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Resonance
Mini
DOAS
I,
II
& III
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(RMDI,
RMDII
&
RMDIII)
Developed by
Resonance Ltd. with Dr. Lois Wardell and
Dr. John Stix of McGill University,
RMDI
employs
the
USB2000
Ocean Optics Spectrometer
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RMDI
is
the
first
of
a series of spectrometers designed to have multi-gas
capabilities. Preliminary tests show excellent response for SO2
and NO2 and future tests scheduled will include other gas species which
will include BrO, OClO, HONO, IO, O3 and
others. Initial testing focused on SO2 and is discussed
below. The data show the use of calibration cells and a
comparison of results from three different wavelengths (310, 312, 315
nm). For more information contact Resonance, Ltd.
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The compact size of the RMDI mounted to
a tripod in comparison to the COSPEC is seen in the figure on the left.
RMDI, using a modified Ocean Optics
USB2000 spectrometer, is powered and operated via USB link to a
laptop/palmtop computer. See Ocean Optics
for specifications on the spectrometer.
Data transfer is also through the USB
link and is collected and displayed real time with an Excel spreadsheet
interface.
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For
comparison
purposes
results
were
calculated using three separate
wavelengths for SO2 (310, 312, and 315 nm) to check for consistency and
optimal results. The figure above and left, shows calibrations
using three different calibration cells (100, 300, 994 ppm-m) with good overlap of the three
wavelengths. The figure above and right, shows the raw output
relative to the calibration cell concentration. Values remain
linear past 1000 ppm-m. The 310 nm
signal has an intercept less than zero illustrating the effect of
overlapping SO2 features in the background sky.
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The
above
left
spectra
of
the gas cell (green) overlapping with the spectra
from the plume (red) indicated a good fit with features over the
presented range of wavelengths. The SO2 absorbance features offer
a number of structural features that correlate the cell to the plume.
Raw
data
from
one
of
the walking traverses is shown above and right.
The beginning and end of the traverse is marked by covering or
“blacking out” the spectrometer. The performance of the three
wavelengths is shown and gives an average peak height of 311 ppm-m.
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Since
no
NO2
was
observed
at Tarumae volcano, a
short test was performed at a coal-fired power plant for this
purpose. A total flux of SO2 = 9.8 Mg/d and NO2 = 0.72 Mg/d were
measured from the power plant stack using RMDI. The instrument
was stationary and manually scanned the sky downwind of the
stack. Wind speed was estimated at 3.2 m/s to calculate the
emission flux. Flux values were calculated similarly to that
described below with the NO2 in the spectral range of 411 to 415 nm.
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Development
of
RMDI
and
additional
multi-gas spectrometers is ongoing. The
photo at the left shows atmospheric background studies near 0 Latitude,
0 Longitude at the Galapagos Islands.
A
volcanic
multi-gas
field
study is planned for spring 2004 at Mt. Etna
and will include at least
three different spectrometer prototypes.
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The
project
is
headed
by
Drs. John Stix
(right) and Bill Morrow (left) and is assisted by post-doctorate
researcher, Dr. Lois Wardell (below right).
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Part
of
the
development
includes
comparisons to COSPEC, the standard for SO2
remote sensing of volcanic gas emissions. Resonance Ltd., is the only supplier of COSPEC.
The
photo
to
the
right
shows RMDI and COSPEC being used for an
undergraduate senior thesis looking at industrial pollution sources.
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The
long
term
relationship
between
Resonance Ltd. and McGill's Department
of Earth & Planetary Sciences supports development of innovative
ideas and research in volcanic gas monitoring as well as excellent
educational opportunities.
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Undergraduate
field
assistant,
Abby
Peterson,
conducts SO2 measurements at a smelter
in Sudbury, Ontario by scanning beneath the
plume during SUDS2004.
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SUDS2004
was
a
collaborative
effort
with Environment Canada. Combining
RMDI SO2 scans with a LIDAR which measures aerosol density, we were
able to study the gas transport behavior of the smelter emissions.
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