Производство анализаторов для промышленности и научных исследований с 1989 годаAccuracy and operating characteristics of instruments for ozone content measurements in tlie atmosphere
Accuracy and operating characteristics of instruments for ozone content measurements in tlie atmosphere
Petr I.Domnin, Vladimir P.Chelibanov
State University of St.-Petersburg, St.-Petersburg 198904, Russia
ABSTRACT
Tlie technical data on ozone gas analyzers which are currently produced and operate in Russia and the CIS countries for ozone concentration measurements in llie lower atmosphere are presented. The specific requirements to this type of instruments are formulated and summerized data on their operating and accuracy caracteristics are displayed. Some peculiarities of using optical and chemiluininescent ozone analyzers in view of providing minimum instrument error are discussed. An approach to reasonable combination of advantages of optical and chemiluminescent methods into one unique device are suggested and realized. The unique applications of some instruments under severe conditions of low temperatures in Antarctics on a ground based level and for measuring the ozone content vertical profile in the stratosphere up to 40 km are described. The perspective directions in developing ozone gas analyzers are discussed.
Keywords: ozone monitoring, chemiluininescent sensor, UV-absorption photometer, ozone analyzer,
Keywords: ozone monitoring, chemiluininescent sensor, UV-absorption photometer, ozone analyzer,
1. INTRODUCTION
Ozone is one of the most important components ofterroslrial atmosphere.Being generated? reduced in the high layers of the atmosphere it provides in a large extent an energetic regime of tlie biosphere. Tlie abundance of ozone content in the tropospliere is considered as dangerous for human health. That is why the study of ozone evolution and its measurements represent very importance.
Alt instruments for measuring the ozone content in different conditions operate on the basis of different physical and chemical processes and have different values of parameters such as sensitivity, accuracy, response time etc. Nevertheless, tlie list of ozone analyzers for atmospheric monitoring designed and manufactured in tlie CIS at present is comparatively short. Tlie most widely used of them are presented in Table 2. All ozone analyzers can be divided in four types: chemiluminescent (homogeneous and heterogeneous), optical, electrochemical and colorimetric.
Cheiniluminescent instruments based on the effect of heterogeneous chemilummcscencc on a solid-slate sensor are the best developed.The experience of this instruments operation at tlie stations for background monitoring in Russia and abroad has shown that such ozone analyzers have essential advantages as compared to the other types including optical gas analyzers. These advantage? are higher sensitivity and shorter response time, which have been demonstrated recently by a number of unique geophysical experiments.
Optical gas analyzers have not been widely used in tlie CIS and at present arc produced only as individual units. Similar to optical devices, the production of electrochemical gas analyzers has also not been widely done because of their essential disadvantages were revealed during tlieir operation.
Alt instruments for measuring the ozone content in different conditions operate on the basis of different physical and chemical processes and have different values of parameters such as sensitivity, accuracy, response time etc. Nevertheless, tlie list of ozone analyzers for atmospheric monitoring designed and manufactured in tlie CIS at present is comparatively short. Tlie most widely used of them are presented in Table 2. All ozone analyzers can be divided in four types: chemiluminescent (homogeneous and heterogeneous), optical, electrochemical and colorimetric.
Cheiniluminescent instruments based on the effect of heterogeneous chemilummcscencc on a solid-slate sensor are the best developed.The experience of this instruments operation at tlie stations for background monitoring in Russia and abroad has shown that such ozone analyzers have essential advantages as compared to the other types including optical gas analyzers. These advantage? are higher sensitivity and shorter response time, which have been demonstrated recently by a number of unique geophysical experiments.
Optical gas analyzers have not been widely used in tlie CIS and at present arc produced only as individual units. Similar to optical devices, the production of electrochemical gas analyzers has also not been widely done because of their essential disadvantages were revealed during tlieir operation.
2. CHEMILUMINESCENT OZONE ANALYZERS
The chemiluminesceut method is based on measuring the intensity of light emerging at chemical reaction of the ozone with some organic substances in gas or condensed phases. The value of light intensity depends on analysed gas content and since emission occurs in visible spectrum range a vaste class ofphotomultipliers are available for its registration. The gases (e.g., ethylene) or condensed mailers can be used as reagents. In the last case the sensitive element looks like a porous tablet. Such element has a very higli sensibility to ozone which is not readied with the other methods. The essential disadvantage, a visible decreasing of its sensitivity with time, does not overcome the merits of this method.
But nevertheless it appears for some researchers to declare the absence of any prospect for using the solid chemiluniini scent sensors for atmosphere monitoring. We arc inclined to explain this opinion by misunderstanding complicated chemical reaction mechanism and tlie process of electronical excitation taking place in a sensor cover during interaction process with ozone. Defenders of this point of view reason that this situation does not allow to develop and to manufacture solid ozone sensors with pre-specifiecl and reliable characteristics, so that chemiluminiscent sensors can not be used as means for performing absolute ozone measurements.
On the contrary, another researchers group underlines that chemiluininescent sensors are able to be a reliable foundation for manufacturing ozone and other important atmospheric pollutants analyzers2-3. Their reason is based on carrying out continuous comparison between measured and standard gas mixtures. In this case a high sensitivity and selectivity are achieved; i.e, the features which form key advantages of tlie cliemiluminiscent method. The second point of view, at our opinion, becomes more preferable if the method of heterogeneous chemiluminescence is analytically considered only as a relative one. Ozone-sensitive detectors elements looks themselves solid-state substratum covered by chemiluminesccnt ozone-sensitive layer containing, in turn, polyphenol compound and organic substances. Measurement of ozone concentration is executed by these sensitive elements as follows. A polyphenol compound is oxidi/.cd by the ozone . The products of corresponding chemical reaction occur in excited electronic quantum states. The ozonolitic process, probably ,goes following tlie mechanism of primary attack by ozone-molecule of double carbonic bond of aromatic ring with its following break and isomcrization of terminal carbonic and hydroxile groups. This isomeri/ation leads to an increase of the population of high electronic levels of molecules. Then the energy of excited products of oxidation is transported to organic substance, capable to luminescence. As a result tlie exited molecules of organics emit the photons passing from higher electronic levels to tlie ground state. So one observes the luminescence. Its intensity can be a measure of unknown ozone concentration. It is to note that the number of energetic levels in organic molecule and their mutual disposition in respect to tliat of electronic excited products of polyphenol oxidation by o/one determine the efficiency of energy extractionTrom oxidation products of polyphenol- organics chemical system. Tills in turn gives tlie luminescence efficiency of total composition and consequently the sensor sensitivity in respect to ozone and its life service.
The chemiluminiscent sensor is a mere comparator of the ozone-component of two gas flows (with known and unknown ozone concentrations respectively). Actually if llie measurements should be made with iTiinimum systematic errors under laboratory conditions the optical UV-absorplion method seems to be more preferable. However if tlie measurements are made in a free atmosphere llie intcrferent influence of other gases absorbing at the ozone absorption wavelengths is hardly eliminated. That is why we assume that the combination of both optical and chemiluminescent methods can be considered as promising solution of the atmosphere monitoring problems.
Heterogeneous cliemi luminescence is a light emission resulted from the chemical reaction of ozone with organic substances. Tlie lallers are quite specific in respect to ozone providing by this tlie high sensitivity and selectivity of the chemiluminescent method. As the total quantity of organics coverihg the sensor tablet is limited and can be continuously decreased during measurement process the light intensity value (i.e. measured signal) will change in time. For excluding tlie effect of these processes on the measured o/.one content value llie built-in ozone generator capable to provide periodically specified concentration of analyzed gas is inserted into tlie analyzer set-up. When the sensor is periodically blown through a by a standard mixture with prescribed ozone content the built-in microcomputer normalizes the level of sensor sensitivity. Tlius tlie total measurement cycle is divided in three consequent stages:
But nevertheless it appears for some researchers to declare the absence of any prospect for using the solid chemiluniini scent sensors for atmosphere monitoring. We arc inclined to explain this opinion by misunderstanding complicated chemical reaction mechanism and tlie process of electronical excitation taking place in a sensor cover during interaction process with ozone. Defenders of this point of view reason that this situation does not allow to develop and to manufacture solid ozone sensors with pre-specifiecl and reliable characteristics, so that chemiluminiscent sensors can not be used as means for performing absolute ozone measurements.
On the contrary, another researchers group underlines that chemiluininescent sensors are able to be a reliable foundation for manufacturing ozone and other important atmospheric pollutants analyzers2-3. Their reason is based on carrying out continuous comparison between measured and standard gas mixtures. In this case a high sensitivity and selectivity are achieved; i.e, the features which form key advantages of tlie cliemiluminiscent method. The second point of view, at our opinion, becomes more preferable if the method of heterogeneous chemiluminescence is analytically considered only as a relative one. Ozone-sensitive detectors elements looks themselves solid-state substratum covered by chemiluminesccnt ozone-sensitive layer containing, in turn, polyphenol compound and organic substances. Measurement of ozone concentration is executed by these sensitive elements as follows. A polyphenol compound is oxidi/.cd by the ozone . The products of corresponding chemical reaction occur in excited electronic quantum states. The ozonolitic process, probably ,goes following tlie mechanism of primary attack by ozone-molecule of double carbonic bond of aromatic ring with its following break and isomcrization of terminal carbonic and hydroxile groups. This isomeri/ation leads to an increase of the population of high electronic levels of molecules. Then the energy of excited products of oxidation is transported to organic substance, capable to luminescence. As a result tlie exited molecules of organics emit the photons passing from higher electronic levels to tlie ground state. So one observes the luminescence. Its intensity can be a measure of unknown ozone concentration. It is to note that the number of energetic levels in organic molecule and their mutual disposition in respect to tliat of electronic excited products of polyphenol oxidation by o/one determine the efficiency of energy extractionTrom oxidation products of polyphenol- organics chemical system. Tills in turn gives tlie luminescence efficiency of total composition and consequently the sensor sensitivity in respect to ozone and its life service.
The chemiluminiscent sensor is a mere comparator of the ozone-component of two gas flows (with known and unknown ozone concentrations respectively). Actually if llie measurements should be made with iTiinimum systematic errors under laboratory conditions the optical UV-absorplion method seems to be more preferable. However if tlie measurements are made in a free atmosphere llie intcrferent influence of other gases absorbing at the ozone absorption wavelengths is hardly eliminated. That is why we assume that the combination of both optical and chemiluminescent methods can be considered as promising solution of the atmosphere monitoring problems.
Heterogeneous cliemi luminescence is a light emission resulted from the chemical reaction of ozone with organic substances. Tlie lallers are quite specific in respect to ozone providing by this tlie high sensitivity and selectivity of the chemiluminescent method. As the total quantity of organics coverihg the sensor tablet is limited and can be continuously decreased during measurement process the light intensity value (i.e. measured signal) will change in time. For excluding tlie effect of these processes on the measured o/.one content value llie built-in ozone generator capable to provide periodically specified concentration of analyzed gas is inserted into tlie analyzer set-up. When the sensor is periodically blown through a by a standard mixture with prescribed ozone content the built-in microcomputer normalizes the level of sensor sensitivity. Tlius tlie total measurement cycle is divided in three consequent stages:
- tlie measurement of drift level with blowing through the reactor by ozone free mixture,
- the measurement the calibration sygnal with blowing through the reactor by known ozone content gas mixture from ozone calibrator,
- the measurement of the unknown sygnal level with blowing through the reactor by analysed mixture.
Then tlie microcontroller calculates tlie average ozone concentration of measured gas.
The peculiarity of chemitummesccni sensors is tliat the rate of their sensitivity decrease mainly depends on the total quantity of the gas interacted with sensor surface but not with its absolute concentration. Note the sensor operationing stability also essentially depends on sensor temperature.
Up to nowadays cheinilummescent sensors researches, conducted under laboratory conditions show the opportunities of sensors operation in various modes of gas probe feeding. Under the small rate of gas flow (less than 0,5 1/min) tlie sensor operates in diffusion range, characterized by a strong dependence of chemiluminescence on mass gas consumption. Tliat is why the strict requirements to gas consumption stability arise. But in practice their satisfaction mets with great difficulties. On the other hand under gas m;iss consumption more than 1,5 1/min (kinetical region of tlie process) rather low chemiluminescenee dependence on the gas consumption is observed. Tliat permits to reduce tlie requirements to analyzed gas consumption stability. The sensor operationability at various pressure is an important feature of such instruments. This property become especially important under operation of these sensors in free atmosphere conditions; wlien sensors are used on board ofairplan-laboratories, ozone sondes etc.
The experience of using chemiluminescent analyzers shows that their different characteristics are closely connected each other. For example to attain the highest sensitivity level it is necessary to decrease the dynamic range of the analyzer. Note the absence of any constraints at analyzer response time allows to apply this type of sensors in pulse operating mode. That provides a longer service life of device and allows to extend tlie dynamic range of measured ozone concentrations.
The specially executed investigations have been shown that by corresponding choice of measurement method the chemiluminescent sensors are able to provide high metrological characteristics of analyzers.
The summarized information on solid chemiluminescent sensors produced in Russia is indicated in Table 1. Tablel
^JPai-;> meters ofoxone sensors produced in Russia
Anahzed gas Minimum Dynamic Service life, Responce Impacts of unmeasured (type of sensor) detectable range, hours time, components content, mg/m3 s mkg/m3 S02 NOa NHa
03/K.-3 0.3 0.001-1.000 10,000 0.05
1,0 0.005-0.500 40.000 0.1
________JL5___"ML-l0^00 5000 20 - - -
Note the ozone content measurement method means using ozone generator not less than tlic first class with error level less than 5%.
The peculiarity of chemitummesccni sensors is tliat the rate of their sensitivity decrease mainly depends on the total quantity of the gas interacted with sensor surface but not with its absolute concentration. Note the sensor operationing stability also essentially depends on sensor temperature.
Up to nowadays cheinilummescent sensors researches, conducted under laboratory conditions show the opportunities of sensors operation in various modes of gas probe feeding. Under the small rate of gas flow (less than 0,5 1/min) tlie sensor operates in diffusion range, characterized by a strong dependence of chemiluminescence on mass gas consumption. Tliat is why the strict requirements to gas consumption stability arise. But in practice their satisfaction mets with great difficulties. On the other hand under gas m;iss consumption more than 1,5 1/min (kinetical region of tlie process) rather low chemiluminescenee dependence on the gas consumption is observed. Tliat permits to reduce tlie requirements to analyzed gas consumption stability. The sensor operationability at various pressure is an important feature of such instruments. This property become especially important under operation of these sensors in free atmosphere conditions; wlien sensors are used on board ofairplan-laboratories, ozone sondes etc.
The experience of using chemiluminescent analyzers shows that their different characteristics are closely connected each other. For example to attain the highest sensitivity level it is necessary to decrease the dynamic range of the analyzer. Note the absence of any constraints at analyzer response time allows to apply this type of sensors in pulse operating mode. That provides a longer service life of device and allows to extend tlie dynamic range of measured ozone concentrations.
The specially executed investigations have been shown that by corresponding choice of measurement method the chemiluminescent sensors are able to provide high metrological characteristics of analyzers.
The summarized information on solid chemiluminescent sensors produced in Russia is indicated in Table 1. Tablel
^JPai-;> meters ofoxone sensors produced in Russia
Anahzed gas Minimum Dynamic Service life, Responce Impacts of unmeasured (type of sensor) detectable range, hours time, components content, mg/m3 s mkg/m3 S02 NOa NHa
03/K.-3 0.3 0.001-1.000 10,000 0.05
1,0 0.005-0.500 40.000 0.1
________JL5___"ML-l0^00 5000 20 - - -
Note the ozone content measurement method means using ozone generator not less than tlic first class with error level less than 5%.
OZONE ANALYZER MODEL.652HL01
The 652HL01 was designed and manufactured by the Ukrain Reseach Institute "ANALITPRIBOR" in Kiev. It was based on the reaction of ethylene with ozone wliicli proceeds with chemiluminescence.The ozone concentration in an analysed gas is defined by recording and measuring the light with photomultiplicr. To attain the maximum sensitivity in (lie chamber where tlie reaction with ozone and ethylene takes place an optimum vacuum (about 0.2 atm.) is achieved by means of a micropump.
The gas analyzer 652HL01 is made for a stationary use and consists of 5 units: analysis unit, automatic control unit, electronic unit, a spiral or unit and gas line. A disadvantage of the analyzer is tlic necessity of having a bottle with etiiylene Ihe synthesis and transportation of which entails great difficulties. A number of oilier disadvantages including low reliability and accuracy of measurement and complicated operation made us give up on this instrument. Now the 652HLO 1 is no more manufactured.
The gas analyzer 652HL01 is made for a stationary use and consists of 5 units: analysis unit, automatic control unit, electronic unit, a spiral or unit and gas line. A disadvantage of the analyzer is tlic necessity of having a bottle with etiiylene Ihe synthesis and transportation of which entails great difficulties. A number of oilier disadvantages including low reliability and accuracy of measurement and complicated operation made us give up on this instrument. Now the 652HLO 1 is no more manufactured.
OZONE ANALYZER MODEL.ANKAT 7601
Tlie main concept of the ANKAT 7601 was developed at the Smolensk ANALYTPRIBOR Industrial Association. The ozone analyzer was designed to measure ozone microconcentrations in a ground layer of the atmosphere and in air of industrial premises. The development was finished in 1991. It was shown during the ANKAT 7601 operation experience that the specifications of tlie built-in o/one calibrator had a strong dependence on Temperature. This feature resulted in a large instrumental error of measurement especially for smalt ozone concentrations (less than 50 ppb) and caused the exclusion of this analyzer from use for background ozone monitoring. At present a modification of the ANKAT 76011 ozone analyzer has been performed in the Stock Company "OPTEC" in St.Petersburg to exclude the large temperature dependence of tlie calibrator and primary transformer.
OZONE ANALYZER MODEL 3-02 PI
The 3-02 PI is a portable device for the measurement of ozone microconcentrations in the lower troposphere (ground layer) and in air of industrial premises. It can be used as a part of a movable laboratory for atmospheric pollution monitoring at stations for background measurements under Held conditions. Tlie ozone analyzer is also used for monitoring ozone concentrations to provide safe conditions of work in industry and agriculture.
The 3-02 PI was developed in 1990 and has been manufactured in small lots by the Stock Company "Optics in Ecology" (OPTEC) in St.Petersburg since 1991. The ozone analyzer has a high reproducibility, sensitivityand reliability.
The main feature of the 3-02 PI is a stringent temperature stabilization of the photoreactor of ozone calibrator to provide needed mclrological calibrations in operation. A modification of the 3-02 PI is the ozone analyzer 3-02 PPU with a built-in unit for threshold alarm signalling if ozone concentrations exeed the permissible limit (100 mkg/m3). The 3-02 PP1 is intended mainly for ozone concentration measurements in tlie atmosphere of work areas in industry, but it can be successfully used for the background measurements of ozone eoneeiitralion. Tlie specialized gas analyzer model HGO-02A ( designed on tlie basis of the 3-02P1) has a two step unit of temperature stabilization to provide the operation of gas analyzer under tlie temperature range of-20 C... +20 C and a cycle of programmed control of gas analyzer operation in an automatic mode.
The 3-02 PI was developed in 1990 and has been manufactured in small lots by the Stock Company "Optics in Ecology" (OPTEC) in St.Petersburg since 1991. The ozone analyzer has a high reproducibility, sensitivityand reliability.
The main feature of the 3-02 PI is a stringent temperature stabilization of the photoreactor of ozone calibrator to provide needed mclrological calibrations in operation. A modification of the 3-02 PI is the ozone analyzer 3-02 PPU with a built-in unit for threshold alarm signalling if ozone concentrations exeed the permissible limit (100 mkg/m3). The 3-02 PP1 is intended mainly for ozone concentration measurements in tlie atmosphere of work areas in industry, but it can be successfully used for the background measurements of ozone eoneeiitralion. Tlie specialized gas analyzer model HGO-02A ( designed on tlie basis of the 3-02P1) has a two step unit of temperature stabilization to provide the operation of gas analyzer under tlie temperature range of-20 C... +20 C and a cycle of programmed control of gas analyzer operation in an automatic mode.
OZONE ANALYZER MODEL 202 AD2
The 202 AD2 with a built-in minicomputer has been manufactured by tlie Stock Company "LEC Laboratory" in St.Petersburg for over 3.5 years. It is based on the simple 3-02 PI model and intended for tlie measurement of ozone concentrations in the ground layer of atmosphere. The 202 AD2 can be used in a movable laboratory for pollution monitoring at background stations. A high sensitivity (not worse than 1 ppb) and simplicity (all operations on testing of instrument units, calibration of primary transformer, control of stability of chemiluminescent ozone
Fig.2. Temporal variations of the surface layer ozone cncent rat ions (1) and meteorological parameters of the atmospheric surface layer: air temperature T(2), pressure p(3) and wind direction D(4) from 19 to 27 September 1989 in the Weddell Sea,-”
The operation of the OPTEC and LEC chemiluminescent ozonemeters under low temperatures (fig.2 ) let us to conclude that it is possible to use these instruments for background measurements of ozone concenlralions in the polar latitudes. A portion of the multiday experiment for measurement of surface ozone concentrations performed on the route of the "TransAnlarctics" Expedition in 1989-1990 under rather low temperatures (down to -40 C )'.
The chemiluminescent gas analyzers are the best for the measurement of fast temporal variations of ozone concentrations. These studies arc of great interest for geophysists in the USA, Canada and Russia.
The optical ozoncmelers considered by tlic World Meteorological Organization as primary analyzers for background atmosphere monitoring in Russia and the CIS are not produced in large quantities. Measurements are carried out mainly with imported instruments and devices manufactured in Russia individually.
Analisis of currently developed and produced ozone analyzers allows to formulate the principal problems resulting in absence ofcompetitionable instruments for ozone monitoring at native market.
In UV photometry region: it is connected with missing of UV emission sources having high radiance at small dimensions of irradiated coi-p at wavelength near 254 nm. Another problem is related to the lack of plan highohm resistors, amplyfiers and U-I -transformers with high transformed slope. Increased, at present, import possibilities allow to solve such problems.
In chemiluminescent ozone analisis region: as showed the practice chemiluminescent detectors provide liigh operating characteristics only in combination with stable source of calibrated gas mixtures from ozone generator, so that the developcment and production of ozone generators of first category able to provide and support ozone content level in gas mixture must be considered as of great importance. Their precision must not be more 3-5%. Using of eleetrodless lamps of middle power of VRM-1 helps to resolve the problem providing thermal stabilization of lamp itself, blowened-through photochemical reactor and key units of electronics. In order to check output intensity stability in UV region shorter 250 nm it is necessary to introduce light flux feedback, as only current feedback cannot provide desired stability of lamp radiance used for photolytic dissociation of molecular oxygene.
In the laboratory of one of authors an attempt for developing ozone analyzer of new generation in extended degree lacking the above numerated defects. In analyzer model FHL-104 it managed to join advantages of heterogeneous chemilumineseence (high sensitivity and selectivity, low response time) and optical UV-absoqition (low systematic error, high reliability). Block-scheme of the analyzer FHL-104 is shown in Fig.3. Laboratory tests demonstrated tlie high operationing characteristics of the instrument. 0/one content dynamical range - 5.0-1000 mkg/m3 (2-500 ppb) Minimum detectable concentration - 1.0 mkg/m3 (0.5 ppb) Precision - about 10% Weight - less 16 kg.
At present an instrument analogic to FHL is designed by joint efforts of canadien Atko Systems Inc. and russian OPTEC firms.
sensitive sensor sensitivity are performed automatically) make it possible to use this instrument for multiday routine observations for ozone concentration in the atmosphere. The ozone analyzer can be connected with a PC AT/XT through the RS232 interface.
The AD-203 is a specialized instrument designed on the basis ofthe202 AD2 gas analyzer and intended for the background measurement of ozone concentrations with a fast response time of 0.05 sec.
Fig.2. Temporal variations of the surface layer ozone cncent rat ions (1) and meteorological parameters of the atmospheric surface layer: air temperature T(2), pressure p(3) and wind direction D(4) from 19 to 27 September 1989 in the Weddell Sea,-”
The operation of the OPTEC and LEC chemiluminescent ozonemeters under low temperatures (fig.2 ) let us to conclude that it is possible to use these instruments for background measurements of ozone concenlralions in the polar latitudes. A portion of the multiday experiment for measurement of surface ozone concentrations performed on the route of the "TransAnlarctics" Expedition in 1989-1990 under rather low temperatures (down to -40 C )'.
The chemiluminescent gas analyzers are the best for the measurement of fast temporal variations of ozone concentrations. These studies arc of great interest for geophysists in the USA, Canada and Russia.
The optical ozoncmelers considered by tlic World Meteorological Organization as primary analyzers for background atmosphere monitoring in Russia and the CIS are not produced in large quantities. Measurements are carried out mainly with imported instruments and devices manufactured in Russia individually.
Analisis of currently developed and produced ozone analyzers allows to formulate the principal problems resulting in absence ofcompetitionable instruments for ozone monitoring at native market.
In UV photometry region: it is connected with missing of UV emission sources having high radiance at small dimensions of irradiated coi-p at wavelength near 254 nm. Another problem is related to the lack of plan highohm resistors, amplyfiers and U-I -transformers with high transformed slope. Increased, at present, import possibilities allow to solve such problems.
In chemiluminescent ozone analisis region: as showed the practice chemiluminescent detectors provide liigh operating characteristics only in combination with stable source of calibrated gas mixtures from ozone generator, so that the developcment and production of ozone generators of first category able to provide and support ozone content level in gas mixture must be considered as of great importance. Their precision must not be more 3-5%. Using of eleetrodless lamps of middle power of VRM-1 helps to resolve the problem providing thermal stabilization of lamp itself, blowened-through photochemical reactor and key units of electronics. In order to check output intensity stability in UV region shorter 250 nm it is necessary to introduce light flux feedback, as only current feedback cannot provide desired stability of lamp radiance used for photolytic dissociation of molecular oxygene.
In the laboratory of one of authors an attempt for developing ozone analyzer of new generation in extended degree lacking the above numerated defects. In analyzer model FHL-104 it managed to join advantages of heterogeneous chemilumineseence (high sensitivity and selectivity, low response time) and optical UV-absoqition (low systematic error, high reliability). Block-scheme of the analyzer FHL-104 is shown in Fig.3. Laboratory tests demonstrated tlie high operationing characteristics of the instrument. 0/one content dynamical range - 5.0-1000 mkg/m3 (2-500 ppb) Minimum detectable concentration - 1.0 mkg/m3 (0.5 ppb) Precision - about 10% Weight - less 16 kg.
At present an instrument analogic to FHL is designed by joint efforts of canadien Atko Systems Inc. and russian OPTEC firms.
sensitive sensor sensitivity are performed automatically) make it possible to use this instrument for multiday routine observations for ozone concentration in the atmosphere. The ozone analyzer can be connected with a PC AT/XT through the RS232 interface.
The AD-203 is a specialized instrument designed on the basis ofthe202 AD2 gas analyzer and intended for the background measurement of ozone concentrations with a fast response time of 0.05 sec.
3. ELECTROCHEMICAL OZONE ANALYZERS
The semi-automatic ozone analyzer tlie "Atmosfera-2" model (later modified as "Atmosfera-PM" model) was designed in Smolensk and provides the measurement of ozone and chlorine content in the atmosphere. The instrumentis made in a portable design with a battery voltage supply. The gas analyzer has been designed for the determination of ozone content in air with concentrations of main atmospheric pollutants no more than: S02 - 0.8 mg/m3; H2S - 0.01 ing/m3; C02 - 0.6 ing/m3; N02 -0.1 mg/m3. The determination of ozone concentrations is based on tlie measurement of current on the platinum electrode from reduction of bromine formed in the reaction between ozone and sodium bromite:
03 + 2NaBr -> Br2 + Oi + 2Na + 0
The reaction proceeds in a measurement chamber of the clectrochemical cell. For ozone determination the reductants (S02, PhS) have an interfering influence so measurements can be made with no fillers only in pure air.The experience of their operation showed that they are not acceptable because of their low accuracy for atmospheric monitoring. Some years ago they were transfered in the class of gas detectors. Since 1990 the "Atmosfera-2" has been out of production and at present only a few instruments aroused in the CIS.
In 1991-1992 in the Petersburg enterprise 'ATMON" an attempt of production of electrochemical gas analyzer ofthc ELMA45B1 type was made for monitoring problems. Employment experience has revealed series defects related to their sensibility and selectivity. Now only a few units are produced.
Since 1996 in St.-Petersburg the small dimension gas analyzer MGL-19 is developed and produced. This device includes elect rochemical sensor of tlie finn City Technology Ltd (England) model 3.0Z. Dynamical region of measured concentration is 0-4 mg/m3 with concentration resolution equal to 0.04 mg/m3. It is capable to overcome concentrations up to 10 mg/m3. This instruments may be considered as analyzer of threshold type, capable provide quantitative measurements only for ozone contenls.,higer limit level in working areas. At doubtless advantages (inexpensive and liglit wciglit up to 0.6 kg) the MGL-19 is characterized by common for electrochemical devices disadvantage-;: low response rate and sensitivity and selectivity. As sliowed laboratory tests it lias increased sensibility to water vapour and for operating in normal regime the high stability of blown through reactor air flow speed is necassary. Tliese features make this type of instruments rather inconvenient at diffusion regime of blowing analyzed gas.
03 + 2NaBr -> Br2 + Oi + 2Na + 0
The reaction proceeds in a measurement chamber of the clectrochemical cell. For ozone determination the reductants (S02, PhS) have an interfering influence so measurements can be made with no fillers only in pure air.The experience of their operation showed that they are not acceptable because of their low accuracy for atmospheric monitoring. Some years ago they were transfered in the class of gas detectors. Since 1990 the "Atmosfera-2" has been out of production and at present only a few instruments aroused in the CIS.
In 1991-1992 in the Petersburg enterprise 'ATMON" an attempt of production of electrochemical gas analyzer ofthc ELMA45B1 type was made for monitoring problems. Employment experience has revealed series defects related to their sensibility and selectivity. Now only a few units are produced.
Since 1996 in St.-Petersburg the small dimension gas analyzer MGL-19 is developed and produced. This device includes elect rochemical sensor of tlie finn City Technology Ltd (England) model 3.0Z. Dynamical region of measured concentration is 0-4 mg/m3 with concentration resolution equal to 0.04 mg/m3. It is capable to overcome concentrations up to 10 mg/m3. This instruments may be considered as analyzer of threshold type, capable provide quantitative measurements only for ozone contenls.,higer limit level in working areas. At doubtless advantages (inexpensive and liglit wciglit up to 0.6 kg) the MGL-19 is characterized by common for electrochemical devices disadvantage-;: low response rate and sensitivity and selectivity. As sliowed laboratory tests it lias increased sensibility to water vapour and for operating in normal regime the high stability of blown through reactor air flow speed is necassary. Tliese features make this type of instruments rather inconvenient at diffusion regime of blowing analyzed gas.
4. OPTICAL OZONE ANALYZERS
The absorption of light between 200 and 300 nm by o/one(the Hartly band) can be used for detnnination and monitoring of ozone concentration in tlie gas phase. Tlie metliod is based on the Beer-Lambert absorption law which is expressed in the form: I^oexpt-k'-C^d), orhi(I/Io)=k*C*d, wherein: I and Io arc the measured UV intensities passing tlie absorption celt, respectively witli and witliout ozone present, C is the ozone concentration in mol/L; d is the internal length of the absorption cell in cm, and k is the molar absorption index in L/mol*cm.
At the maximum of absorption band (260 nm), the value of k is 3025 L/mol'!'cm. When using low-pressure mercury lamp sources emitting the 253,7 nm wavelength, the k-valuc to be considered is 3000+-30 L/mol*cm, .i.e., an instrumental accuracy of 1%.
When using low pressure mercury (Hg) lamps, light at wavelengths higher than 253,7 nm shall be cut off by appropriate filters and for light emitted at lower wavelengths, filters and/or specific diode detectors can be used. A monochromatism of ±2 nm shallbe achieved. Controlled electrical current feed to the lamps shall guarantee a constant liglit intensity output Io, even at fluctuations in the mains voltage.
Only ozone-resistant materials shall be used for transfer of sample gas: such as glass, quartz, PTEF, stainless steel 316 or higher grade.
To avoid ozone loss by self-decomposition, a minimum gas flow of IL/min shall flow through the light absorption cell, and, the overall delay between the sampling point and the exit of the measuring cell shall be less than one minute.
Generally the optical gas analyzers are of single-beam or double-beam type photometers. In the first case the values of I and Io are measured in succession one after another and tlie device includes one cell and one detector. The devices of second types have two cells (ozone-tree cell gas sample cell) and two detectors, so that the intensities measurements can be made simulteneously. This way of operation allows to exclude both the soures intensity fluctuations and the photometer transmissions changes during all measurement cycle,
In the single-beam type instruments, automatic checks of zero value with ozone-free gas shall be built-in in the automated system of monitoring, e.g., every 30 to 60 min
At the maximum of absorption band (260 nm), the value of k is 3025 L/mol'!'cm. When using low-pressure mercury lamp sources emitting the 253,7 nm wavelength, the k-valuc to be considered is 3000+-30 L/mol*cm, .i.e., an instrumental accuracy of 1%.
When using low pressure mercury (Hg) lamps, light at wavelengths higher than 253,7 nm shall be cut off by appropriate filters and for light emitted at lower wavelengths, filters and/or specific diode detectors can be used. A monochromatism of ±2 nm shallbe achieved. Controlled electrical current feed to the lamps shall guarantee a constant liglit intensity output Io, even at fluctuations in the mains voltage.
Only ozone-resistant materials shall be used for transfer of sample gas: such as glass, quartz, PTEF, stainless steel 316 or higher grade.
To avoid ozone loss by self-decomposition, a minimum gas flow of IL/min shall flow through the light absorption cell, and, the overall delay between the sampling point and the exit of the measuring cell shall be less than one minute.
Generally the optical gas analyzers are of single-beam or double-beam type photometers. In the first case the values of I and Io are measured in succession one after another and tlie device includes one cell and one detector. The devices of second types have two cells (ozone-tree cell gas sample cell) and two detectors, so that the intensities measurements can be made simulteneously. This way of operation allows to exclude both the soures intensity fluctuations and the photometer transmissions changes during all measurement cycle,
In the single-beam type instruments, automatic checks of zero value with ozone-free gas shall be built-in in the automated system of monitoring, e.g., every 30 to 60 min
ANALYZER MODEL AF-4 OZONE
The AF-4 photometric analyzer is intended for measurement of low ozone concentrations in gas mixtures in the range of 0.01 - 10 mg /m^The device lias a microprocessor control and it can be used as an indicator of exceeding the limiting permissible ozone concentrations in air, it can send current information by the computer communication line.
The instrument has been made for both laboratory and portable use.It is intended for operation under ambient temperature of-50 C to +50 C humidity up to 90 % and atmospheric pressure of 500-800 mm Hg. At present the instruments are manufactured in single units by the Moscow enterprise "Fototch".
The instrument has been made for both laboratory and portable use.It is intended for operation under ambient temperature of-50 C to +50 C humidity up to 90 % and atmospheric pressure of 500-800 mm Hg. At present the instruments are manufactured in single units by the Moscow enterprise "Fototch".
OZONE ANALYZER MODEL F101
The F101 ozone analyzer has been designed for measurement of ozone concentrations in the surface atmosphere under field condition and it can also be used used as a reference means of measurement in laboratory research work.
The F101 was developed on the single-beam optical scheme. It is capable of a large dynamic range of measurement of ozone concentrations. The analyzer has a liigli sensitivity and accuracy. It is controlled by the PC AT/XT through the parallel interface.
The F101 was developed on the single-beam optical scheme. It is capable of a large dynamic range of measurement of ozone concentrations. The analyzer has a liigli sensitivity and accuracy. It is controlled by the PC AT/XT through the parallel interface.
OZONE ANALYZER MODEL F103
This device was designed and produced in the Stock Company "OPTEC" in the St.-Petersburg from 1994. It can operate in field conditions and control the ozone content in the industrial areas. Besides it can be used as sample instrument in executing metrological observations. The analyzer is of double-beam type lias a high sensitivity, precision, stability and and large dynamical range of order 100.000. The built-in microcomuter supplies the different operating regimes. The optical cells of 20 mm diameter and 500 mm length are made of quartz, their ends are closed by quartz windows. Temperature gradients and mechanical stress between cells are reduced to minimum. The SiC- photodiodes are used as detectors in tlie instrument. Photodiodes arc isolated electrically from each other and placed on common metal support to provide crystals temperatures identity. The sensibilities descrepancy of two photodiodes must not exceed 10%.The high stability light source is imolemented on base of mercury-quartz lamp of 13 mm diameter excited by high frequency (230 MH/-) generator of 7.5 W (under forced wanning regime) and 2.8 W in steady state. The source has temperature stabilization at 50 °C with precision 0.2 °C.
5. CONCLUSIONS
The solid-state chemiluminescent ozone meter is a main type of ozone analyzer for atmosphere monitoring in Russia. The chemiluminescent ozone sensitive element is based on organic materials which arc tlie primary transformer in the gas analyzers. As laboratory and background inslrumens tests shown chemiluminescent ozoncmeters have a high transfer function linearity (Fig.l) and high sensitivity (Fig.2)1-3.
Fig. 1. Results of analysis of transfer function linearity for chemiluminescent ozone sensor. Produced on a test bench ofCapman LAB, Canada, AES. 1 - mirror, 2 - semitransparant plate, 3 - Hg-lamp, 4,5,6 - solenoid valves, 7,8 - light traps, 9 - adjusted diaphragm, 10 - analog output. 11 - photomulliplicr, 12 - pulse generator, 13 - microprocessor.
Fig.3. The ozone analyzer model FHL setup.
It should be noted that there is a fourth type of ozone analyzer which can be designated as single or double frequency lazer ozone analyzers. This type as with optical gas analyzers is not widely used in Hie CIS as far as we know, this laser ozone analyzer has been designed by the reseachers of the Tomsk Institute of Atmospheric Optics to study the stratospheric ozone profiles up to the altitudes of 50 km [6]. The intensive bands of o,.one absorption in the UV spectral region and the availability of such powerful light sources as the excimcr Xe-Cl-lasers operating at wavelength 308 nm provide a succesfull application of such lidars for ozone monitoring in the troposphere and stratosphere. Taking into account Hie effects of aerosol and molecular light scattering in the UV spectral region and light absorption by the water vapor molecules in the troposphere the use of double frequency mode of such lidars is preferable. This mode of operation is realized by frequency conversion of Xe-Cl-lascr radiation using a Raman cell. Under hydrogen pressure in (lie cell equal lo 18 aim sueli lidar provides at its output two liglit beams at ttie wavelengths 308 and 353 nm with pulse energy 50 mJ and 30 mJ respectively and repetition frequency 50 - 100 Hz.Thc spatial resolution of these instruments is 500 m and 15 - 30 nun respectively.
Fig. 1. Results of analysis of transfer function linearity for chemiluminescent ozone sensor. Produced on a test bench ofCapman LAB, Canada, AES. 1 - mirror, 2 - semitransparant plate, 3 - Hg-lamp, 4,5,6 - solenoid valves, 7,8 - light traps, 9 - adjusted diaphragm, 10 - analog output. 11 - photomulliplicr, 12 - pulse generator, 13 - microprocessor.
Fig.3. The ozone analyzer model FHL setup.
It should be noted that there is a fourth type of ozone analyzer which can be designated as single or double frequency lazer ozone analyzers. This type as with optical gas analyzers is not widely used in Hie CIS as far as we know, this laser ozone analyzer has been designed by the reseachers of the Tomsk Institute of Atmospheric Optics to study the stratospheric ozone profiles up to the altitudes of 50 km [6]. The intensive bands of o,.one absorption in the UV spectral region and the availability of such powerful light sources as the excimcr Xe-Cl-lasers operating at wavelength 308 nm provide a succesfull application of such lidars for ozone monitoring in the troposphere and stratosphere. Taking into account Hie effects of aerosol and molecular light scattering in the UV spectral region and light absorption by the water vapor molecules in the troposphere the use of double frequency mode of such lidars is preferable. This mode of operation is realized by frequency conversion of Xe-Cl-lascr radiation using a Raman cell. Under hydrogen pressure in (lie cell equal lo 18 aim sueli lidar provides at its output two liglit beams at ttie wavelengths 308 and 353 nm with pulse energy 50 mJ and 30 mJ respectively and repetition frequency 50 - 100 Hz.Thc spatial resolution of these instruments is 500 m and 15 - 30 nun respectively.
6. REFERENCES
- Boyarsky V.I., Guliaev Y.N., Chelibanov V.P. "Changeability of surface ozone concentration in various orographic and weatlier conditions in Antarctica", Simp.on Atmospheric Chemistry of the Antarctic Region.3 - 6 June 1991, Spec.Reporf 91-10, p.5, Boulder, Colorado,
- Lebedev S.G., Chelibanov V.P. "Special features of ozone concentratio measurement by chemiluminescent gas analyzer in free atmosphere"/'m“^cri(m of Higher Schools, Atmospheric ozone, St.Petersburg, 1991.
- Yurganov L.N. "Surface layer zozne above the WeddlVell sea during the Antarctic spring",Antarctic Science. 2(2), p. 169. 1990
- Lebedev S.G., Chelibanov V.P. Book Absir. of the Second AH-UnionConference on Ozone Generation and Application: OZONE-91. Moscow, p.121, 1991.
- KononkovV.A., PerovS.P. Transactions of the Central Aerological Observatory.p.1\, 1981
- Lebedev S., Chelibanov V. "Development of a new solid bodymeasuring clement for cmiluminescent ozone analyzer", CHEMRA WN V 11, A World Conference on Chemistry of the Almosphere:Its Impact, on Global Change, 2-6 Dec., 1991, Baltimore, Maryland, Abstract Book.pAI.
- 7.Bourlakov V.D.. El'nikov A.V., Zuev V.V. and all. .Optics of Atmosphere, 5..1022, (1992)
Table2
| Main specifications ot ozone analyzers produced in Llo tor atmos | here monitoring | ||||||
|---|---|---|---|---|---|---|---|
| N | Type | Enterprise-manufacturer | Range uf measured content, млн-1 | Minimum detectable content, ppb | Accuracy, (% or млн-1) | Response time, s | Weight / di mensions kg, cm |
| 1 | At m o sphere PM (electro chemical sensor) | Smolensk, Russia, ANALIT-PRIBOR | 0-0.91 0-0.45 | 11 | 20% | 420 | 20kg 490* 19.6* 29.3 |
| 2 | 652HL-01 (chcmi luminescent sensor) | Kiev,Ukrain ANALIT-PRIBOR | 0-0.23 0-0.68 0-0.23 0-0.68 | 2.3 | 20% | 180 | 80kg, 55.0* 92.0* |
| 3 | ANKAT-7601 (chemilumine-scent sensor) | Smolensk, Russia, ANALIT-PRIBOR | 0-0.045 0-0.45 | 13.6 | 3.4 ppb for c= 14 ppb 0.68+0.09 l*c for c=14ppb, where c-measured content | 30 | 15kg, 60.0* 39.5^ 20.5 |
| 4 | 302P1 (chcmi luminescent sensor) | St.Pcli-sburg. Rissia, OPTEC | 0-0.250 | 2 | 15% | 1.0 | 4.5 kg, 29.0* 21.0* 10.0 |
| 5 | 302PPU (chemi-luminescent sensor) | St.Petersburg, Russia, OPTEC | 0-0.250 | 1 | 15% | 1.0 | 4.5 kg, 29.0* 21.0* 10.0 |
| 6 | ELMA45B1 (elecli-ochemi-cal sensor) | St.Petersburg, Russia, ATMON | 0-0.45 | 20% | 5kg | ||
| 7 | 202AD2 (chemi-lumincscent sensor) | St. Petersburg Russia OPTEC | 0-0.999 | 1 | 10% | 10 | 8kg, 43.0* 37.0* 8.0 |
| 8 | AF-4 (UV-absorption) | Moscow, Russia, PHOTOTEH | 0-4.55 | 5 | 300 | 60.0*40.0* 15.0 | |
| 9 | F-103 | St,Petersburg, OPTEC | 0-1.000 0-100.000 | 0.5 | 0.001 | 10 | 14kg, 19.0*14.0* 75.0 |
| 10 | OZONE-PDK (UV-absorption) | Angarsk, Russia, HIMAVTO-MATIKA | 0-0.25 | 25 | 12% | 180 | 21.5kg, 48.5*20*38, and 6.8*9.5 9.0 |
| 11 | MGL-19-03 (elect roche-mical) | St.Petersburg, OPTEC | 0-2.00 | 20 | 20% | 30 | 0.6 kg, 17.0*8.5* 4.0 |
