1. Introduction |
Many chemical substances have harmful effects on human health. As a result of our production, consumption and lifestyles, we release chemical substances to the environment, where they become harmful contaminants that pollute the areas of the environment, including the atmosphere, water, and soil (see Figure 1).
Volatile organic compounds (VOC) are representative of such harmful pollutants. VOCs released into the environment cause smog. They are also a contributing factor to sick house syndrome and sick car syndrome. They pose a grave concern to the human body.
Of the VOCs, benzene, toluene, and xylene are carcinogenic and pose danger to cranial nerves even at low concentrations. Thus monitoring of these substances is critical.
NTT has developed portable hazardous gas detection technology for detecting VOCs. This hazardous gas detection technology can not only detect dilute levels (ppb*: 10-9 level) of benzene, toluene and xylene in the atmosphere, it can also detect components of benzene, toluene and xylene in solutions with dissolved VOCs.
The size of a device using NTT's Hazardous Gas Detection Technology measures 33.5cm wide, 15.5cm deep, and 18cm tall, making it portable and useful for onsite environmental monitoring. This technology is expected to have applications in the future such as measuring atmospheric and water quality.
* ppb：parts-per-billion（10-9 =μg/kg ）
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| Figure 1 Pollution of the environment |
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2. Fields to which the Hazardous Gas Detection Technology can apply |
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| Hazardous Gas Detection Technology |
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| (1)Emitted gas monitoring |
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| Detection equipment using NTT's Hazardous Gas Detection Technology can detect dilute levels (ppb level) of benzene, toluene and xylene gases even in an environment where emitted gases, including numerous hazardous gases, have become like background noise. | |
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| NTT's Hazardous Gas Detection Technology can detect dilute levels (ppb level) of toluene and xylene gases in buildings. Using a ventilation system and a monitoring system to determine results is demanded these days. |
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| Water quality measurement | |
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| (3)Discharged water monitoring |
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| By combining (1) technology for vapor separation of benzene from solution and (2) technology for drying/concentrating evaporated benzene, NTT's Hazardous Gas Detection Technology can detect benzene in solution, allowing benzene in flowing fluids to be detected. | | |
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2.1 Emission Gas Monitoring |
As mentioned above, volatile organic compounds (VOCs) are principle components of photochemical oxidants (Ox). They primarily originate from automobile exhaust gases. Photochemical oxidants form smog, causing harm to human health. Thus it is necessary to accurately measure their concentration in the atmosphere.
Of the VOCs, aromatic compounds such as benzene and xylene are not only a cause of photochemical oxidants, they are also believed to contribute to increasing the concentration of suspended particulate matter (SPM), which pollute the atmosphere.
Therefore, to make advancements in measures against VOCs, what is required is detecting their main components and knowing their behaviors. What is required in VOC measuring equipment from now on are (1) the ability to distinguish components and (2) the ability to continuously measure changes in concentration. Such advanced measuring devices are expected to capture the market from conventional measuring devices. The market for analyzers to measure automobile exhaust was 10.41 billion yen in 2009.
NTT Laboratories have created a portable gas detection device using our Hazardous Gas Detection Technology. We are currently field-testing the equipment's effectiveness for purposes such as monitoring automobile exhaust. We have been successful in detecting dilute levels (ppb:10-9 level) of benzene, toluene and xylene gases by measuring emitted gases with the portable hazardous gas detection device.
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| Figure 2 Images of emitted gas monitoring |
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2.2 Sick House Monitoring |
These days, there are fewer news reports of sick house syndrome. However, the problem of sick house syndrome caused by VOCs inside a building still exists. Monitor sensors of VOCs such as formaldehyde and toluene are needed for (1) commercial use in factories and hospitals, where precise measurements are required, and (2) home use, where portability is required. The market in Japan for advanced compact sensors is calculated to grow to 84 billion yen by 2015.
Under the Revised Building Standard Law enacted in July 2003, new homes must be equipped with a ventilation fan with 0.5 revolutions per hour (24 hours). The implementation of sick house monitoring by using VOC sensors and ventilation systems is strongly desired for super-insulated homes, which proliferate these days (see Figure 3).
Using the portable hazardous gas detection technology developed by NTT, residents can detect rarified toluene and xylene gas in a building.
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| Figure 3 Sick house monitoring |
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2.3 Monitoring Discharged Water |
Standards for water discharged from factories and work sites and water that seeps into the ground are mandated by the Water Pollution Control Law. The law requires measuring how polluted discharged water is. The market for analysis equipment to measure water pollution was 4.03 billion yen in terms of production output in 2009.
Benzene, toluene and xylene, which are VOCs, are components of gasoline. They leak from gas stations and contaminate soil and groundwater. These substances are highly toxic to the human body. They are substances that require monitoring based on environmental standards.
The Hazardous Gas Detection Technology developed by NTT Laboratories can detect benzene dissolved in liquids, making monitoring of benzene in flowing water possible.
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3. Specific Technical Explanation |
3.1 Overview of NTT's Technology |
A detection device using the Hazardous Gas Detection Technology developed by NTT (see Figure 4) is composed of a gas concentration unit and a photodetector. The gas concentration unit's adsorbent material is made of nano porous zeolite to increase adsorption efficiency. Furthermore, the photodetector inspects gas. Thus harmful VOCs existing in minute amounts in living environments can be detected.
We have also developed a sensor for detecting benzene in liquid by combining (1) technology for vapor separation of benzene from solution and (2) technology for drying/concentrating evaporated benzene. The benzene sensor for use in liquid can not only detect benzene at low concentrations (ppb), it can also monitor flowing liquid (inline monitoring).
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3.2 Advantages of NTT's Technology |
| ・ Can detect at a highly sensitive level (ppb level)
・ Can be installed in many locations because the technology is compact and portable
・ Can automatically measure hazardous gases
・ Can monitor flowing liquid
・ Easy to maintain
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| Figure 4 Basic components of the Hazardous Gas Detection Technology |
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3.3 Explanation of NTT's Technology |
In a chassis measuring 33.5cm wide, 15.5cm deep and 18cm tall, the gas detection device using NTT's Hazardous Gas Detection Technology contains a small pump for gathering gases, a UV light source, a spectrometer and two glass chips (1cm×3cm) with micro channels through which gases pass. Built into the first chip are gas adsorbent material and a thin membrane heater. Heating the adsorbent material which has captured the atmosphere after a certain period of time produces highly concentrated gas for measuring. The concentrated gas is sent to the second chip, where it undergoes UV spectroscopy. The concentration of VOCs in the environment is low and detecting them with compact equipment is extremely difficult. However, by measuring them after they have been concentrated, benzene, toluene and xylene gases can be detected at low concentrations (ppb level).
To respond to the need for measuring water pollution, we have also developed a benzene sensor for use in solutions by improving the Hazardous Gas Detection Technology. The convention method is to add carrier gas (for example, atmospheric air) to a liquid sample inside a closed container and separate aromatic hydrocarbons with the bubbling extraction process. However, this method requires a relatively large amount of liquid sample (some 100ml to 1L). And because the container must be closed, this method cannot be applied to monitoring flowing liquids. The benzene sensor for aqueous solution developed by NTT combines (1) technology for extracting benzene molecules from a solution (vapor separation with silicon tube membrane; see Figure 5) and (2) technology for concentrating gases at high humidity (drying tube for removing moisture and zeolite to concentrates gas). So it is possible to carry out monitoring of flowing liquid (inline monitoring).
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| Figure 5 Extraction of benzene molecules (evaporation separation technology) |
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3.4 Glossary |
Volatile organic compound (VOC)：
Term for organic chemical substances that are readily volatile in the atmosphere at normal temperatures and pressures. They are highly toxic, and are one type of causative agents of suspended particulate matter and photochemical oxidants.
Suspended particulate matter (SPM)：
A contaminant of the atmosphere. Particles with diameter less than 2.5μm are called fine particulate matter (PM2.5). They can easily enter deep into the lungs and cause major health problems.
Ultraviolet (UV) spectroscopy：
A method to analyze a substance by exposing it to ultraviolet light and displaying the magnitude of the substance's absorption of the UV light as an absorption spectrum of UV frequencies. Qualitative analysis can be performed on the shape of the absorption spectrum and quantitative analysis can be performed on the magnitude of the absorption. Because VOCs such as benzene, toluene and xylene have fixed absorption peaks in the 240-280nm region, they can be distinguished and identified.
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3.5 References |
(1)
Authors/Editors: Serge Camou, Akira Shimizu, Tsutomu Horiuchi, Tsuneyuki Haga
Book/Journal Title: Solid State Circuits Technologies
Publisher: Intech Book chapter
Article Title: Ppt-level Detection of Aqueous Benzene with a Portable Sensor Based on Bubbling Extraction and UV Spectroscopy
Volume Number/Page Number: pp.462-483
Year Published: 2010
(2)
Authors/Editors: S. Camou, A. Shimizu, T. Horiuchi, T. Haga
Book/Journal Title: Sensors and Actuators B
Publisher: IEICE; Elsevier B.V.
Article Title: Ppb-Level detection of benzene diluted in water with portable device based on bubbling extraction and UV spectroscopy
Volume Number/Page Number: Vol.132, No.2, pp.601-607
Year Published: 2009
(3)
Authors/Editors: S. Camou, T. Horiuchi, T. Haga
Book/Journal Title: Sensors, 2006. 5th IEEE Conference
Publisher: IEEE
Article Title: Ppb Level Benzene Gas Detection by Portable BTX Sensor Based on Integrated Hollow Fiber Detection Cell
Volume Number/Page Number: pp.235-238
Year Published: 22-25 Oct. 2006
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