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The lifetime of all gas sensors is up to 3 years. As part of our cooperation, the University of Applied Sciences Nordwestschweiz ([Fachhochschule Nordwestschweiz](http://www.fhnw.ch/personen/martin-fierz)) provides ultrafine particle sensors and the necessary expertise. Furthermore, we monitor temperature and humidity in the enclosure.
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# OpenSense Deployments
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Between 2012 and 2017 we maintained two installations of measurement stations in Zurich: 10 stations on top of 10 trams in the city of Zurich and one station at the national air pollution monitoring network [NABEL](http://www.bafu.admin.ch/luft/00612/00625/index.html?lang=en) station in Dübendorf. Both deployments are briefly described below.
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Between 2012 and 2017 we maintained two installations of measurement stations in Zurich: 10 stations on top of 10 trams in the city of Zurich and one station at the national air pollution monitoring network [NABEL](https://www.empa.ch/web/s503/nabel) station in Dübendorf. Both deployments are briefly described below.
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### Tram deployment
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*Installation of an OpenSense measurement station on top of a VBZ cobra tram.*
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### Stationary deployment
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The second station is statically positioned next to the [NABEL](http://www.empa.ch/plugin/template/empa/699/*/---/l=2) station in Dübendorf and used as a long-term deployment in cooperation with [EMPA](http://www.empa.ch/)/[BAFU](http://www.bafu.admin.ch/) who kindly helped us with the installation and provide us with reference data. This deployment is running successfully since April 2011. We use the reference data obtained by this station to calibrate our sensors and to evaluate their performance under a wide range of weather conditions, which is difficult to achieve in a laboratory environment.
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The second station is statically positioned next to the [NABEL](https://www.empa.ch/web/s503/nabel) station in Dübendorf and used as a long-term deployment in cooperation with [EMPA](http://www.empa.ch/)/[BAFU](http://www.bafu.admin.ch/) who kindly helped us with the installation and provide us with reference data. This deployment is running successfully since April 2011. We use the reference data obtained by this station to calibrate our sensors and to evaluate their performance under a wide range of weather conditions, which is difficult to achieve in a laboratory environment.
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![](img/misc/db_box.jpg)
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![](img/misc/db_station_outside.jpg)
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*The NABEL station in Dübendorf used as reference.*
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For calibrating the sensors, we implemented three calibration schemes for mobile sensor nodes. We investigate single-hop and multi-hop calibration given a reference station which can be reached by the mobile stations from time to time. The first scheme implements a standard way of calibrating gas sensors while the other two approaches show different trade-offs between measurement accuracy and calibration delay. We showed though experiments that when using these calibration schemes for ozone sensors we are able to measure ozone concentrations with an average error of 2ppb compared to the measurements done by the [NABEL](http://www.empa.ch/plugin/template/empa/699/*/---/l=2) station. This is remarkable as the accuracy given in the datasheet of the sensor is 20ppb. Furthermore, we found a linear dependency of the calibration accuracy on the number of calibration hops. The accuracy loss is tolerable as long as the number of calibration hops is rather limited which is the case in public transport networks.
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For calibrating the sensors, we implemented three calibration schemes for mobile sensor nodes. We investigate single-hop and multi-hop calibration given a reference station which can be reached by the mobile stations from time to time. The first scheme implements a standard way of calibrating gas sensors while the other two approaches show different trade-offs between measurement accuracy and calibration delay. We showed though experiments that when using these calibration schemes for ozone sensors we are able to measure ozone concentrations with an average error of 2ppb compared to the measurements done by the [NABEL](https://www.empa.ch/web/s503/nabel) station. This is remarkable as the accuracy given in the datasheet of the sensor is 20ppb. Furthermore, we found a linear dependency of the calibration accuracy on the number of calibration hops. The accuracy loss is tolerable as long as the number of calibration hops is rather limited which is the case in public transport networks.
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### Participatory and personal sensing
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![](img/misc/hardware_arch_htc.png)
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