Spatio-temporal Description of Air Quality with Mobile
and Static Arrays of MOS Sensors
Serge Guillas (Statistical Science), Russell Binions & Daren Caruana (Chemistry)
Liora Malki-Epshtein (CEGE), Venus Shum (Computer Science)
About this Group
Bracelet Hardware Platform
Implementation and Data Analysis
Bracelet is the flexible, portable, modular hardware platform developed by the Computer Science
department for pervasive sensing applications. Different modules, including procesors, radio
modules, GPS modules, sensors, interface boards, external memory modules can be mixed and
matched, tailored for the application. Bracelet v1 (Figure 4) uses SPI communication bus between
the modules. Bracelet v2 (Figure 5) uses I2C buses and allows for more modules to be attached to
the platform.
A variety of air pollutants have known harmful effects on human health and the
environment. The London Air Quality Network is made of 160 continuous monitoring
sites. However, in urban settings, the concentrations of these pollutants can vary
dramatically. Hence, some streets layouts with corresponding trace may lead to
unsustainable local levels of concentrations.
We have teamed up researchers from statistical science, chemistry and computer
science departments to develop new science in pollution monitoring and modeling
with pervasive sensing technologies. The areas we work on include:-
Power
board
•!State of Art Gas Sensors – we evaluate the performance and limitation of commonly
used electrochemical gas sensors for pervasive applications
Wireless
board
A small lab trial with 5 sensor nodes (2 with CO sensors) and 1 base station (sink). The
sensor nodes take readings at regular interval and send the information back to the base
station wirelessly. The base station display the information to the user. (Figure 7)
USB-serial interface
(for programming
only)
Processor
board
•!Metal Oxide Sensors (MOS) – we research into the latest advance in MOS
technology and the suitability of the sensors for portable applications
USB
•!Wireless Sensor Network (WSN) – we research into the hardware and software
aspects of the technology
GPS
Bracelet strip (mounted on fibre glass for
development purpose)
Figure 4
•!Pollution modeling – we investigate new technique for pollution modeling using finegrain, mobile sensor data provided by WSN
…
Figure 5
Calibration
Sensor Module
The gas sensors with their sensor modules must be calibrated (Figure 6) individually before
deployment. Ideally, they should be calibrated against environmental factors including temperature
and humidity.
Several commercial Carbon Monoxide (CO) electrochemical sensors (Figure 1) were
evaluated to see if they are suitable to detect the range of street-level pollution level.
The calibration looks at their sensitivity (Figure 2) towards the gas and the response
time (Figure 3). The bigger sensors tends to have better sensitivity and quicker
response time.
RCO100F: y=103.9828x + 387.8499 mV
3CO1ET1500: y=74.4762x + 327.0358 mV
COAX: y=48.4801x + 252.2829 mV
COBX: y=63.6403x + 231.9754 mV
CO-D4: y=23.5547x + 223.3620 mV
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•! Deploy 20 sensor units in a street-canyon environment in London to collect fine-grain
temporal-spatial data.
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# 7*+0-+8)$"8,
2"#
2000
1500
1000
Research in MOS sensors involves doping the
sensors with substrate (Zeolite) to improve
selectivity towards the target gas. It has the
following competitive edges over electrochemical
sensors:-
140
120
100
80
•!MOS sensors have long life time, typically >10
years.
0
-5
40
20
0
5
10
15
CO concentration (ppm)
Figure 2
TEMPLATE DESIGN © 2008
www.PosterPresentations.com
20
25
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•! Research and develop the use of MOS sensor in pervasive monitoring.
•! Use the data collected to develop new technique for pollution modeling.
•! Investigate other similar application domains for the techniques developed.
Contact information
60
500
."+-,$/"+0
Figure 6
RCO100F
3CO1ET1500
COAX
COBX
COD4
160
2500
!8;8*2$
<"&<-
We have demonstrate the use of portable gas sensor units for pervasive pollution monitoring
application. In the near future,
Metal Oxide Sensors
180
response time (second)
ADC reading (4096 = 3.3V)
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200
3500
The Environmental Fluid Mechanics group at the Department of Civil, Environmental and
Geomatic engineering (CEGE) is our collaborator on the implementation and data
collection aspects of the project.
Future Work
The performance of electrochemical
sensors are satisfactory regarding their
sensitivity and power consumption.
However, they have relatively short life
time, typically 1-2 years. The sensors
degrade over the period, which suggest
re-calibration and re-deployment. MOS
sensors can potentially be a better option
for pervasive sensing.
Figure 1
3000
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Figure 7
5
10
15
concentration (ppm)
Figure 3
20
•!MOS sensors are very small (the sensor and
heater track are 1mmx1mm), good for portable
application.
Statistical Science Department
Serge Guillas [serge@stats.ucl.ac.uk]
Computer Science Department
Venus Shum [v.shum@cs.ucl.ac.uk]
Chemistry Department
Russell Binions [uccarbi@ucl.ac.uk]
Daren Caruana [d.j.caruana@ucl.ac.uk]
Department of Civil, Environmental
and Geomatic engineering (CEGE)
Liora Malki-Epshtein [uceslma@ucl.ac.uk]
Acknowledgement
Bridging the Gaps (BTG) funds and escalator funds