Evaluation and Use of Stand-Alone Commercial Photolytic
Converters for Conversion of N02 to NO
Keith G. Kronmiller
ManTech Environmental Technology. Inc., P.O. Box 12313, Research Triangle Park, NC 27709
William A. McCIenny
National Exposure Research Laboratory, U.S. Environmental Protection Agency, Research
Triangle Park, NC 27711
ABSTRACT
Two types of stand-alone photolytic converters of nitrogen dioxide (N02) to nitric oxide (NO)
are now commercially available for use with NO, ozone (03) chemiluminescence detector (CLD)
monitors for the measurement of N02. Both units have been tested for interferences resulting
from photolysis of nitrous acid (IIQNQ) and from the decomposition of peroxyl acetyl nitrate
(PAN), One unit (Model 81800, Spectra-Physics Stratford, CT) is based on the use of a
broadband source (short-arc mercury lamp) and incorporates a source cooler. This unit has been
used for two month-long field studies, one in May 2002 and a second in October 2003. The
results indicate that the converter is robust and reliable with conversion efficiencies (CEs) of
35—70% depending on the airflow rate through the converter. The second commercial unit
(Droplet Measurement Technologies Sonoma Technology, Inc., Petaluma, CA) is based on a
light-emitting diode (LED) array with output emission wavelengths centered near 390 nm with
emission bandwidths of typically 20 nm. This unit is being field tested for use as part of ongoing
tests. Based on results so far, the prospect of using one of the stand-alone converters with an
external, heated metal (molybdenum) converter and a chemiluminescence monitor to measure
NO, N02, and NOY (e.g., NO, N02, HN03, HONO, H02N02, N03, N205, and organic nitrate)
seems reasonable.
INTRODUCTION
Commercial chemiluminescence analyzers can easily provide NO measurements with accuracies
well under 0.2 ppb.1 Other reactive nitrogen-containing gases are converted to NO (by a heated
metal, for example) so that, if the conversion is complete, the sum of NO and the other gases is
equal to total reactive nitrogen. Methods for N02 measurements using chemiluminescence
analyzers rely on the fact that NO and N02 are primary emissions so that in cases where they
constitute a health risk, NOx (the sum of NO and N02) is dominant over other nitrogen-
containing compounds. Subtracting NO from NOY then gives an upper limit of N02, and this
limit has been used as the main equivalent method for N02 monitoring to establish compliance
with U.S. ambient air quality standards. However, in modeling the atmosphere, the real
concentration of N02 must be distinguished from NOY minus NO to properly account for
atmospheric chemistry. One option is photolytic conversion of N02 so ambient concentrations
1
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can be determined by subtraction of NO (no converter) from NO plus [CE * NOJ, and then by
dividing the CE, where CE is the conversion efficiency established with N02 calibration gas.
Ideally, these two concentrations are established at the same time so that the subtraction can be
exact. However, in most commercial instruments, the two concentrations are measured
sequentially by passing through or bypassing the converter. As a result, high variability in
ambient concentrations can introduce errors in subtraction (one concentration changes while the
other is being measured). The magnitude of these errors is moderated by using frequent
sequencing and averaging over adjacent cycles. Many research scientists2,3,4 have assembled
photolytic converters for use with chemiluminescence monitors, and at least one commercial
supplier incorporates a photolytic converter as part of a NO and N02 monitoring system.
Apparently, however, no separate photolytic system has been available. Recently, two stand-
alone systems have been placed on the commercial market for use with chemiluminescence
monitors. One is designed along guidelines provided by Ryerson? and uses a broadband light
source. The second is designed for use with light-emitting diodes (LEDs) that can be composition
tuned to emit radiation over a narrow wavelength interval in the 350-400-nm range where NO, is
efficiently photolyzed.
Desirable characteristics of a photolytic converter include a number of interrelated merit
parameters: (1) high converter efficiency; (2) low residence time in the converter (to minimize
the NO. ozone (03) reaction); (3) low photolytic interference equivalence for other compounds,
e.g.. nitrous acid (HONO); (4) low-temperature operation to minimize conversion of thermally
labile compounds like peroxyl acetyl nitrate (PAN); (5) ease of operation and maintenance;
(6) robustness; and (7) low cost. This paper examines most of these parameters. Operation of the
chemiluminescence monitor at "the manufacturer's specifications' for flow rate determines
residence time in the photolysis chamber and the converter efficiency. Since the NO, 03
chemiluminescence monitor measures the rate of arrival of NO molecules, high flow rates
typically increase detection sensitivity while at the same time reducing the efficiency of
photolysis.
Alternative analytical systems that" accurately measure NO, have been developed. Methods such
as the tunable diode laser (TDL),5 laser-induced fluorescence (LIF),rt differential optical
absorption spectrometry (DOAS),7 and direct luminol chemihiminescence8 are all viable
techniques that do not require conversion of NO,. However, these methods are not currently as
prevalent in the U.S. installed instrument base as the chemiluminescenee-based systems. They
are. however, often used for producing high-quality ambient measurements of NO, during
intensive field research programs.
As reported here, two of the Spectra-Physics photolytic converters (Thermo/Oriel Model 81800.
Stratford, CT) were used in the Bay Regional Atmospheric Chemistry Experiment (BRACE) in
May 2002 in Tampa, FL, for one month, and one was used again in the second BRACE in
October 2003. Atmospheric Research Associates (ARA, Piano, TX) used this type of converter
in the Southeastern Aerosol Research and Characterization Study (SEARCH) at eight sites for
over 18 months. Another group, the Lake Michigan Air Directors Consortium and the Illinois
State Water Survey (Champaign, IL) has also used the Thermo/Oriel photolytic converter for
2
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routine measurements. Although newer to the commercial market, the LED-based photolytic
converter has been used recently onboard aircraft as reported by Buhr.9
EXPERIMENTAL METHODS
General Procedures
A diagram of the laboratory test apparatus used during the interference tests is shown in Figure 1.
Test atmospheres of NO in air were produced by dilution of National Institute of Standards and
Technology (NTST)-traceable NO compressed gas standards (Scott-Martin, Inc., Riverside, CA).
NO'free air (zero air) for dilution was produced using compressed air followed by conversion of
any ambient NO to N02 by ozonation. Activated charcoal was then used to remove any trace NO,
and O- from the air. A Model TEI146C calibration/dilution system (Thermo Environmental
Instruments, Franklin. MA) was used for dilution of the NO standard gas using internal mass
flow controllers and was calibrated with a BIOS Model DC-2M (BIOS International, Butler. NJ)
NTST-traceable flowmeter.
NO, test atmospheres were produced by titrating a portion of the generated NO concentration
with G3 using the Model TEI 146C internal ozone generator. A Model 49PS NIST-traceable 03
analyzer was used to verify the 03 used for titrating the NO.
HGNO was produced by reverse permeation of hydrochloric acid (HC1) vapor carried by N2 into
sodium nitrite (NaN02) as described by Febo et al.10 Dilution of the generated HONG vapor took
place outside the multi-port sampling manifold using zero air from the Model TEI 146C. Prior to
experiments, adequate time was allowed for conditioning the system components, which
consisted of 1/8- and 1/4-inch Teflon tubing and fittings as well as the multi-port glass sampling
manifold. The upper limit of HONO concentration was determined using a second
chemiluminescence analyzer operated with a heated metal converter (moly).
IIXO3 was produced using a permeation tube (VICT Metronics, Santa Clara, CA) held inside a
glass chamber within an insulated enclosure. The chamber temperature was regulated at 50 °C.
Selection for either HONO or HN03 was facilitated using Teflon solenoid valves, which could be
activated manually with a switch. The upper limit of HN03 concentration was determined with a
chemiluminescence analyzer in the same way as for HONO.
PAN was prepared for exposure experiments by nitration of tridecane as described by Gaffhey et
al.11 Two methods were used to deliver PAN at low concentrations to the sampling manifold. In
the first, an 80-L Teflon bag was flushed with nitrogen, then an aliquot of the liquified PAN in
tridecane was injected into the bag, followed by refilling with nitrogen. The filled bag was then
transferred to the experimental apparatus laboratory for testing. Li the second method, the
liquified PAN in tridecane was placed into a midget impinger. Zero air was used to carry the
evaporated PAN from the headspace above the liquid to a separate dilution vial. Additional zero
air was then used to reduce the PAN concentration. Using this method, a clean 80-L Teflon bag
was filled from the common manifold for analysis with a GC/ECD system for comparison
purposes. The upper limit of PAN was estimated using a chemiluminescence analyzer in the
same way as for HONO and HN03.
3
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Figure 1: Apparatus Used during Interference Evaluation Study
Vent
BIOS
flowmeter
RH/Temp
monitor
PDaq 55 data
logger
IBM laptop PC
Clean a!r generator
HOMO Source, HNOa Perm
or PAN generator
Thermo/Oriel
{or STI UV-LED}
photolytic converter
TEI42C NOx analyzer
TEI 42S NOx analyzer
TEI 146C calibrator
with ozone generator
4
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Broadband Photolytic Converter
Conversion Stability
Laboratory testing of the Spectra-Physics Model 81800 N02 photolytic converter using the
calibration system shown in Figure 1 demonstrated that CE can vary a few percent. Changes are
most likely caused by degradation of the source lamp inside the device. Changes in the CE
directly affect the outcome of the mathematical calculation of the NO, concentration. The
accuracy of the CE parameter is more important at lower CE values as it has a greater effect on
the calculated N02 concentration.
To maintain measurement accuracy within acceptable quality assurance guidelines, calibration
and CE determination should be performed daily. Under constant conditions of light intensity
and residence time in the photolytic cell, the broadband light source (and CE) was observed to
decrease gradually over time with small intensity variations around the trend line. Frequent
calibrations and NO, CE determinations allow the data acquired between two consecutive cycles
to be adjusted using standard interpolation methods. The Spectra-Physics Model 81800 NO,
converter was used during two field monitoring campaigns of the Bay Regional Atmospheric
Chemistry Experiment (BRACE) in May of 2002 and September-October 2003. In the 2002
experiment, two sites were operated with identical sets of instruments and calibration apparatus.
During the 2003 study, measurements were taken only.at one site. Zero, span, and CE
determinations were performed daily and the results of these show the converter has sufficient
CE stability for high-quality N02 data to be reported.
Table 1 summarizes the CEs determined at the field sites and the analyzers' span response over
the study periods. The data show that from one day to the next the CE stability is less than 1%.
Table 1. Average CE and span stability of the stand-alone N02 photolytic converter and the
chemiiuminescence analyzers used during two month-long field monitoring studies.
Site
Photolytic CE
Average Dally
Change In CE
NO Channel Span
Photolytic
Channel Span
Gandy 2002a
36.7% ± 0.9
-0.19%
0.998 ± 0.07
1.000 ±0.02
Sydney 2002*
41.9% ±2.1
-0.5%
-1.001 +0.03
1.002 ±0.02
Sydney 2003b
80.2% ± 4.2
-0.45%
1.016 + 0.04
1.007 ±0.02
51 EI 42CTL flow rate 1300 cm3/min,
bEnvironnement S.A. AC31M flow rate 350 cm3/min.
Interference of Other Species
The specificity of the photolytic conversion of NO, by broadband light in the wavelength region
of 3 50-400 nm has been investigated by others2 and is a function of absorption cross sections of
species other than NG2 likely to occur in the environment. HO NO is a major potential interferent.
although its absorption cross section is significantly lower over the wavelength range produced
by the photolytic light source.2 Laboratory tests performed using the HONO generation system
supported these assumptions. The data shown in Table 2 summarize the results.
5
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Table 2. HONO interference test data for the Spectra-Physics Mode! 81800 photolytic converter. HONO
CEavg. = 10.4% ±2.0%.
no2
HONO
HONO
Conversion
Conversion
Concentration
Light On
Light Off
Efficiency
Efficiency
Date
ppb
ppb
ppb
%
%
10/08/02 ,
15.7
1.49
0.100
42.0
8.8
10/09/02
15.5
1.47
0.300
42.0
7.5
10/31/02
11.7
1.33
0.060
42.1
10.8
10/31/02
18.0
1.82
0.060
42.1
9.8
11/04/02
20.2
2.12
0.040
42.3
10.3
11/05/02
16.1
. 1.71
0.026
42.3
10.5
11/05/02
16.1
1.69
0.036
42.3
10.3
01/03/03
30.2
2.38
0.020
37.7
7.9
01/09/03*
20.3
2.99
0.010
52.2
14.7
01/22/03
16.8
1.98
0.050
49.0
11.5
01/23/03
16.6
2.06
0.026
49.0
12.3
"Oriel lamp changed 01/09/03.
PAN Interference Test
Other species that potentially cause inaccuracies in measurement ofNO, by photolytic
conversion may not have absorption cross sections within the photolytic lamp spectrum, but may
decompose into N02 and thus undergo photolysis. PAN thermally decomposes during transient
time through the analytical system components because of the elevated temperatures.'2 Tests
were performed to evaluate the extent of the decomposition and its effect on N02 measurements
(see Table 3). Various dilution flows were established with the dynamic dilution system to
provide a range of PAN concentrations. Changes in the chemiluminescence detector (CLD) NO
channel were recorded with and without the photolytic light. The increased NO readings were
then divided by the PAN concentration (measured by the heated molybdenum [moly] converter
NOy channel).
Table 3. PAN interference test data.
PAN Concentration
ppb
Light On
ppb
Light Off
ppb
NOz Conversion
Efficiency
%
PAN
Conversion
Efficiency
%
15.3
0.290
0.034
44
1.7
14.0
0.278
0.027
44
1.8
3.0
0.161
0.051
44
3.4
3.2
0.160
0.040
44
3.7
6
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Decomposition of the' PAN in the system plumbing prior to deliver}' into the photolvtic chamber
was tested by filling an 80-L Teflon bag followed by analysis using a pulse-discharge electron
capture detection (ECD) monitor developed for real-time monitoring.13 Analysis of the PAN
collected during simultaneous NOY measurements showed very little decomposition prior to
delivery into the photolytic system. If PAN decomposed to N02 prior to analysis and collection,
the PAN gas chromatography (GC) with ECD system would report lower values. The GC-ECD
analysis agreed within 5% of the NOY measurements, so there was little decomposition inside the
system before the photolytic converter. The 2-4% CE observed was then thought to be due to
decomposition inside the photolytic chamber caused by the elevated temperature (from the high-
energy UV lamp and heat produced by the internal power supplies).
Solid-Stale UV-LED Photolytic Converter
Conversion Stability
: The Droplet Measurement Technologies-Sonoma Technology, Inc. (STI, Petaluma, CA) UV-
. LED photolytic converter, although packaged in a much smaller form than the Spectra-Physics
broadband light converter, was found to have only half the CE for N02. As discussed earlier,
i variability at low CEs will result in larger uncertainties in the reported N02 concentrations. One
factor that contributes to the CE is residence time within the photolytic chamber. Slower sample
flow rates and longer residence times increase the CE, as shown in Table 4.
Table 4. STI UV-LED photolytic conversion efficiency with analyzers from various manufacturers showing
effect of residence time.
Fiow Rate ¦ Residence Time Conversion Efficiency
CLD Analyzer cm3/m!n sec %
TE1 Model 42S 1440 0.625 21.1 ±0.20
TEI Model 42S 1050 0,857 26.6 ±0.14
TEI Model 42S 1030 0.874 29.0 ±0.66
TEI Model 42CTL 1200 0.750 27.4 ±0.44
Environnement S.A. 750 1.200 43.7 ± 1.50
Model AC31M
Interference of Other Species
Although the radiant ultraviolet (UV) light intensity from the solid-state diode array used in the
STI converter is much less than that provided by the mercury (Hg) lamp used in the Spectra-
Physics converter, it is confined, to a narrower band of wavelengths. This provides less
interference due to photolytic conversion of HONO. This is shown in Table 5.
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Table 5. TE! 42S with ST1 UV-LED in-line with sample inlet {flow rate = 1030 cm3/min, average % BONO
CE = 1.74%+ 0.22).
Date
HONO
Concentration
ppb
Light On
ppb
Light Off
ppb
NOz
Conversion
Efficiency
%
HONO
Conversion
Efficiency
%
01/22/04
7.0
0.15
0.046
29.8
1.5
01/22/04
7.1
0.16
¦ 0.020
29.6
1.9
01/23/04
7.2
0.15
0.016
29.6
1.9
01/23/04
6.9
0.18
0.040
29.6
1.9
01/28/04
6.8
0.16 .
0.060
29.8
1.5
; IINOj Interference Test ;
Based on the lack of significant absorption characteristics close to the available wavelengths
produced by the solid-state UV-LED converter, we did not expect HN02 to be converted. A test
conducted using the Environnement S.A. Model ACS 1M with the STI UV-LED in place of the
internal moly converter showed this is the case. With a HN03 concentration of 19 ppb, the
apparent HN03 CE was found to be 1.1%. .
PAN Interference Tests
The solid-state UV-LED-based STI converter operates at a much lower temperature than the
Spectra-Physics photolytic converter. As a result less thermal dissociation of the PAN into NO;
was expected. The dynamic dilution of PAN head space method was used with simultaneous
collection of a sample bag for GC-ECD analysis. Results are shown in Table 6.
Table 6, PAN interference tests using the STI UV-LED photolytic converter with TEI42s (flow rate = 1030
cm3/mm), using dynamic PAN dilution apparatus with Teflon bag fill during measurement. PAN GC-ECD analysis
agreed within 5%.
Date
PAN
Concentration
ppb
Light On
ppb
Light Off
ppb
N02 Conversion
Efficiency
%
PAN
. Conversion
Efficiency
%
01/29/04
252.00
0.880
0.410
29.8
0.2
01/29/04
8.82
0.048
0.032
29.1
0.2
01/30/04
3.67
0.022
0.016
28.9
0.2 .
¦ These results confirm there was very little decomposition in the system either during delivery to
the converter or inside the STI UV-LED converter.
8
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: FIELD MEASUREMENTS
Broadband Photo lytic Converter
Tampa BRACE Study, May 1—31, 2002
U.S.. Environmental Protection Agency (EPA) scientists and ManTech personnel measured NO
and N02 data taken at two separate locations during the month-long study around the Tampa Bay
area. One site (Gaudy) was located at a Hillsborough County Environmental Protection
Commission air pollution monitoring station near the east end of the Gandy Bridge spanning
Tampa Bay. The second site (Sydney) was located 35 km east-northeast of the Gaudy site on land
belonging to the county water department, south of Sydney Road and east of Valrlco Road in
Brandon, FL.
One of the study participants, ARA, recorded total nitrogen compounds as NOY and also
provided nitric acid (HN03) by denuder difference in real time. Although both the ARA and the
EPA/ManTech data were from point monitoring analyzers, the inlet sampling level for the ARA
instrument was approximately 5 m above the EPA inlet. Thus, a low correlation is possible due
to spatial variations in atmospheric concentrations between the two different sampling probe
heights. ARA provided data from both the Sydney and Gandy sites for the entire study. Their
' data, [NOy — HN03], can be considered the upper limit of [NOx], which, if different from the
sum of [NO] and [NO,], should be due to other nitrogen-containing compounds (e.g., MONO,
H02N"02. N03, N2Os, organic nitrate, and particulate nitrates).
Sydney Site ARA NOr* (NOY—HNOJ versus EPA/ManTech NOx (NO + NOJ ¦
Comparing the ARA NGY* data set with the EPA photolytic NOx set required producing a
combined data set with matching time intervals and with only paired data. After this process,
hourly averages were produced, leading to the data charted in Figures 2 and 3. Interestingly, the
data show the EPA photolytic NOx is lower during the afternoon hours than the ARA NOY*.
Hourly averages are charted in Figure 2 showing the daily trends. Both data sets track very well
(correlation r2 = 0.968), especially during the evening hours when N02 dominates the total NOY.
During the afternoon" when there is less N02, the other mtrogen-containing compounds exhibit a
larger influence and the results obtained with the two instruments separate more.
9
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Figure 2: ARA Hourly Averaged Data versus EPA/MariTech NOx, May 2002
BRACE Study
ARA NOy* (NOy — HN03) arid EPA NOx Data
Sydney Site May 1-31, 2002
bARA NOy
E EPA NOx
n.
c_
a.
2
-I?!
o
Figure 3: ARA NO/ (NOy - HN03) compared to EPA/IVIanTech NOx (NO +
photolytic N02)
ARA MOY*(minus HN03) and EPA NOx (NO + photo N02) Data
BRACE Study Sydney Site May 1-31, 2002
45
y = 1 -0269x + 0.5682
4D
35
¦5 30
Cl
a.
% 25
O
2 20
| 15
0
5
15
35
10
20
25
30
40
45
EPA NOx ppb
10
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SUMMARY
Two stand-alone photolytic N0Z converters, available as commercial products, have been
evaluated. One, based on the use of a broadband UV source from a Hg lamp, is designed to be
used with either research-grade or commercially available 03 chemiluminescence analyzers. This
device was found to be reliable and well engineered. Operation for long periods without operator
adjustments or replenishment of the internally contained coolant was observed during two
month-long intensive field studies in Tampa, FL (BRACE 2002 and BRACE 2003). Experience
shows that because of the rate of change of the UV light due to lamp degradation, although low
(~ -0.4%/day), users should perform a daily zero and N02 span check so the reported data can be
of the highest quality possible. Interferences due to photodissociation of HONO inside the system
have been reported.2 Our evaluations showed this CE can be as high as 15%. Optical filtering may
provide a means of limiting this interference, but during these evaluations no filters were
available. Equivalent PAN CE was as much as 4%, apparently due to thermal conversion of PAN
to N02 in the instrument and converter.
The second stand-alone photolytic converter evaluated (Droplet Measurement Technologies^STI
UV-LED) was also found to be reliable and well engineered. This converter is designed and
packaged in a size that allows it to be installed inside a conventional chemiluminescence
analyzer in place of its internal moly converter. At the time of this work, we have not had the
opportunity of using this converter outside the laboratory. The CE for this system has been tested
with three chemiluminescence analyzers with various sample flow rates. This system was found
to have 40-50% less CE than the broadband system at identical flow rates, although reducing the
inlet flow rate to 750 cmVmiri gives a CE > 40%. Although the CE is much lower than that of the
broadband light system, degradation of the light intensity is less a concern because of the nature
of the solid-state UV light-emitting diodes used in this device. HONO interference tests, using
the more narrow wavelength spectrum that falls outside HONO absorption cross-section features,
confirmed that CE of HONO is less than the broadband lamp converter (2% vs. 15%). PAN and
HNOj were each found to have negligible interference, so these are not considered to be a
problem in ambient measurements of N02.
ACKNOWLEDGMENTS
Thanks to Martin Buhr of Sonoma Technology, Inc., for use of the LED-based photolytic
converter during evaluation tests. Thanks also to Ben Hartsell of Atmospheric Research
Associates, who supplied the ARA comparison data, to Bill Lonneman of EPA's Senior
Environmental Employment Program, who provided the PAN for use during the interference
tests as well as performed the analysis of the co-collected bag samples, and to Stacy Henkle of
KulTech, Inc., who provided the editing expertise.
11
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REFERENCES
1. MeClenny, W.A.; Williams, E J.; Cohen, R.C.: Stutz, J. J. Air Waste Manage. Assoc.
2002,52, 542-562.
2. Ryerson, T.B.; Williams, E.J.; Fehseiifeld. F.C, J. Geophys. Res. 2000,105, .
26,447—26,461.
3. Gao, R.S.; Keim, E.R.; Woodbridge, E.L.; Ciciora, SJ.; Proffitt, M.H.; Thompson, T.I..;
McLaughlin, R.J.; Fahey, D.W.J. Geophys. Res. 1994, 99, 20,673-20,681.
4. Kley, D.; Drummond, J.W.; McFarland, M.; Liu, S.C.J. Geophys. Res. 1981,86,
3153-3161.
5. Sauer. C.G.; Pisario, J.T.; Fitz, D.R. Atmos. Environ. 2003, 37, 1583-1591.
6. Thornton, J.A.; Wooldridge, P.J.; Cohen, R.C. Anal. Chem. 2000, 72, 528—539.
7. Piatt, U.; Pemer, D. J. Geophys. Res. 1980, 85, 7453-7458.
8. Gaffney. J.S.; Bornick, R.M.; Chen, Y.IL; Marlev, N.A.Atmos. Environ. 1998,32,
1445-1454.
9. Buhr. M. Presentation at the Air and Waste Management Association's Symposium on
Air Quality Measurement Methods and Technology, Research Triangle Park, NC. April
2004.
10. Febo, A.; Perrino, C,; Gherardi, M.; Sparapani, R. Environ. Sci. Technol. 1995,29,
2390-2395.
11. Gaffiiey, J.S.; Fajer, R.; Senum, Gl. Atmos. Environ. 1984, 18, 215-218.
12. Kleindienst, T.E.; Res. Chem. Intermed. 1994, 20, 335-384.
13. Lonncman, W.A. U.S. Environmental Protection Agency, Senior Environmental
Employment Program, personal communication, 2004.
KEYWORDS
photolytic converter
nitrogen dioxide
chemiluminescence
PAN
interference
nitrous, acid
12
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DISCLAIMER
This work has been partially funded by the United States Environmental Protection Agency
under Contract 68-D-00-206 to ManTech Environmental Technology, Inc. This paper has been
reviewed in accordance with the Agency's peer and administrative review policies and approved
for presentation and publication. Mention of trade names or commercial products does not
constitute endorsement or recommendation for use.
13
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TECHNICAL REPORT DATA 1
I, Report No.
2.
J PS2004-106S13
' i lillllllllllllll
4. Title and Subtitle
Evaluation and Use of Stand-Alone Commer
cial Photolytic Converters for N02 te NO
A a.
5. Report Date.
31 March 2004
iSutrvtJlsrnst
6. Performing Organization Code
7, Author(s)
Keith G, Kronmiller and William A, McClenny
8. Performing Organization Report No.
9.Performing Organization Name and Address
National Exposure Research Laboratory
109 T.W. Alexander Drive
Research Triangle Park, NC 27709
10. Program Element No.
11. Contract'Grant No.
1 .".Sponsoring Agency Name and Address
National Exposure Research Laboratory
109 T.W, Alexander Drive
Research Triangle Park, NC 27709
13. Type of Report and Period Covered
14.Sponsoring Agency Code
15. Supplementary Notes
16. Abstract
Two types of stand-alone photolytic converters of nitrogen dioxide (N02) to nitric oxide (NO) are now commercially available for use
with NO, ozone (03) chemiluminescence detector (CLD) monitors for the measurements of N02. Both units have been tested for
interferences resulting from photolysis of nitrous acid (HONO) and from the decomposition of peroxyl acetyl nitrate (PAN), One unit
is based on the use of a broadband source and the other on a light-emitting diode (LED) array with output emission wavelengths
centered near 390 nm. Evaluation results indicate that the use of either converter with an external, heated metal (molybdenum)
converter and a chemiluminescence monitor to measure NO, In 02, and NOY seems reasonable.
17. KEY WORDS AND DOCUMENT ANALYSIS
A, Descriptors: Nitrogen dioxide, photolysis, conversion
efficiency, light emitting diode, air monitoring
B. Identifiers / Open Ended Terms | C. COSATI
.
18. Distribution Statement
19. Security Class (This Report) 1 21. No. of Pages
20. Security Class (This Page) 22. Price
Form Available: Network Neighboihood\Knight\Groups\HEASD\Forms\Technical-Report-Data-2220-l
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