United States
Environmental Protection
Agency
Atmospheric Research and
Exposure Assessment Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S3-89/036 Aug. 1989
v>EFA Project Summary
Evaluation of a FTIR Mobile
Source Measurement System
John E. Sigsby Jr., Alex McArver, and Richard Snow
An Initial evaluation was made of a
prototype Fourier transform infrared
spectrometer on its ability to mea-
sure mobile source emissions. This
prototype represents the commer-
cialization of Research Technology
developed by the Ford Motor Co. The
system utilizes a Mattson Instruments
Co. interferometer coupled to a Mass-
comp computer. The required soft-
ware is still incomplete. This has re-
sulted In the inability to correct
errors or optimize results. Unrelia-
bility of both hardware and software
has been a major shortcoming of this
system. When operating properly, the
system measures carbon dioxide,
nitric oxide, and formaldehyde accur-
ately, both when compared to bag
analysis and on direct point-by-point
comparisons with real-time data.
Carbon monoxide is measured low,
whereas methanol is about 35 %
high. Real-time analysis appears to
be available for a variety of other
compounds such as ammonia, hydro-
gen cyanide, nitrous acid, nitrous
oxide, formic acid, a number of
Individual hydrocarbons, etc. Com-
pletion of the evaluation awaits the
final software translations and im-
provements in reliability.
This Project Summary was devel-
oped by EPA's Atmospheric Research
and Exposure Assessment Laboratory,
Research Triangle Park, NC, to an-
nounce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering Information at
back).
Introduction
There is a need for improved analysis
of organic species that may be emitted
from mobile sources. Ideally such meas-
urements would include analysis already
made and be flexible enough to add addi-
tional measurements in the future. Fourier
transform infrared spectroscopy (FTIR)
has shown the potential for providing
such analysis.
Two groups have demonstrated the
direct application of this technique to the
problem, (I) Nicolet in conjunction with
Volkswagen and (2) Ford Motor Co. Ford
has licensed their technology to Mattson
Instruments for use on their brand of
FTIR instruments. The Ford system was
better developed and had superior char-
acteristics in selectivity and limits of
detection. The Nicolet system uses a
more classical approach. The Ford sys-
tem uses multiple wavelengths, and ma-
trix deconvolution by subtractive proce-
dures. Because this approach uses multi-
ple wavelengths, it should be more spe-
cific. This approach has the limitation in
that the multiple wavelengths used may
overlap those used by other compounds.
The choice of an absorption band within
its linear range of response is important.
The combination of wavelengths chosen
are called masks. A compound that has a
wide range of concentrations in various
situations will have multiple masks, each
with a different set of wavelengths and
their corresponding absorption coef-
ficients.
The Office of Mobile Sources, Office of
Air and Radiation of the US EPA has
become very interested in this technol-
ogy to solve or reduce several analytical
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problems associated with the use of
alternate fuels. Of particular interest is the
analysis of formaldehyde and methanol.
Ford Motor Co. has also sought to have
the technique recognized as an approved
alternative to the classical analytical pro-
cedures.
In addition, the FT1R technique has
potential in the research and charac-
terization of mobile source emissions. It
can quantitate components not normally
sought and, if the spectra is known,
identify new components not previously
identified. This can be accomplished in
real time, as the emissions are occurring.
This allows the evaluation of emission
control systems and their temporal
effects, (when do they start/stop working,
etc.), as has been demonstrated by Ford
Motor Co.
To perform this evaluation, NSI was
authorized to procure an appropriate
system.
This system as received in April 1988
was very incomplete. Ford had initially
developed the system on a spectrometer
that it had built which utilized a DEC POP
11/40 computer to process the data.
They subsequently purchased a regular
Mattson Instruments spectrometer and
adapted some of the software to it. They
have since received a unit identical to
ours but generally use the older systems.
When Mattson Instruments began to
use the Ford software on their equipment
they found that their normal computer
was too small. A Masscomp Computer
was used that had far superior speed and
central processing unit capabilities. The
memory and bulk storage capacity of the
unit we received has been shown to be
still too small. A software problem
occurred when Masscomp updated its
operating system, which is a version of
UNIX. Such updates occur fairly fre-
quently and the new versions are often
not upwardly compatible. Such updates
must be installed because Masscomp
can not guarantee to deliver another unit
capable of operating on the old operating
system. This problem will continue until
Mattson Instruments can supply further
orders for the specific computer. This has
necessitated two rewrites of the software.
The FTIR was expected to analyze the
regulated mobile source emissions as
well as a wide variety of other emissions.
These measurements were expected to
be made in real-time and in the batch
mode on bags. Initially the unit we
received could not perform real-time
analysis or even continuous analysis for a
short period of time. During this period
we were only able to exercise the instru-
ment on calibration and similar tests.
Unfortunately continual problems with the
spectrometer have resulted in a very
poor service record. These problems
appear to be related to the basic
spectrometer.
After the updated software was
received at the end of September we
were able to start a reasonable evaluation
program. This program has been in-
hibited by software limitations, largely
because software has not yet been trans-
lated. This problem is addressed in the
full report.
Initial evaluation of the FTIR system in
relation to analytical results from simul-
taneously collected bag samples showed
that the system, as configured, correctly
analyzed carbon dioxide, nitric oxide, and
formaldehyde. Carbon monoxide appear-
ed to be about 10 % low. This discrep-
ancy probably occurred because the best
mask range could not be used. This
mask contained an error in its con-
struction and the software that allows cre-
ation and editing of masks has not yet
been translated. Methanol results were 35
% high. The analytical signal was noisy.
These problems may also be mask
related.
The FTIR system was compared with
our other analytical techniques on a real-
time basis. The results were fully com-
patible with those described above. With
this technique, comparison can be made
of the emission rates of individual com-
pounds and concurrent measurements
such as catalyst temperature. Many
emissions such as formaldehyde have a
reasonable noise level between 0.1 and
0.2 PPM. It was possible the follow the
emissions of nitrous oxide, ammonia,
methane, ethylene and propylene. The
hydrocarbons agreed well with concur-
rent gas chromatographic analysis of
bags. Acetylene was measured at about
half the level measured by the GC,
whereas consistently high values for eth-
ane and 1,3-butadiene were reported by
the FTIR.
Other compounds sought but not seen
in significant concentrations included ni-
trogen dioxide, nitrous acid, hydrogen
cyanide and formic acid. Most of these
compounds had acceptable noise levels
in the very low PPM range.
Conclusions
The system appears to have a large
potential for utilization in both routine
emissions measurements, where it could
replace several instruments currently
used, and in research evaluations of fuels
and vehicle emissions. The ability to
adapt the basic routine instrument to
analyze additional compounds that mig
be required due to changes in technoloj
is very attractive. This would require or
a change in the mask set utilized, r
change or addition of instrumentatk
would be required. This potential must I
further explored.
The research potential of the system
large. The emission rate of individu
components may be followed ar
evaluated. This capability requires on
that they have a reasonably intense ar
specific infrared spectra.
The system evaluated is a prototyf
system that is still incomplete. It is nc
apparent that a larger hard drive and
larger mass storage system are nece
sary for the archival storage of tr
spectra for future evaluation.
Hardware reliability is a major issu
The system rarely operates for more th*
a few weeks at a time without tr
necessity of service. The problems whic
appear to be in the spectrometer ai
inexplicable because the basic hardwai
is the same as that in the top of lir
version of the Mattson Instruments con
mercial system. According to Mattson di
ferences between our system and th
commercial system are in the computi
and its peripherals.
Software deficiencies fall into sever
categories and each have their ow
priority.
Software reliability must be improve
to a point where the system will operal
properly when started.
The software is not currently us«
friendly, which would be required f(
routine application by non-spectroscof
ists.
It is highly desirable that the system b
operable in the multi-user mode.
It is also desirable that data display an
processing be allowed during dat
acquisition.
The ability to create, edit, and modil
masks is a requirement for a workin
system. This ability is currently availabl
only through the Ford Motor Co. and th
use of their initial system.
The system has no graphics capability
It would be desirable to be able to pl<
spectra on the screen and to manipulal
these spectra. Currently, spectra ar
created, stored, translated and can the
be transmitted for- external hardcop
plotting. Spectral subtraction is the onl
function available for spectral manipi
lation. This function is extremely awkwar
and time-consuming to use because c
the external plotting requirement, whic
requires that, for each subtractive iterz
tion, the resultant spectra be createc
translated, transferred and a hard cop
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plot created. Baseline correction and
smoothing are examples of common
spectral tasks that can not be performed.
Such functions are highly desirable if
optimal utilization is to be made of the
unit.
The default mask set should be
changeable. With its current default mask
set, the system comes up ready to test
cars operating on ethanol. This mask set
must be changed each time the system
is started.
Multiple masks are required for
compounds which are present over a
wide range of concentrations. The
system can now use only one mask per
run. If the concentration of an individual
component varies over a wide range,
reprocessing the data with multiple
masks and selecting the "appropriate"
data from each data set are required. An
"automatic span" selection of the
appropriate mask is highly desirable.
The system does not reprocess data
automatically. If an FTP is to be
reprocessed with a separate mask set,
each scan must be recalled individually,
more than 600 scans for the three bags
of the Federal Test Procedure. This is not
practical and should be changed before
the system is finalized.
The restrictions to 512 scans and the
3 s per scan are inhibiting.
The current system is restricted to real-
time analysis by the software available.
This is very limiting.
Recommendations for Future
Work
These recommendations assume that
the appropriate software and hardware
modifications to make this a practical
working system will be made within a
reasonable period of time. Because the
effort is considerably larger than appar-
ently had been envisioned by Mattson
Instruments and Ford, a maximum effort
to cooperate and encourage completion
of this work should be continued.
The current evaluation is incomplete.
As the software/hardware is updated each
change must be evaluated for efficacy
and reliability.
The currently available masks, that
have not yet been evaluated, should be
tested for specificity, noise level, limits of
detection, and linear range.
The analog inputs recently
incorporated into software must be
checked and evaluated.
A "Mini-dilution System" is part of the
total FTIR System. This Mini-dilution
tunnel allows a more concentrated signal
to be seen by the FTIR with a concurrent
lowering of the limits of detection. This
addition should be evaluated.
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The EPA author,John E Sigsby, Jr., (also the EPA Project Officer ,see below), is
with the Atmospheric Research and Exposure Assessment Laboratory, Research
Triangle Park, NC 27711; Alex McArver and Richard Snow are with NSI
Environmental Sciences, Research Triangle Park, NC 27709.
The complete report, entitled "Evaluation of a FTIR Mobile Source Measurement
System," (Order No. PB 89-180 822/AS; Cost: $13.95, subject to change) will be
available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Atmospheric Research and Exposure Assessment Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States Center for Environmental Research
Environmental Protection Information
Agency Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S3-89/036
000085833 PS
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