United States
Environmental Protection
Agency
Atmospheric Sciences Research
Laboratory
Research Triangle Park NC 27711
,,
Research and Development
EPA/600/S3-88/040 Dec. 1988
&EPA Project Summary
Investigation of Analyzer
Problems in the Measurement of
NOX from Methanol Vehicles
Peter A. Gabele
The rapid development of vehicles
designed to operate on methanol fuel
has prompted development and
evaluation of methods for measuring
their emissions. Classical measurei
ment methods prescribed for
gasoline cars are not always
applicable to methanol cars because
of the inherently high concentrations
of methanol and formaldehyde in
their emissions. One such exception
applies to the FID (flame ionization
detector) measurement of hydro-
carbons in the presence of methanol.
Another less publicized exception
and the subject of this report
pertains to the chemiluminescent
method of measuring nitrogen oxides
(NOX) from methanol cars.
The chemiluminescent method is
based upon the principle that nitric
oxide (NO) can be reacted with
ozone (03) to give about 10 percent
electronically excited NO2*. When the
electronically excited NO2* transits to
its normal state, a detectable light
emission is given off. The intensity of
this emission is directly proportional
to the mass flow rate of NO into the
reaction chamber. The light
emission is detected and measured
by a photomultiplier tube and the
associated electronics process a
voltage response which is
proportional to the intensity of light
being emitted. To make this method
applicable to NOX (NO + NOg)
emissions, the NC>2 in the sample is
changed to NO in an NOa converter.
Problems with chemiluminescent
NOX measurement from methanol
cars were first reported as large
variations in NOX data and large
values of NO2- Later descriptions
identified a sort of residual response
which occurred immediately
following sample analysis while the
analyzer was being zeroed. These
symptoms tried but found to be
impractical because of resultant
zero/span difficulties. The
interference was finally cleared by
cleaning the analyzer's reaction
chamber. Isolation of the reaction
chamber as the source of
contamination was attained by
systematically exchanging parts
between the old and new analyzers
until the interference went away.
NOX measurements were made on
tailpipe emissions from a Methanol
Escort with the older Beckman 951A
before and after its reaction chamber
was cleaned. The measurements
were compared with those from a
TECO chemiluminescent NOx
analyzer which had demonstrated no
response to either methanol or
formaldehyde. Before cleaning, the
Beckman measurement was about 35
percent higher than the
measurement from the TECO. After
cleaning, the difference between
measurements was reduced to about
3 percent.
Toward the conclusion of the
study, the new Beckman 95IA began
responding to formaldehyde. A
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response between 4 and 7 ppm was
obtained with a 100 ppm
formaldehyde sample. No response
to methanol occurred. It is estimated
that this first observed response to
formaldehyde occurred after
subjecting the new analyzer to three
or four 60 liter bags of 100 ppm
formaldehyde and two or three bags
of 250 ppm methanol.
This Project Summary was devel-
oped by EPA's Atmospheric Sciences
Research Laboratory, Research
Triangle Park, NC, to announce 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).
Conclusions and
Recommendations
A study was carried out to investigate
the extent and source of irregularities
related to the measurement of NOX
emissions from methanol cars.
Corrective measures were also explored.
Because the results in this study were
obtained in tests using Beckman 951A
Chemiluminescent Analyzers, some of
the conclusions based on those results
are relative to the experience with that
particular analyzer. However, there is
evidence which suggests that other types
of Chemiluminescent analyzers could be
similarly affected.
The conclusions of the study are as
follow:
1.NOX Chemiluminescent analyzers
respond to formaldehyde and
methanol gases when exposed to
high concentrations of these gases
over extended time periods.
2. The response to formaldehyde and
methanol can be severe enough to
cause significant errors in the
measurement of NOX emissions from
methanol cars.
3. Analyzer response to methanol
accounts for most of the error when
measuring NOX emissions from
methanol cars.
4. Reactions involving formaldehyde in
the reaction chamber are the prin-
cipal cause of spurious analyzer
response with samples containing
either methanol or formaldehyde.
S.The most effective way of
eliminating the spurious response is
to clean the reaction chamber
inaccordance with the
manufacturer's instructions.
Further research is recommended |
definitively identify the wavelengths (
light emission associated with th
interference. Bracketing the range (
those wavelengths might b
accomplished through an examination <
the effect of different cut-off filters o
response to formaldehyde. Such a
approach might lead to the selection <
an improved filter which could eliminal
the interference altogether.
It is also recommended that a study t
carried out on other chemiluminescei
analyzers to determine the effect of lor
term exposure to high concentrations <
methanol and formaldehyde. Thus f,
only the Beckman 951A models ha\
been so exposed as a result of emissk
tests on malfunctioning methanol car
Until such studies are completed, or
must assume that all NC
Chemiluminescent analyzers cou
develop problems associated wi
extended testing on methanol car
Therefore, when testing methanol cat
more than the usual care should be tak<
by instrument operators to assure th
their instruments are clean and w(
maintained.
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The EPA author, Peter Gabele (also the EPA Project Officer, see below), is with
the Atmospheric Sciences Research Laboratory, Research Triangle Park, NC
27711.
The complete report, entitled "Investigation of Analyzer Problems in the
Measurement of NOX from Methanol Vehicles," (Order No. PB 89-124
374/AS; Cost: $13.95, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Atmospheric Sciences Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
u. -'L'
Official Business
Penalty for Private Use $300
EPA/600/S3-88/040
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