INTRODUCTION
INSTRUMENTATION
SCOPE
United States
Environmental Protection
Agency
Environmental Monitoring
Systems Laboratory
P.O. Box 93478
Las Vegas NV 89193-3478
August 1990
OFFICE OF RESEARCH AND DEVELOPMENT
TECHNOLOGY SUPPORT PROJECT
Open Path FT-IR Use in
Environmental Monitoring
A major environmental
concern is the identification,
location, and extent of volatile
organic compound (VOC)
contamination in the air at
hazardous waste sites. Open
path (or long path) FT-IR was
adapted to environmental use
to address the need for
information about VOC levels
and to improve upon costlier
and more time-consuming
current methods. Open path
FT-IR is useful at many
stages of screening and
remediation because VOC
contamination can result from
many sources, including
underground storage tank
leaks, chemical spills, and off-
gassing at air stripping plants.
A mobile system has been
developed at Kansas State
University through a coopera-
tive agreement with EMSL-LV
and Region 7. The mobile
laboratory set-up provides an
on-site, quick turnaround
means of obtaining data that
can guide remediation deci-
sions. The outlook for ex-
panded use of open path
FT-IR is excellent, with re-
search in the area responding
to the needs of field scientists
and Agency personnel.
The FT-IR spectrometer
being used for developmental
work is a Bomem DAO2
system equipped with a KBr/
Ge beam splitter, a mercury-
cadmium-telluride detector
that is liquid nitrogen cooled,
an adjustable tripod, and a
collection telescope (10-inch
Cassegrainian). The source
is an air cooled and quartz
shielded Nernst glower
operating at 2,000 Kelvin.
This source is located at the
focal point of a 20-inch
Newtonian telescope in order
to generate a colli mated
beam of infrared radiation.
The mobile laboratory is
driven to one side of the site
to be surveyed and the FT-IR
spectrometer with its collec-
tion telescope is set up
adjacent to the station. The
IR source and its collimating
telescope are positioned on
the opposite side of the site
to be surveyed so that the
collimated beam of infrared
radiation may be sent across
to the collection telescope of
the FT-IR spectrometer. A
laboratory calibration is
usually sufficient for field
sampling.
An alternative arrangement is
to place both the source and
the spectrometer adjacent to
the laboratory station. Then a
reflector is placed on the
opposite side of the site so
the collimated beam of
infrared radiation is sent
across the site to the reflector
and bounced back to the
spectrometer. In either
arrangement, the IR absorp-
tion spectrum of the atmo-
sphere above the site is used
to identify any VOC present in
the path of the beam.
Open path FT-IR is useful for
the qualitative and quantita-
tive measurement of VOC
and low-boiling semivolatile
compounds. To date, the
spectral database contains
35 VOC files, with a total of
70 compounds expected to
be included by the end of
1990. The instruments can
be positioned at varying
heights above the soil by
using tripods. Though this
technology is sensitive to
meteorological factors such
as wind, paniculate matter,
and rain, most of these
affect point sampling by
canister as well. Open path
FT-IR is faster and cheaper
than the canister methods
while providing a greater
likelihood of locating the
pollutant plume and should be
the favored technique when
time and budgetary con-
straints are considerations.
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ADVANTAGES AND
LIMITATIONS
FUTURE PLANS
Using open path Ft-IR to
analyse the atmospheric
concentration of VOC and
solvents is a 'newly developed
and-erjitfrflinp; technology, it
has many advantages and
limitations fhat are
here as an aid to
Computerized operation
Rapid results 8*^ to mett«ft>IOQical changes
PiQvMa$ aWajK(DPflMfflation along pathway
meihodot^Qy decistofMnaking.
(ft
that the:Data
(DQO)ofa
s(t» must driy.e the decisions '
on instrumentation so thatthe
necessary data ar? not
compromised. Aawfthany
equipment and expert advice
is fundamental to the site-
specific applicability of the
technique.
As open path FT-IR gatng,
stature a£an; environmental
screening too), work wiH be
underway to refine its capa-
bilities in quantitation. A
growing database that will.
include more VOC and-some
semivolatile compounds will
increase tha usefulness of
this method. The.
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