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NatureInterface > No.08 > P041-046 [Japanese]

Nature Interface Frontier: Environmental Information Automatic Acquisition Device and Environmental Information Integration N-dimensional Map -- Ken Sasaki

Environmental Information Automatic Acquisition Device and Integrated N-dimensional Map for Environmental Information


Associate Professor of Graduate School of Frontier Sciences, The University of Tokyo

Issues on Environmental-Information Monitoring

Environmental issues are diverse in their complexity and scale, ranging from global scale issues such as global warming to regional issues such as acid rain and pollution of air, water and soil, and further down to volatile organic compounds (VOC) in small confined spaces that cause sick house syndrome on new house residents. In order to solve these issues, accurate and comprehensive monitoring of the environment is essential.

A sampling and analysis system for SPM (suspended particulate matter) is currently being developed at the Environmental Information Laboratory, Division of Environmental Studies, Graduate School of Frontier Sciences of The University of Tokyo. This system utilizes portable automatic sampling devices and a database that integrates diverse environmental information, which is called °»N-dimensional map for integrated environmental information°….

As an example of existing system for wide range environmental monitoring, a system called °»soramame-kun°…, which is run by Japan°«s Ministry of Environment, provides nationwide distribution data of air pollutants on the web 24 hours a day. The system measures levels of sulfur dioxide, nitrogen monoxide, nitrogen dioxide, carbon monoxide, photochemical oxidant, nonmethane hydrocarbons, SPM, and wind direction and velocity. These data are collected from 2119 measurement stations distributed across the country: 1703 general environmental atmospheric measurement station, and 416 exhaust gas monitoring station, as of year 2000. Suspended Particulate Matter (SPM) is a term given for particles smaller than several micrometers in diameter that float in the atmosphere. Particles less than 2 micrometers, which are called fine-particle, are of much concern because they may cause health problems. Smaller particles stay aloft longer in the air, and when inhaled, they reach deep into the lung and accumulate there. Furthermore, unlike gaseous matter, particulate matters are difficult to remove, and long-term deposit will eventually have impacts on respiratory organs.

Observation-systems based on fixed-point observation like the one described above is effective for wide-area coverage of environmental information, however, the number of the observation stations is not enough to obtain local environmental information of individuals in their daily life. SPM sources such as motor vehicles and factories are distributed unevenly, and movement and diffusion of SPM depend on terrain and wind velocity/direction. To increase accuracy and resolution, we need to increase the number of observation points. Setting more fixed-point stations, however, is costly and impractical. Use of portable devices is cheaper and more efficient for interpolating the data obtained from fixed-point stations.

Collecting and Analyzing Particles Floating in the Air Using Portable Device

Environmental Information Laboratory has been developing a PDA-based Automatic Environmental Information Acquisition Device, and SPM analysis system that utilizes Laser-induced Breakdown Spectroscopy (abbreviated as LBS hereafter) for componential analysis, as shown in Fig. 1 and 2. The portable device is used for collecting SPM samples as well as measuring meteorological information at the time of sampling. The samples are then brought back to the lab for analysis. Presently, these functions are evaluated by connecting commercial GPS module and meteorological sensors to a notebook computer and carrying them in a backpack as shown in Fig. 3. Figure 4 is an image of this portable device.

The system's functions and features are as follows.

1. A built-in micro-pump in the portable device sucks the air, and micro particles accumulate on a filter.

2. At the time of SPM sampling, location and meteorological data (temperature, humidity, atmospheric pressure, wind direction and velocity, etc.) are measured by the built-in GPS and other sensors.

3. Location and meteorological data are written on a RF-ID tag embedded in the paper filter.

4. The paper filters are brought back to the lab and components of the SPM are analyzed by LBS. Sampled location and meteorological data are read out from the RFID.

5. The results are added to the database, and publicized on the Internet.

Along with the componential analysis, meteorological data such as temperature, humidity, and wind direction/velocity are necessary for estimating SPM°«s source location, distribution, and diffusion patterns. Although the Meteorological Bureau°«s database is the most common meteorological information source, the distribution of the observation stations is too sparse for using the data for such analysis. This is why the meteorological sensors are built-in the portable device for SPM sampling.

Measuring location by GPS may seem unnecessary because people are carrying the device. Names of buildings, rivers, or street addresses may be easier for people to indicate location, however, numerical data from GPS, i.e. the latitude and longitude, are more compatible with GIS (geographical information system) analysis on computers. Measurement accuracy of GPS, which is in the order of 20-30 meters, is sufficient for this purpose.

RFID (Radio Frequency Identification) is a technical term for small sized IC memory chips that are capable of non-contact reading and writing. Most RFID operate without batteries because they extract electrical power from the incoming electromagnetic wave transmitted from the reader device. RFID is already used in commuter pass, and ID card, and the application field is expected to broaden in the near future.

The componential analysis used in this system is called °»Laser-induced Breakdown Spectroscopy°…. The major advantage of this method is that it does not require pretreatment of the sample such as condensation or dissolving the sample in solvent, which are common in conventional methods.

The principle of Laser-induced Breakdown Spectroscopy is shown in fig 5. A very short focused laser beam (pulse laser) irradiates a specimen placed inside a chamber. The beam breaks the specimen into elements and changes it to plasma state. Ratios of components and particle sizes are obtained from spectrum and intensity change of the light which is emitted during the transition from plasma to ground state. The current system, which is shown in Fig. 6, is being developed by associate professor Shinya Nagasaki at the Division of Environmental Studies, Graduate School of Frontier Sciences, the University of Tokyo. The pulse frequency used in the experimental system is 20Hz. A stepping motor synchronized with this repetition pulse rotates the paper filter in order to irradiate the specimen evenly. Total analysis time for one specimen is several minutes.

Figure 7 shows an example of componential analysis on SPM specimen, which was collected at a nearby traffic intersection by using a commercial micro-pump for 5 hours. This system is still under development and requires several hours of pumping to accumulate enough amounts for analysis. With proper selection of filter size and type, enhancement of pump performance, and parameter optimization of LBS, the analysis time is expected to decrease to several minutes, if the SPM concentration is near the environmental limit.

The system can be used for water quality inspection or soil analysis by changing the sampling device or sensors. Position and the meteorological data can be used as common data.

Development of portable environmental information acquisition device as described above simplifies the measurement process and increase quantity and quality of the data as well. It also enables environment-conscious non-professional people to participate in the measurement activities, and contributes to their education on environmental issues.

How To Construct An Environmental Information Database

It is a common practice to use GIS (Geographical Information System) for environmental information analysis and utilization. Currently, our laboratory is developing an °»Integrated N-dimensional Map for Environmental Information°… which integrates environmental information on GIS. Prof. Itao at the Institute of Environmental Studies, The University of Tokyo, who has proposed this system, explains that the system will form an N-dimensional space by adding multiple axes of environmental data to three-dimensional space and time. It is difficult to give a graphical representation of actual N-dimensional map, however, as shown in fig. 8, it can be imagined as stack of layers; each layer containing certain environmental data with respect to the location and time of the measurement.

The upper right part of Fig. 8 shows an example of data display of conditions for SPM sampling by the portable environmental information acquisition device. The lower right and left parts of Fig. 8 are examples of image based environmental monitoring devices currently being developed in the lab. Lower left is a solar powered autonomous alpine flora observation system that monitors plants in high mountains where climate is too harsh for long-term observation by humans. The system in the lower right part of Fig. 8 captures images and sends them to a server only when the system detects the sound from the object. These systems have meteorological sensors; the same design concept with the portable environmental information acquisition device.

Figure 9 describes construction process of the N-dimensional Map. The far left column represents environmental information acquired by sensor devices, while the far right column represents user applications for utilizing N-dimensional Map. The second column from the right is the existing GIS system. Parts surrounded by the red dashed line that require further development such as sensor interface, N-dimensional Map's database, and the user interface.

Data acquisition by portable devices and data analysis by N-dimensional map database will provide richer environmental information and better framework for effective use of the information.

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