ASTM D5156-02(2008)
(Test Method)Standard Test Methods for Continuous Measurement of Ozone in Ambient, Workplace, and Indoor Atmospheres (Ultraviolet Absorption)
Standard Test Methods for Continuous Measurement of Ozone in Ambient, Workplace, and Indoor Atmospheres (Ultraviolet Absorption)
SIGNIFICANCE AND USE
Standards for O3 in the atmosphere have been promulgated by government authorities to protect the health and welfare of the public (5) and also for the protection of industrial workers (6).
Although O3 itself is a toxic material, in ambient air it is primarily the photochemical oxidants formed along with O3 in polluted air exposed to sunlight that cause smog symptoms such as lachrymation and burning eyes. Ozone is much more easily monitored than these photochemical oxidants and provides a good indication of their concentrations, and it is therefore the substance that is specified in air quality standards and regulations.
SCOPE
1.1 This test method describes the sampling and continuous analysis of ozone (O3) in the atmosphere at concentrations ranging from 10 to 2000 μg/m3 of O3 in air (5 ppb(v) to 1 ppm(v)).
1.1.1 The test method is limited to applications by its sensitivity to interferences as described in Section 6. The interference sensitivities may limit its use for ambient and workplace atmospheres.
1.2 The values stated in SI units are to be regarded as the standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: D5156 − 02(Reapproved 2008)
Standard Test Methods for
Continuous Measurement of Ozone in Ambient, Workplace,
and Indoor Atmospheres (Ultraviolet Absorption)
This standard is issued under the fixed designation D5156; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope D5110Practice for Calibration of Ozone Monitors and
CertificationofOzoneTransferStandardsUsingUltravio-
1.1 This test method describes the sampling and continuous
let Photometry
analysis of ozone (O ) in the atmosphere at concentrations
3 IEEE/ASTM SI-10Practice for Use of the International
ranging from 10 to 2000 µg/m of O in air (5 ppb(v) to 1
System of Units (SI) (the Modernized Metric System)
ppm(v)).
2.2 Other Documents:
1.1.1 The test method is limited to applications by its
EPA-600/4-76-005 Quality Assurance Handbook for Air
sensitivity to interferences as described in Section 6. The
Pollution Measurement Systems, Vol I, “Principles”
interference sensitivities may limit its use for ambient and
EPA-600/4-77-027a Quality Assurance Handbook for Air
workplace atmospheres.
Pollution Measurement Systems, Vol II, “Ambient Air
1.2 The values stated in SI units are to be regarded as the 3
Specific Methods”
standard.
3. Terminology
1.3 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the 3.1 Definitions—For definitions of terms used in this test
responsibility of the user of this standard to establish appro- method, refer to Terminology D1356.An explanation of units,
priate safety and health practices and determine the applica- symbols, and conversion factors may be found in Practice
bility of regulatory limitations prior to use. IEEE/ASTM SI-10.
3.2 Definitions of Terms Specific to This Standard:
2. Referenced Documents
3.2.1 absolute ultraviolet photometer—a photometer whose
2.1 ASTM Standards:
design, construction, and maintenance is such that it can
D1356Terminology Relating to Sampling and Analysis of
measure the absorbance caused by O mixtures without refer-
Atmospheres
ence to external absorption standards. Given a value for the
D1357Practice for Planning the Sampling of the Ambient
absorptioncoefficientofO at253.7nmandareadingfromthe
Atmosphere
absolute ultraviolet photometer, O concentrations can be
D1914PracticeforConversionUnitsandFactorsRelatingto
calculatedwithaccuracy.Anabsoluteultravioletphotometeris
Sampling and Analysis of Atmospheres
used only on prepared O mixtures free from interferences, as
D3249Practice for General Ambient Air Analyzer Proce-
in calibration activity.
dures
3.2.2 primary standard—a standard directly defined and
D3631Test Methods for Measuring Surface Atmospheric
established by some authority, against which all secondary
Pressure
standards are compared.
D3670Guide for Determination of Precision and Bias of
3.2.3 secondary standard—a standard used as a means of
Methods of Committee D22
comparison, but checked against a primary standard.
D5011Practices for Calibration of Ozone Monitors Using
3.2.4 standard—an accepted reference sample or device
Transfer Standards
used for establishing the measurement of a physical quantity.
These test methods are under the jurisdiction ofASTM Committee D22 on Air
3.2.5 transfer standard—a type of secondary standard; it is
Quality and is the direct responsibility of Subcommittee D22.03 on Ambient
a transportable device or apparatus that, together with opera-
Atmospheres and Source Emissions.
tional procedures, is capable of reproducing pollutant concen-
Current edition approved April 1, 2008. Published July 2008. Originally
approved in 1991. Last previous edition approved in 2002 as D5156–02. DOI: trations or producing acceptable assays of pollutant concentra-
10.1520/D5156-02R08.
tions.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Available from NationalTechnical Information Service (NTIS), 5301 Shawnee
the ASTM website. Rd., Alexandria, VA 22312, http://www.ntis.gov.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D5156 − 02 (2008)
4. Summary of Test Method welfare of the public (5) and also for the protection of
industrial workers (6).
4.1 Thistestmethodisbasedontheabsorptionofultraviolet
radiation at 253.7-nm wavelength by O and the use of an
5.2 AlthoughO itselfisatoxicmaterial,inambientairitis
3 3
ozone-specific scrubber to generate a reference air stream with
primarily the photochemical oxidants formed along with O in
only O scrubbed from it. A single-cell ultraviolet absorption
polluted air exposed to sunlight that cause smog symptoms
photometerisused,withthecellfilledalternatelywithambient such as lachrymation and burning eyes. Ozone is much more
andO -scrubbedambientair.Theabsorptiontobemeasuredat
easily monitored than these photochemical oxidants and pro-
the lower part of the operating range is extremely small. vides a good indication of their concentrations, and it is
Special precautions and designs must be used to obtain
thereforethesubstancethatisspecifiedinairqualitystandards
accurate results. and regulations.
4.2 The absorption of radiation at 253.7 nm by O at very
6. Interferences
lowconcentrationsfollowstheBeer-LambertLaw.Namely,for
a cell of length d, assuming a constant input ultraviolet
6.1 Any aerosol or gas that absorbs or scatters ultraviolet
intensity, the ratio of the emerging intensities for the cell filled
radiation at 253.7 nm, and that is removed by the O -specific
with sample air, I , and with O -scrubbed air, I , is:
s 3 o scrubber, constitutes an interferent (7) to this test method (8).
Particulate matter can be removed with a poly-
I
s
2~cad!
5 e (1)
tetrafluoroethylene (PTFE) membrane filter.Any type of filter
I
o
can, however, become contaminated and may then scrub O.It
where:
is important to check the O -inertness of such devices fre-
c = the concentration of O , ppm (v),
3 quently.
d = the length of the cell, cm, and
6.2 Some reported positively interfering organic species for
a = the absorption coefficient of O per length unit of d and
a manganese dioxide scrubber are tabulated in Annex A2 of
per concentration unit of c.
this test method. In general, if interferences are suspected, it is
4.3 When(cad)is<<1,asisthecaseforO at253.7nmin
preferabletouseanothertestmethodratherthantotrytoscrub
the concentration range specified for this test method, the
out the interfering agent, since the instability of O makes the
approximation
testing and proving of additional interferant scrubbers particu-
2x
e ' 1 2 x (2)
~ ! larly difficult.
can be used to simplify the signal processing electronics, so 6.3 Water vapor may constitute either a positive or negative
interferant in instruments calibrated with dry span gas (9-12).
that
6.3.1 Improperly polished absorption cell windows may
I 'I ~1 2 cad! (3)
s o
lead to increased signal noise and apparent ozone increases in
and thus
instruments subject to rapidly changing humidity, such as at a
coastal site where instruments may be exposed to frequent
~I 2 I !
o s
c' (4)
shifts between relatively dry terrestrial and moist oceanic air
I ad
o
parcels (8).
4.4 At 1 ppm (v), the high end of the recommended range,
6.3.2 A negative water vapor interference, due to humidity
andapathlengthof50cm,theerrorresultingfromapplication
dependent changes in elution rates of interferences from the
of the above approximation is approximately 1 part in 10000.
ozone scrubber may develop in manganese dioxide scrubbers
4.5 Thus, the concentration of O can be obtained from the
exposed to ambient air (10, 12, 13). This phenomenon is
difference between the signal from the photosensor (often a
described in 7.2.6.
vacuum photodiode) when the contents of the absorption cell
containsampleairfromwhichO hasbeenscrubbed,andwhen
7. Apparatus
it contains sample air containing O .
7.1 Instruments are commercially available that meet the
4.6 At 5 ppb (v) with a 50-cm path length, the absorption is
specifications provided in Annex A1. Note that these specifi-
−6 −5 4
approximately 308×0.005×50×10 or×10 (1-4).
cations do not cover operation where the ambient temperature
4.7 The instrument is calibrated by methods given in Prac-
changes rapidly.
tices D5011 and D5110, which describe the use of an absolute
7.2 Theelementsofthetypicalozone-measuringsystemare
ultraviolet photometer as a primary standard and the qualifi-
shown in Fig. 1.Assembled, they form a photometric ultravio-
cation and use of transfer standards.
let monitor with specifications conforming to those listed in
Annex A1. The components are described in 7.2.1 – 7.2.8.
5. Significance and Use
7.2.1 Ultraviolet Absorption Cell, constructed of materials
5.1 Standards for O in the atmosphere have been promul-
inerttoO ,forexample,PTFE-coatedmetal,borosilicateglass,
gated by government authorities to protect the health and
and fused silica. It shall be mechanically stable so that the
optical alignments of the source, sensor, and any beam-
directingdevices(mirror,prisms,orlenses)arenotaffectedby
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
this test method. changes in ambient temperature (Fig. 1(F)).
D5156 − 02 (2008)
manganesedioxide.Somecompoundsmaybeadsorbedpartly,
producing at first an apparent higher concentration of O ,
followed by a falsely lower concentration as the material is
desorbed (10). Mean O values are not affected by reversibly
adsorbed species when averaging times are much longer than
that of the absorption-desorption cycle, provided that the
possible“negative”O valuesthatresultfromthedesorptionof
the interferant while actual O values are very low or zero are
included in the mean. This may not be true where hourly
averages are calculated by simple arithmetical averaging of
instantaneous values taken within a 1-h period, or where the
instrument contains a zero clamp that prevents negative values
from being output (Fig. 1(D)). After exposure to ambient air,
somemanganesedioxideozonescrubbersmaydevelopanoma-
lous sensitivity to water vapor. Since such anomalous scrub-
bers regain normality at low humidity, their anomalous behav-
FIG. 1 Schematic Diagram of a Typical Ultraviolet Photometer
ior can not be detected during span gas calibrations using dry
zero air. Scrubber effıciency tests must be conducted with wet
span gas to identify such anomalous manganese dioxide
7.2.2 Ultraviolet Lamp—Alow-pressuremercuryvapordis-
cartridges(14, 15).
charge lamp enclosed in a shield to prevent its radiation at 185
7.2.7 Pump—A small air pump to pull the sample air
nm (which generates O ) from reaching the absorption cell
through the instrument (Fig. 1(N)).
(Fig. 1(J)).
7.2.2.1 The lamp output at 253.7 nm shall be extremely 7.2.8 Flowmeter, to verify that air is moving through the
stable,orprovisionshallbemadetocompensateforshort-term instrument (Fig. 1(L)).
variations at 253.7-nm output, for example, by the use of a
7.3 InternalLinesandFittings,inthesamplestreampriorto
lamp-intensity monitor to measure output from the lamp and
the adsorption cell and the scrubber, constructed of PTFE
withelectronicstoadjustthesignalfromtheultravioletsensors
fluorocarbon or other O -inert material.
correspondingly.
7.4 Signal Processing Electronics, containing several dis-
7.2.2.2 Shield, constructed of high-silica glass to remove
tinct elements (Fig. 1(K)):
the 185-nm line and permit the transmission at 253.7-nm
7.4.1 Circuits to condition the signal from the ultraviolet-
radiation (Fig. 1(H)).
sensitive sensor (diode) with short-term stability.
7.2.3 Particulate Filter, installed in the sample line to
7.4.2 Timingandcontrolcircuitstooperatetheflowswitch-
prevent aerosols or particulate matter from entering the mea-
suring system. PTFE fluorocarbon filters with pore sizes ing valves and different phases of the signal conditioning
circuits.
between 0.2 and 5.0 µm shall be used. The filter shall be
replaced frequently since accumulated materials on the filter
7.4.3 Circuitstogeneratemeanvaluesfromthesignalsfrom
may catalyze the breakdown of O into oxygen (Fig. 1(B)). the sensor (diode) interface circuits for the two parts of the
7.2.4 Sensor—Vacuum photodiodes with cesium telluride
cycle, to subtract them, and to output the resultant differences
photocathode sensitivity at 253.7-nm radiation and negligible
in a scaled form. The circuits shall also compensate for
sensitivity to the other mercury lamp lines. The response at
temperature and pressure so that the adsorption measured is
253.7 nm shall be extremely stable over the short-term periods
proportional to the gas density in the absorption cell.
of the sampling cycle, of the same order as the stability
7.4.4 TheconcentrationofO canbeobtainedfromtheratio
demanded of the ultraviolet source. Temperature stabilization
of the sensor (diode) signals when the adsorption cell contains
and a well-regulated photosensor supply voltage shall be
sample air from which O has been scrubbed, to when it
provided to achieve the necessary stability (Fig. 1(E)).
containssampleaircontainingO .Theconversionofthisvalue
7.2.5 Three-Way PTFE Solenoid Valve, constructed with
to parts per million by volume shall include correction for
internal parts of, or coated with, PTFE fluorocarbon or other
ambient temperature and barometric pressure according to the
material that will not catalyze the destruction of O , to route
ideal gas law. The correction can be ignored if errors as great
thesamplethroughortobypasstheO selectivescrubber(Fig.
3 as 65% are acceptable. Some commercially available instru-
1(C)).
ments correct automatically for actual measurement tempera-
7.2.6 Ozone-Specific Scrubber, containing a material that
ture and pressure in their concentration outputs.
selectively catalyzes the destruction of O without altering or
3 7.4.5 Signal processing shall not prevent the output of
addinganyothercompound.Manganesedioxideonasubstrate
negativevalues,whichmayarisefrominstrumentmalfunction,
and heated silver wool have been found generally to perform
from random fluctuations in measurements of I and I in the
s o
this function. However, several aromatic organic compounds
absenceofO ,andfrominterferencesbeingdesorbedfromthe
identified in Annex A2 have been shown to be adsorbed by
O -s
...
This document is not anASTM standard and is intended only to provide the user of anASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately,ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation:D5156–95 Designation:D5156–02 (Reapproved 2008)
Standard Test Methods for
Continuous Measurement of Ozone in Ambient, Workplace,
and Indoor Atmospheres (Ultraviolet Absorption)
This standard is issued under the fixed designation D5156; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 Thistestmethoddescribesthesamplingandcontinuousanalysisofozone(O )intheatmosphereatconcentrationsranging
from 10 to 2000 µg/m of O in air (5 ppb(v) to 1 ppm(v)).
1.1.1 The test method is limited to applications by its sensitivity to interferences as described in Section 6. The interference
sensitivities may limit its use for ambient and workplace atmospheres.
1.2 The values stated in SI units are to be regarded as the standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
D1356 Terminology Relating to Sampling and Analysis of Atmospheres
D1357 Practice for Planning the Sampling of the Ambient Atmosphere
D1914 Practice for Conversion Units and Factors Relating to Sampling and Analysis of Atmospheres
D3249 Practice for General Ambient Air Analyzer Procedures
D3631 Test Methods for Measuring Surface Atmospheric Pressure
D3670 Guide for Determination of Precision and Bias of Methods of Committee D-22 D22
D5011 Practices for Calibration of Ozone Monitors Using Transfer Standards
D5110 PracticeforCalibrationofOzoneMonitorsandCertificationofOzoneTransferStandardsUsingUltravioletPhotometry
E380Practice for Use of the International System of Units (SI) (the Modernized Metric System)
E591PracticeforSafetyandHealthRequirementsRelatingtoOccupationalExposuretoOzoneIEEE/ASTMSI-10 Practicefor
UseoftheInternationalSys-
tem of Units (SI) (the Mod-
ernized Metric System)
2.2 Other Documents:
EPA-600/4-76-005, Quality Assurance Handbook for Air Pollution Measurement Systems, Vol I, “Principles”
EPA-600/4-77-027a, Quality Assurance Handbook for Air Pollution Measurement Systems, Vol II, “Ambient Air Specific
Methods”
3. Terminology
3.1 Definitions—For definitions of terms used in this test method, refer to Terminology D1356. An explanation of units,
symbols, and conversion factors may be found in Practice E380.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 absolute ultraviolet photometer—a photometer whose design, construction, and maintenance is such that it can measure
These test methods are under the jurisdiction of ASTM Committee D-22 on Sampling and Analysis of Atmospheres and is the direct responsibility of Subcommittee
D22.03 on Ambient Atmospheres and Source Emissions.
Current edition approved Sept. 10, 1995. Published November 1995. Originally published as D5156–91. Last previous edition D5156–91.
ThesetestmethodsareunderthejurisdictionofASTMCommitteeD22onAirQualityandisthedirectresponsibilityofSubcommitteeD22.03onAmbientAtmospheres
and Source Emissions.
Current edition approved April 1, 2008. Published July 2008. Originally approved in 1991. Last previous edition approved in 2002 as D5156-02.
ForreferencedASTMstandards,visittheASTMwebsite,www.astm.org,orcontactASTMCustomerServiceatservice@astm.org.For Annual Book of ASTM Standards
, Vol 11.03.volume information, refer to the standard’s Document Summary page on the ASTM website.
Annual Book of ASTM Standards, Vol 14.02.
Available from National Technical Information Service (NTIS), 5285 Port Royal Rd., Springfield, VA 22161, http://www.ntis.gov.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D5156–02 (2008)
the absorbance caused by O mixtures without reference to external absorption standards. Given a value for the absorption
coefficient of O at 253.7 nm and a reading from the absolute ultraviolet photometer, O concentrations can be calculated with
3 3
accuracy.AnabsoluteultravioletphotometerisusedonlyonpreparedO mixturesfreefrominterferences,asincalibrationactivity.
3.2.2 primary standard—a standard directly defined and established by some authority, against which all secondary standards
are compared.
3.2.3 secondary standard—a standard used as a means of comparison, but checked against a primary standard.
3.2.4 standard—an accepted reference sample or device used for establishing the measurement of a physical quantity.
3.2.5 transfer standard—a type of secondary standard; it is a transportable device or apparatus that, together with operational
procedures, is capable of reproducing pollutant concentrations or producing acceptable assays of pollutant concentrations.
4. Summary of Test Method
4.1 This test method is based on the absorption of ultraviolet radiation at 253.7-nm wavelength by O and the use of an
ozone-specific scrubber to generate a reference air stream with only O scrubbed from it. A single-cell ultraviolet absorption
photometer is used, with the cell filled alternately with ambient and O -scrubbed ambient air. The absorption to be measured at
the lower part of the operating range is extremely small. Special precautions and designs must be used to obtain accurate results.
4.2 The absorption of radiation at 253.7 nm by O at very low concentrations follows the Beer-Lambert Law. Namely, for a
cell of length d, assuming a constant input ultraviolet intensity, the ratio of the emerging intensities for the cell filled with sample
air, I , and with O -scrubbed air, I , is:
s 3 o
I
s
2~cad!
5 e (1)
I
o
where:
c = the concentration of O , ppm (v),
d = the length of the cell, cm, and
a = the absorption coefficient of O per length unit of d and per concentration unit of c.
4.3 When (cad) is << 1, as is the case for O at 253.7 nm in the concentration range specified for this test method, the
approximation
2x
e ' ~1 2 x! (2)
can be used to simplify the signal processing electronics, so that
I ' I 1 2 cad (3)
~ !
s o
and thus
~I 2 I !
o s
c ' (4)
I ad
o
4.4 At 1 ppm (v), the high end of the recommended range, and a path length of 50 cm, the error resulting from application of
the above approximation is approximately 1 part in 10000.
4.5 Thus,theconcentrationofO canbeobtainedfromthedifferencebetweenthesignalfromthephotosensor(oftenavacuum
photodiode) when the contents of the absorption cell contain sample air from which O has been scrubbed, and when it contains
sample air containing O .
−6 −5
4.6 At 5 ppb (v) with a 50-cm path length, the absorption is approximately 308 30.005 350 310 or 310 (1-4).
4.7 The instrument is calibrated by methods given in Practices D5011 and D5110, which describe the use of an absolute
ultraviolet photometer as a primary standard and the qualification and use of transfer standards.
5. Significance and Use
5.1 Standards for O in the atmosphere have been promulgated by government authorities to protect the health and welfare of
the public (5) and also for the protection of industrial workers (6) .
5.2 Although O itself is a toxic material, in ambient air it is primarily the photochemical oxidants formed along with O in
3 3
polluted air exposed to sunlight that cause smog symptoms such as lachrymation and burning eyes. Ozone is much more easily
monitored than these photochemical oxidants and provides a good indication of their concentrations, and it is therefore the
substance that is specified in air quality standards and regulations.
6. Interferences
6.1 Anyaerosolorgasthatabsorbsorscattersultravioletradiationat253.7nm,andthatisremovedbytheO -specificscrubber,
constitutes an interferent to this test method (-specific scrubber, constitutes an interferent (7) to this test method (8).
Particulatemattercanberemovedwithapoly-tetrafluoroethylene(PTFE)membranefilter.Anytypeoffiltercan,however,
become contaminated and may then scrub O . It is important to check the O -inertness of such devices frequently.
3 3
Discontinued; see 1990 Annual Book of ASTM Standards, Vol 11.03.
The boldface numbers in parentheses refer to the list of references at the end of this test method.
D5156–02 (2008)
6.2 Some reported positively interfering organic species for a manganese dioxide scrubber are tabulated in Annex A2 of this
test method. In general, if interferences are suspected, it is preferable to use another test method rather than to try to scrub out the
interfering agent, since the instability of O makes the testing and proving of additional interferant scrubbers particularly difficult.
6.3 Water vapor may constitute either a positive or negative interferant in instruments calibrated with dry span gas (8-119-12).
6.3.1 Improperly polished absorption cell windows may lead to increased signal noise and apparent ozone increases in
instruments subject to rapidly changing humidity, such as at a coastal site where instruments may be exposed to frequent shifts
between relatively dry terrestrial and moist oceanic air parcels (8).
6.3.2 A negative water vapor interference, due to humidity dependent changes in ozone scrubbing efficiency, elution rates of
interferences from the ozone scrubber may develop in manganese dioxide scrubbers exposed to ambient air (910, 1112, 13). This
phenomenon is described in 7.2.6.
7. Apparatus
7.1 InstrumentsarecommerciallyavailablethatmeetthespecificationsprovidedinAnnexA1.Notethatthesespecificationsdo
not cover operation where the ambient temperature changes rapidly.
7.2 The elements of the typical ozone-measuring system are shown in Fig. 1.Assembled, they form a photometric ultraviolet
monitor with specifications conforming to those listed in Annex A1. The components are described in 7.2.1-7.2.8.
7.2.1 Ultraviolet Absorption Cell,constructedofmaterialsinerttoO ,forexample,PTFE-coatedmetal,borosilicateglass,and
fused silica. It shall be mechanically stable so that the optical alignments of the source, sensor, and any beam-directing devices
(mirror, prisms, or lenses) are not affected by changes in ambient temperature (Fig. 1(F)).
7.2.2 Ultraviolet Lamp—Alow-pressure mercury vapor discharge lamp enclosed in a shield to prevent its radiation at 185 nm
(which generates O ) from reaching the absorption cell (Fig. 1(J)).
7.2.2.1 The lamp output at 253.7 nm shall be extremely stable, or provision shall be made to compensate for short-term
variations at 253.7-nm output, for example, by the use of a lamp-intensity monitor to measure output from the lamp and with
electronics to adjust the signal from the ultraviolet sensors correspondingly.
7.2.2.2 Shield, constructed of high-silica glass to remove the 185-nm line and permit the transmission at 253.7-nm radiation
(Fig. 1(H)).
7.2.3 Particulate Filter, installed in the sample line to prevent aerosols or particulate matter from entering the measuring
system. PTFE fluorocarbon filters with pore sizes between 0.50.2 and 5.0 µm shall be used.The filter shall be replaced frequently
since accumulated materials on the filter may catalyze the breakdown of O into oxygen (Fig. 1(B)).
7.2.4 Sensor—Vacuum photodiodes with cesium telluride photocathode sensitivity at 253.7-nm radiation and negligible
sensitivity to the other mercury lamp lines. The response at 253.7 nm shall be extremely stable over the short-term periods of the
samplingcycle,ofthesameorderasthestabilitydemandedoftheultravioletsource.Temperaturestabilizationandawell-regulated
photosensor supply voltage shall be provided to achieve the necessary stability (Fig. 1(E)).
7.2.5 Three-Way PTFE Solenoid Valve , constructed with internal parts of, or coated with, PTFE fluorocarbon or other material
that will not catalyze the destruction of O , to route the sample through or to bypass the O selective scrubber (Fig. 1(C)).
3 3
7.2.6 Ozone-Specific Scrubber, containing a material that selectively catalyzes the destruction of O without altering or adding
anyothercompound.Manganesedioxideonasubstrateandheatedsilverwoolhavebeenfoundgenerallytoperformthisfunction.
Available from National Technical Information Service, Springfield, VA 22161.
“Vycor” brand material has been found to be satisfactory.
FIG. 1 Schematic Diagram of a Typical Ultraviolet Photometer
D5156–02 (2008)
However, several aromatic organic compounds identified in Annex A2 have been shown to be adsorbed by manganese dioxide.
Some compounds may be adsorbed partly, producing at first an apparent higher concentration of O , followed by a falsely lower
concentration as the material is desorbed (910). Mean O values are not affected by reversibly adsorbed species when averaging
timesaremuchlongerthanthatoftheabsorption-desorptioncycle,providedthatthepossible“negative”O valuesthatresultfrom
the desorption of the interferant while actual O values are very low or zero are included in the mean.This may not be true where
hourly averages are calculated by simple arithmetical averaging of instantaneous values taken within a 1-h period, or where the
instrumentcontainsazeroclampthatpreventsnegativevaluesfrombeingoutput(Fig.1(D)).Afterexposuretoambientair,some
manganese dioxide ozone scrubbers may develop anomalous sensitivity to water vapor. Ozone scrubbing efficiency is found to
decrease by up to 40% at intermediate relative humidities, leading to negatively biased ozone readings (9(D)).After exposure to
ambient air, some manganese dioxide ozone scrubbers may develop anomalous sensitivity to water vapor. Since such
anomalous scrubbers regain normality at low humidity, their anomalous behavior can not be detected during span gas
calibrations using dry zero air. Scrubber effıciency tests must be conducted with wet span gas to identify such anomalous
manganese dioxide cartridges (14, 15). Since such anomalous scrubbers regain full ozone scrubbing effıciency at low humidity,
their anomalous behavior can not be detected during span gas calibrations using dry zero air. Scrubber effıciency tests must be
conducted with wet span gas to identify such anomalous magnesium dioxide cartridges. .
7.2.7 Pump—A small air pump to pull the sample air through the
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