48 Gas Detection
An additional complication is the wide range of humidity and temperatures encountered in the field. Water vapour is a major volcanic gas, and vent temperatures can reach more than 1000ºC, but due to rapid near-vent plume dispersion, temperatures and humidities at the deployment sites: typically at the crater-rim, several m to 100’s m from the vent - were dominated by local environmental conditions. Nevertheless, measurements at Mt. Erebus volcano, Antarctica, in particular, required calibrated corrections for the unusually low temperatures encountered (< -30ºC), and the instrument was field- tested to an extreme.
The data analysis shows that each volcanic plume exhibits its own chemical signature. The chemical composition of emitted gases depends on the source magma and the subsurface processes of crystallisation and re-melting, influenced by the plate-tectonic setting and the local geology. In-plume chemistry also plays a role; high-temperature near-vent chemistry is believed to generate radicals that can initiate rapid formation of sulphate aerosol. Low-temperature gas and aerosol chemistry
in the downwind plume sustains rapid autocatalytic chemical cycles as the plume disperses into the background atmosphere. Indeed, recent research3
has demonstrated that volcanic plume chemistry destroys ozone, creating mini ozone holes as it disperses downwind. Thus, measurements that characterise volcanic gas composition not only contribute towards volcano monitoring as a hazard prediction tool, but can also be used to assess local and global impacts of volcanoes, such as downwind acid deposition and impacts on the atmosphere.
Instruments used for volcanic gas observations include remote sensing methods such as Differential Optical Absorption Spectroscopy, using scattered UV-sunlight as a source(DOAS) and Fourier Transform Infra-red (FTIR) spectroscopy, sometimes using lava as an IR source!, as well as in situ gas and aerosol sampling via traditional bottle and filter- trap methods, followed by laboratory analysis. The application of electrochemical sensors to volcanology, capable of measuring gas concentrations in situ and in real time, is a relatively new development but it offers real advantages in terms of cost and sustained operation.
analysis methods. The next step is to build a network of such instruments designed for autonomous use, for deployment on an active volcano, to transmit data streams to a remote observatory (for instance via satellite comm-unications). This would enable vol- canologists to monitor in situ plume gas concentrations at different locations, in real-time. The wealth of data generated would expand our knowledge of how volcanoes work and what impacts they have on the atmosphere and environment. This approach will surely become the standard for volcano geochemical surveillance and is sure to inform hazard assessment and risk management in the future.
References
1 From the Istituto Nazionale di Geosifica e Vulcanologia:
www.ct.ingv.it
2
http://www.alphasense.com
3 Modelling Reactive Halogen Formation and Ozone Depletion in Volcanic Plumes. T.J. Roberts et al., Chemical Geology, 2009
Tjarda Roberts obtained her PhD at the University of Cambridge in 2009 in the measurement and modelling volcanic plume chemistry. Working at the interface between Atmospheric Sciences, Geography and Geology, she has developed new instruments and numerical model methods to characterise volcanic emissions and explore the impacts of volcanic plumes on atmospheric chemistry. She is now a Research Associate at the Norwegian Polar Institute where she combines her volcano-interests with research into pollution in the Arctic.
Rod Jones is a Professor of Atmospheric Science at the University of Cambridge, Department of Chemistry with over 25 years of research experience in atmospheric observations, numerical modelling and developments of novel measurement and sensor technique.
John Saffell has been Technical Director of Alphasense Ltd since it was founded in 1997. He has been involved in gas sensing and water quality monitoring for 30 years. He is chairman of the Council of Gas Detection and Environmental Measurement (CoGDEM) and works with the Technology Strategy Board, advising on UK sensor strategies.
Adam Durant is a Research Associate at the Centre for Atmospheric Science, University of Cambridge and adjunct Assistant Professor at Michigan Technological University (Department of Geological and Mining Engineering and Sciences). His research interests include deployment of Controlled METeorological balloons for gas sensing of volcanic plumes and development of carbon dioxide sensors for atmospheric measurements.
In developing our low-cost, low-power, high-durability instrument based on electrochemical sensors, we highlight the strong potential for electrochemical sensors to contribute to long-term volcano monitoring. The field-deployments demonstrated the capability of electrochemical sensors to endure the harsh, acidic environment of a volcano and to detect a range of gases in the plume-mixture, through newly developed
Acknowledgements
Clive Oppenheimer, Darryl Dawson, Christine Braban, Tony Cox, Paul Griffiths, Ray Freshwater, Oliver Durant
Norwegian Polar Institute (NPI), Natural Environment Research Council (NERC), CamBridgeSens
AUTHOR DETAILS
Dr T.J. Roberts, Norwegian Polar Institute, email:
Tjarda@npolar.no Tjarda@cantab.net
Prof. R.L. Jones,
University of Cambridge Dr J. Saffell, Alphasense Dr A.J. Durant,
University of Cambridge
New CO2 Analyser is Fast, Easy to Use and Very Accurate
Reliance on accurate indoor air quality (IAQ) monitoring is greater than ever for environmental site surveys on homes, offices and factories especially near potentially polluting sources like landfills. Border control and port inspectors may use carbon dioxide analysers with probes to discover stowaways and illegal immigrants in lorries and containers. Food packers with modified air packaging (MAP) and growers with controlled environments in e.g., glasshouses or for mushroom farming all seek accurate, reliable gas analysis.
Geotech’s (UK) new G150 carbon dioxide (CO2) analyser has the accuracy essential for IAQ measurements in very low CO2 concentrations of 0-10,000ppm. This level of accuracy is vitally important when checking, for example, sick building syndrome. Newly designed and engineered, the G150 has options for oxygen (O2), temperature, humidity and PC/Internet hook up. Checking IAQ CO2 levels is simple. Users just switch on the G150 and view the crystal-clear screen.
With backlight on its easy-to-read screen, the Geotech G150 is a replacement the earlier Geotech CD98 analyser. Geotech has developed the G150 from 30-years of experience and customer-focused research.
At the heart of the new G150, designed and built by Geotech in the UK is a custom, Geotech-designed, CO2 analysis cell. Geotech’s new infrared absorption cell has increased length for low-
levels CO2 to give maximum sensitivity and accuracy. The G150 is specifically designed for 0-10,000ppm, (0.0-1.0 %). This accuracy is essential as IAQ tests measure very small concentrations of CO2. In normal fresh air CO2 ranges between 380-420ppm (0.038-0.042%) while concerns with sick building syndrome (SBS) start with CO2 as low as 500ppm (0.05%).
Options include oxygen (O2) analysis using a factory-fitted electrochemical cell with a service replacement life of three years in air. An optional probe measures humidity and temperature. The probe, with a carry-case assists, environmental site surveyors as they move between locations. The G150-11N measures CO2, O2 humidity and temperature.
The on-board electronics and microcontroller in the G150 use the latest proven available technology which has increased data storage, ease-of-use, longer life and PC/Internet connectivity. The on-board rechargeable battery lasts for more than 12 hours. Moisture removal is built in which aids reading stability and accuracy.
Also new with the G150 is the option of a unique ID for each location against which the G150 stores a set of readings of date, time, CO2, O2, temperature and humidity. In total the G150 stores 1000 data sets. These can be screen-viewed or, via PC-USB cable, downloaded to Geotech’s optional Analyser Data Manager Software. With this, users can also download calibration events and an analyser’s set-up profiles to copy to another G150 readied for immediate use. PC connectivity also provides Internet access for remote, down-the-line diagnostics and firmware updates.
Reader Reply Card no 128
IET
May/June 2010
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68
