lack of synchronization of sample start/stop times for
the various investigators. These effects were compounded with extreme
sample heterogeneity in the NH and the speed at which the aircraft tr
aversed the air masses being sampled. Despite these constraints, suffi
cient overlapping data were available for the comparative evaluations.
Comparison of NH UI total with composite sulfur gas values showed exc
ellent correlation and linear curve fit, indicating substantial qualit
ative agreement. Simple linear regression of total on composite sulfur
gas data yielded a slope of 1.9 for coastal NH regions and 1.2 for ma
rine NH regions. The marine NH slope is not statistically different fr
om one, indicating substantial quantitative agreement between UI total
and composite sulfur gas values in these regions. However, a signific
ant difference was observed when these same data were treated with a p
aired t test. SH data exhibited no significant correlation or linear r
egression slope. A paired t test showed a statistically significant di
fference when all SH flights were used. However, data from three SK fl
ights that were classified into a unique group using discriminant anal
ysis showed no significant difference between UI total and composite s
ulfur gas values when analyzed with the paired t test.